Eleven-vertex carboranes

CHAPTER

7

Eleven-vertex carboranes

7.1 OVERVIEW In the first edition of this book [1] the known chemistry of 11-vertex closo-carboranes was summarized in a few paragraphs, and the development of nido-C2B9 chemistry was still in its infancy. Since then, as the extensive compound listings in Tables 7-1–7-4 attest, huge advances in carborane chemistry generally have generally been paralleled by extensive studies on 11-vertex clusters, including the discovery of many new systems such as mono-, tri-, and tetracarbon carboranes. Much of this work has benefited from the commercial availability of C2B10H12 and B10H14 starting materials, and has been driven, in large part, by the applications of 11-vertex nido-carborane chemistry in medicine, metal extraction from radioactive waste, development of new materials, and other areas discussed in Chapters 14–17.

7.2 11-VERTEX OPEN CLUSTERS 7.2.1 Nido-CB10H13
7.2.1.1 Synthesis In contrast to dicarbon icosahedral-fragment clusters such as C2B9H13 and C2 B9 H11 2
which are typically generated by boron extraction from icosahedral C2B10 carboranes (see following Section), preparative routes for 11-vertex monocarbon nido-carboranes are quite different. The original synthesis protocol entails the incorporation of carbon into decaborane(14), B10H14 or its derivatives and is accomplished in a multistep sequence, starting with treatment with CN
or alkyl isocyanides to form C-amino nido-carboranes, in the former case via a B10H13CN2
dianion [2–8]: H3 Oþ

H2 O

Me2 SO4

B10 H14 þ 2CN





! B10 H13 CN2





! H3 N2 2CB10 H12




! 7-ðMe3 NÞCB10 H12
HCN

ð1ÞH3 Oþ

B10 H14 þ RCN ! RH2 N2 2CB10 H12








! 7-ðRMe2 NÞCB10 H12
ð2ÞMe2 SO4 ;OH

R ¼ Me; Et; n-C3 H7 ; i-C4 H9

Deamination of the C-amino derivatives with sodium or sodium hydride yields the parent nido-carborane anion [5–7]: Na=NH3 or NaH

RMe2 N-CB10 H12








! 7-CB10 H
13 Alternatively, 7-CB10 H13
salts can be obtained in a single step from nido-B10 H12 2
, a highly reactive species that is easily obtained from B10H14, by reaction with dihalomethanes [9]: CH2 X2


B10 H12 2





! 7-CB10 H
13 ð25%Þ þ B10 H13

Figure 7-1 illustrates these interconversions. Carboranes. DOI: 10.1016/B978-0-12-374170-7.00011-2 © 2011 Elsevier Inc. All rights reserved.

187

188

CHAPTER 7 Eleven-vertex carboranes

Table 7-1 Nido-CB10H13
, Nido-CB10H122
, and Nido-CB10H113
Derivatives Compound Synthesis and Characterization No substituents on boron 1-CB10 H13
7-CB10 H13


7-(Me3N)CB10H12 7-(H3N)CB10H12 7-(Me3N)CB10 H10 2
7-(Me3CNH2)CB10H12 7-ðMe3 CNHÞCB10 H12
7-[PhC(O)NH]CB10H11 7-PhCB10 H12
7-[(cyclo-C6H11)H2N]CB10H12 7-(Me3CMeHN)CB10H12 7-(Me3N)CB10H12 7-(cyclo-C6H11)Me2N-CB10H12 7-RCB10 H12
(R ¼ BuMeN, cyclo-C6H11HN) 7-RCB10 H11
(R ¼ Me3N, cyclo-C6H11Me2N) 7-RCB10 H12
[R ¼ NHC(O)Me, NMe3 þ , NHMe2 þ , NH3 þ , succinylamino] 7-(succinylamido)CB10 H12
131I biodistribution in mice 7-(H3N)CB10H12 5NH)CB10H12 7-(Me2C5 5NH)CB10H12 7-((CH2)5C5 5N)]CB10H12 7-[PhCH2(PhCH5 7-(HO2CCH2NH2)CB10H12 7-(AcNH2)CB10H12 7-[(CH2)6N4]CB10H12 7-(MeNH2)CB10H12 7-(EtNH2)CB10H12 7-([CHMe2]NH2)CB10H12 7-(BuNH2)CB10H12 7-(Me3N)CB10H12 7-(Et3N)CB10H12 7-([CHMe2]Me2N)CB10H12 7-(BuMe2N)CB10H12

Information

References

S, B, IR S, H, B, IR S X (variable temperature), thermal studies X H(2d), B(2d) B, E IR, Raman S, H, B(2d), MS S, UV, IR S, H, B S, H, B(2d), E S, X, H, B S, X, H, B S, UV, IR S, H, B, C S, X, H, B, C S, H, B, C S, X, H, B, C S, H, B S, X, H, B, C S, H, B, C S, H, B, C S, H, B, MS

[268] [5] [6,8,9] [19] [20] [112] [250] [289] [21] [6] [43] [23] [290] [290] [6] [17] [16] [2] [2] [2] [2] [2] [2] [24]

S, S S S S S S S S, S, S, S, S, S, S, S,

[24] [12] [12] [12] [12] [12] [12] [12] [10] [10] [10] [10] [10] [10] [10] [10]

H, B, MS

H, H, H, H, H, H, H, H,

B, B, B, B, B, B, B, B,

IR, IR, IR, IR, IR, IR, IR, IR,

MS MS MS MS MS MS MS MS

Continued

7.2 11-Vertex open clusters

189

Table 7-1 Nido-CB10H13
, Nido-CB10H122
, and Nido-CB10H113
Derivatives—Cont’d Compound

Information

References

7-(Me3N)CB10H12 7-(Me3-nHnN)CB10H12 7-(Et3-nHnN)CB10H12 7-(Me2S)CB10H12 7-(H3N)CB10H12 7-(Me3N)CB10H12 7-(H2PrN)CB10H12 7-ðOCNÞCB10 H12
7-[RHNC(O)NH]CB10 H12
(R ¼ H, Me, CMe3, MeCHC(O) OH, MeCHC(O)OEt, C6H4C(O)OH, CB10H12, gramicidin S)

S, S, S, S S S S S, S,

H, B, C, IR H, B, C, IR

[6] [14] [14] [12] [8] [8] [8] [11] [11]

D or C-containing substituents on boron 7-(Me3CN)CB10D5H6-9-Cl 7-(Me3N)CB10H6D5-9-Cl 7-(Me3N)CB10H6D4-6,9-Cl2 7-(Me3N)CB10H6D4-6,9-Cl2 7-(MeD2N)CB10H12-nDn, (EtD2N)CB10H12-nDn 5CHCH2 7-(Me3N)CB10H11-4-Ph-CH25 7-(H3N)CB10H11-8-CH2Ph 7-(Me3N)CB10H11-8-CH2Ph 7-MeCB10H11-(m-9,10)-MeCH
7-PhCB10H11-(m-9,10)-PhCH
[7-CB10H11-(m-9,10)-CH)]22
7-PhCB10H10-(Z5-CO)
[-(CH2)n-NH(CB10H12)-]n polymers

S, S, S, S, S, S, S, S, S, S, S, S, S,

H, B, MS H, B (2d), MS, IR H, B (2d), MS, IR H, B (2d), MS, IR MS H, B H, B H, B(2d), MS X X X, H, B, IR X H, B, C, IR (diffuse reflectance)

[21] [22] [22] [22] [10] [23] [13] [13] [35] [38] [36] [40] [43]

N- or P-containing substituents on boron 7-CB10H12-NHC(O)Me
7-(NC5H4-CH2)CB10H11 (N
B) 7-CB10H12-8-NEt3 7-CB10H12-8-PPh3 7-[(Me3Si)2CH]CB10H11-9-PPh3 7-(Me3N)CB10H10-m-PPh 7-(Me3N)CB10H10-m-PMe 7-(Me3N)CB10H10-m-PEt 7-MeCB10H9-m(9,10)-CMeH-n-PPh3 (n ¼ 5, 6) 7-MeCB10H10-8-OEt-9-CMeHPPh3 7-CB10H12-8-[(Ph2P-Z5-C5H4)Fe(Z5-C5H4PPh2)]

S, S, S, S, S, S, S, S, S, S, S,

B, IR X, H, B, MS H, B X, H, B, IR, MS X, H, B, IR, MS X, H, B, IR H, B, IR H, B, IR X, H, B, P, MS X, H, B, P, MS H, B, C, P, MS, IR

[250] [291] [21] [27] [30] [41] [41] [41] [39] [39] [31]

O- or S-containing substituents on boron 7-CB10H11-9-Me-10-OH
7-CB10H12-8-OH
7-(H3N)CB10H11-8-OHC4H8O2

H, B, IR, UV H, B, IR H, B, IR

S, B(2d) S, B(2d), H, MS S S

[26] [21] [25] [6] Continued

190

CHAPTER 7 Eleven-vertex carboranes

Table 7-1 Nido-CB10H13
, Nido-CB10H122
, and Nido-CB10H113
Derivatives—Cont’d Compound

Information

References

7-(Me3N)CB10H11-8-C(O)OH 7-(Me3N)CB10H11-8-OH 7-(Me3NCB10H11-OMe 7-(Me3N)CB10H11-4-SH (7-(Me3N)CB10H11)2S2 7-[PhC(O)NH]CB10H11-SMe2 7-(Me3Si)2CH-7-CB10H11-9-SMe2 7-(Me3N)CB10H11-2, 4-C6H3S(NO2)2 5CH 7-(RNH)CB10H10-2-SMe2-11-Me3SiR0 C5 (R ¼ PhCH2, CMe3, Bu; R0 ¼ SiMe3, Bu) 7-CB10H12-8-SMe2 (2)-1-[(Me3C)HN]CB10H10-3-C6H11-5-SMe2

S, S S, S, S, S, S, S S,

[6] [6] [14] [28] [28] [6] [15] [29] [3]

IR H, B, IR H, B(2d), MS H, B(2d), MS UV, IR H, B, MS, IR H, B, MS

S, H, B, IR, MS S, X, H, B, MS, IR

[27] [4]

Cl-, Br-, or I-containing substituents on boron 7-CB10H12Cl
7-CB10 H11 Cl2
7-CB10H12Br
7-CB10 H11 Br2
7-(Me3N)CB10H11Cl 7-(Me3N)CB10H11-n-Cl (n ¼ 7, 9) 7-(Me3N)CB10H6D5-9-Cl 7-(Me3N)CB10H11-n-Cl (n ¼ 4, 9) 7-(Me3CN)CB10H6D5-9-Cl 7-(Me3N)CB10H6D4-6,9-Cl2 7-(Me2PrN)CB10H10Cl2 7-(Me3N)CB10H11Br 7-(Me2PrN)CB10H11Br 7-(Me3N)CB10H11-4-X (X ¼ I, Br) 7-(Me3N)CB10H10-4,6-X2 (X ¼ I, Br) 7-(Me3N)CB10H11-9-I 7-(Me3N)CB10H9-4-I2
7-(Me3N)CB10H8-4,6
I2 2
anti-9-(Me3CNH2)CB10H10-conjuncto-B8H10

S, S, S, S, S, S, S, S, S, S, S, S, S, S, S, S, S, S, S,

[5] [5] [5] [5] [5] [22] [22] [21] [21] [22] [5] [5] [5] [23] [23] [23] [23] [23] [292]

Detailed NMR Studies 7-CB10 H13
7-(Me3N)CB10H12 7-CB10H11-4,6
Br2
m-PhCH-PhCB10 H11
(1,2; 1,7) m-MeCH-MeCB10 H11
(1,2; 1,7)

B B B C C

[293] [293] [293] [294] [294]

Other Experimental Studies 7-(Me3N)CB10H12 7-(Me2[CHMe2]N)CB10H12

Reactivity Reactivity

[5,29,42] [5]

IR IR B, IR IR IR, MS H, B (2d), MS, IR H, B (2d), MS, IR H, B(2d), MS H, B, MS H, B (2d), MS, IR IR, MS IR IR, MS H, B (2d; X ¼ I), E (X ¼ I) H, B (2d; X ¼ I), E (X ¼ I) H, B H, B(2d) H, B(2d) X, H, B, MS

Continued

7.2 11-Vertex open clusters

191

Table 7-1 Nido-CB10H13
, Nido-CB10H122
, and Nido-CB10H113
Derivatives—Cont’d Compound

Information

References

Reactions with amines Thermal decomposition Copolymerization of CB10 H12
anion with dibromoalkanes, crosslinking with Co3þ Controlled chemical and electrochemical substitution [Cl, D, OH, CO, C(O)OH]

[11] [13] [43]

Theoretical Studies Molecular and electronic structure calculations 1-CB10H14 CB10H14 isomers CB10 H13
isomers CB10 H12 2
isomers CB10 H13
7-ðMe3 NÞCB10 H11
7-CB10 H13
7-CB10H12-8-OH
7-(H3N)CB10 H11
7-(H2N)CB10 H12
7-(H2N)CB10H11-4-Cl
7-(H3N)CB10H12 7-ðH3 NÞCB10 H13 þ 7-(H3N)CB10H11-n-Cl (n ¼ 4,9) 7-(H3N)CB10H11-n-OH (n ¼ 8,9) 7-(H3N)CB10H11-8-NH3 7-(Me3N)CB10H12 5CHCH2 7-(Me3N)CB10H11-4-Ph-CH25 7-(Me3N)CB10H11-4-X (X ¼ I, Br) 7-(Me3N)CB10H10-4,6-X2 (X ¼ I, Br) 7-(Me3N)CB10H11-9-I 7-(Me3N)CB10 H10 2
7-(Me3N)CB10H9-4-I2
7-(Me3N)CB10H8-4,6-I2 2


Optimized geometry DFT (stability) DFT (stability) DFT (stability) Vibrational modes Optimized geometry DHf, IP, charge distribution, DHf, IP, charge distribution, DHf, IP, charge distribution, DHf, IP, charge distribution, DHf, IP, charge distribution, DHf, IP, charge distribution, DHf, IP, charge distribution, DHf, IP, charge distribution, DHf, IP, charge distribution, DHf, IP, charge distribution, DHf, IP, charge distribution, DHf, charge distribution DHf, charge distribution DHf, charge distribution DHf, charge distribution DHf, charge distribution DHf, charge distribution DHf, charge distribution

[295] [244] [244] [244] [289] [2] [21] [21] [21] [21] [21] [21] [21] [21] [21] [21] [21] [23] [23] [23] [23] [23] [23] [23]

NMR calculations 7-CB10 H13
7-CB10 H12 2
7-CB10H10-m(9,10)-CHMe


GIAO (11B) GIAO (11B) GIAO (11B)

[296] [296] [296]

Reactivity calculations 7-MeCB10H12 7-CB10 H12 2
7-CB10H10-m(9,10)-CHMe


pKa pKa pKa

[296] [296] [296]




7-ðOCNÞCB10 H12 [BH2 ðNMe3 Þ2 þ ] [7-CB10 H13
] 2]n polymers [2 2(CH2)n-NH(CB10H12)2 7-CB10 H13
, 7-(Me3N)CB10H12

bond bond bond bond bond bond bond bond bond bond bond

indices indices indices indices indices indices indices indices indices indices indices

[21]

S, synthesis; X, X-ray diffraction; H, 1H NMR; B, 11B NMR; C, 13C NMR; 2d, two-dimensional (COSY) NMR; IR, infrared data; MS, mass spectroscopic data; UV, UV-visible data; E, electrochemical data; IP, ionization potential.

192

CHAPTER 7 Eleven-vertex carboranes − CN

H

H

H

B

B

H

B

B H B B B B

B

C

H+

B B

B B

B

CN2−

B

B B B

B

B

H2RN

B B

B

H3N-CB10H12

Me3N-CB10H12

H

B

H

B B

B B

−

Me2RN+

H

B

C

Me+

H

B B

B B

B

B B B

B

B B

B H2RN-CB10H12 −

B

B B

B B

B10H14

B

B

C

B

B B

H

B

B B

B

+

RNC

H

B

C

Me+

B

− H H

H H

Me3N+

B B

H

B B10H13

−

H

H3N+

Me2RN-CB10H12

H

L+

B C

B B

H

B B

B B

Na/liq. NH3 or NaH

B

B

L = NMe3, NRMe2

B

− H

L-CB10H12

B B B B

H

B

C

B

B B B

B B CB10H−13

CH2CX2

B B

H

B

B B

B

H

H

B

X = Br, I

B

B 2−

B10H12

FIGURE 7-1 Synthetic routes to CB10 H13
B ¼ BH.

Carbon-substituted 7-RCB10 H12
derivatives can be prepared similarly, e.g., by reacting B10H14 or its derivatives with alkyl isocyanides [3,4,10], or alternatively, by the conversion of 7-H3NCB10H12 to 7-LCB10H12 species (Table 7-1) [8,11–13]. Trimethylsilyl- and trimethyltin chloride interact with B10H13CN2
to yield, following hydrolysis, 7-H3NCB10H12, while B10H13CN2
, on treatment with alkyl iodides, affords 7-LCB10H12 products, where L is NMe3 or NHEt2 [14].


H2 O

B10 H13 CN2 þ Me3 MCl




! 7-ðH3 NÞCB10 H12

ðM ¼ Si; SnÞ

H2 O

B10 H13 CN2
þ Mel




! 7-ðMe3 NÞCB10 H12 C4 H8 O

As mentioned earlier, deamination of the C-amino derivatives generates an unsubstituted CB10 H13
ion.

7.2 11-Vertex open clusters

193

Other synthetic routes to nido-LCB10H12 carboranes have been discovered, in some cases serendipitously. The C2 2C 2SiMe3, which was expected to give closo-1,2dimethyl sulfide-promoted reaction of B10H14 with Me3Si2 (Me3Si)2C2B10H10, instead formed nido-7-[(Me3Si)2CH]CB10H11-9-SMe2 as the major product, along with an alkenyl decaborane derivative [15]; the proposed mechanism involves initial complexation of the alkynyl group with decaborane, followed by intramolecular hydroboration and migration of an SiMe3 group. Nido-7-PhCB10 H12
has been prepared by boron insertion into the 10-vertex PhCB9 H11
anion with LBH3 (L ¼ THF or SMe2) [16,17], and also by thermolysis of nido-6-PhCB9 H11
, but in lower yield [16]. The acid hydrolysis of closo-heterocarboranes 1,12-EðHÞCB10 H13
, where E is P or As (Chapter 12), removes the heteroatom from the cage, forming the 1-CB10 H13
isomer 7-1 in which the skeletal carbon occupies a high-coordinate vertex that is distant from the open face [268]. The geometry of this anion is clearly revealed by its simple 11B NMR spectrum, which exhibits just two resonances of equal intensity, consistent with the presence of just two boron environments on the NMR time scale if rapid tautomerism of the B2 2H2 2B protons on the open face is assumed. -

H

B

H

B B

7-1

B B

B

B

B

B

B

B = BH C = CH

C

7.2.1.2 Structure

X-ray crystallographic structure determinations have been conducted on the parent 7-CB10 H13
ion [19,20] and on several C- and B-substituted derivatives that are listed in Table 7-1. These studies, together with NMR and other spectroscopic data (Table 7-1), confirm an icosahedral-fragment geometry with the skeletal carbon and two nonadjacent B2 2H2 2B bridging units located on the 5-membered open face (Figure 1-3, third row).

7.2.1.3 Substitution at boron: General methods A broad range of synthetic approaches has been employed to alter the chemistry at the boron vertices on the parent 7-CB10 H13
and its C-substituted derivatives. These include direct reaction with halogens, phosphines, and sulfur compounds, electrophilic iodination, electrochemistry, and hydrolysis. Still other boron-substituted nido-CB10 species have been prepared via the insertion of a carbon into B10H14 derivatives and by the reduction of 1,2-R2C2B10H10 carboranes. In many cases, the direct introduction of substituents is an ill-defined and uncontrolled process, affording multiple products and/or compounds in which the location of the entering group is not well established. However, controlled substitution has been achieved in some cases, as will be seen later. The observed patterns of reactivity of the nido-7CB10 cage correlate well with the calculated charge distributions and COSY 11B NMR data [21], which show that B (4) and B(6) are electron-rich and are most prone to electrophilic attack, while the boron sites on the open ring are relatively electropositive and are the favored locations for Lewis base addition.

7.2.1.4 Halogenation

7-CB10 H13
or its neutral charge-compensated counterpart, 7-(Me3N)CB10H12, can be chlorinated electrochemically in a concentrated HCl solution to generate the 4-chloro derivative in 67% yield [21]: 7-ðMe3 NÞCB10 H12 þ 2Cl
! 7-ðMe3 NÞCB10 H11 -4-Cl þ HCl þ 2e
Friedel-Crafts nucleophilic chlorination of the same substrate, via reaction with HCl over AlCl3, affords primarily 7-(Me3N)CB10H11-9-Cl accompanied by a small amount of 7-(Me3N)CB10H10-6,9-Cl2 [21,22]; similar treatment with DCl leads to both chorination and deuteration of the BH groups, with the addition of up to 5 D atoms [22]. Treatment

194

CHAPTER 7 Eleven-vertex carboranes

of 7-CB10 H13
or (Me2RN)CB10H12 (R ¼ Me or n-C3H7) with N-chlorosuccinimide, with or without an AlX3 catalyst, gives mono- and dichloro derivatives, while bromination of 7-CB10 H13
with Br2 generates both mono- and dibrominated products [5]. In both cases, spectroscopic and other evidence suggests that halogenation occurs preferentially at the B(4,6) locations. Electrophilic iodination of 7-(Me3N)CB10H12 affords 7-(Me3N)CB10H11-4-I and 7-(Me3N)CB10H10-4,6-I2, the structures of which have been established from COSY two-dimensional 11B NMR spectra [23]. Radioiodination of 7-RCB10H12 derivatives, employing Na131I in the presence of N-chlorosuccinimide, has generated labeled carboranes [24] for biodistribution studies in mice in conjunction with BNCT (boron neutron capture therapy) applications as discussed in Chapter 16.

7.2.1.5 Introduction of other functional groups

Treatment of 7-(Me2RN)CB10H12 (R ¼ Me or n-C3H7) with NaH in THF generates 7-CB10 H13
, in good yield, together with minor side products [5], but the reaction is complex and dependent on certain reaction conditions [21]. At low temperatures, 7-ðMe3 NÞCB10 H11
is initially formed, but on reflux and workup the products obtained are closo-2-CB10 H11
and nido-7-CB10H12-8-OH
(7-2) [21,25]. −

H

O 8 7

7-2

C

B 11

3

H 9

H

B

4

B B 10

B

B

6

2B

B

B5

B = BH C = CH

B1

A different B-hydroxyl derivative, 7-CB10H11-9-Me-10-OH
, is produced during the reaction of the “reactive” isomer of nido-C2 B10 H13
(see below) with K2CO3 in aqueous THF [26]; in this case, one of the cage carbon atoms in C2 B10 H13
is converted to an exo-polyhedral methyl group. This provides an interesting contrast to the more stable C2 B10 H13
isomer in which one cage carbon adopts a bridging role, as described later in this Section. Oxidative addition of triethylamine, promoted by thallium(III), also leads to a substitution at B(8) [21]: 7-ðMe3 NÞCB10 H12 þ Tl3þ þ NEt3 ! 7-ðMe3 NÞCB10 H10 -8-NEt3 þ Tlþ þ 2Hþ : Controlled-potential electrolysis of Csþ 7-CB10 H13
in acetonitrile results in a 2-electron oxidation process that forms CB10H12-NCMe, which, in turn, is hydrolyzed to the amide 7-CB10H12-NHC(O)Me
[250]. This behavior contrasts with that of the dicarbon carboranes, such as C2B8H10 and C2B10H12, which do not undergo electrochemical oxidation, presumably because the presence of two carbon atoms in the cage framework increases the electron density and substantially raises the oxidation potential. The unexpected formation of 7-[(Me3Si)2CH]CB10H11-9-SMe2 from B10H14 and bis(trimethylsilyl)acetylene has been mentioned earlier. A different dimethylsulfide-substituted derivative is obtained on treatment of the parent 7-CB10 H13
with SMe2 in concentrated sulfuric acid [27]: þ 7-CB10 H
13 þ SMe2 þ H ! 7-CB10 H12 -8-SMe2 þ H2

This reaction is proposed [27] to involve the initial formation of a CB10H14 intermediate that loses H2 to generate an electrophilic CB10H12 fragment, which, in turn, combines with the SMe2 electron donor. Disulfide- and thiol-substituted derivatives, such as 7-(Me3N)CB10H11-4-R (R ¼ SH, S2), can be obtained via the interaction of 7-(Me3N)CB10H12 with S2Cl2 [28]. Friedel-Crafts substitution on 7-(Me3N)CB10H12 has been employed to prepare 7-(Me3N)CB10H11-2, 4-C6H3S(NO2)2 for biodistribution studies on melanoma in mice (Chapter 16) [29].

7.2 11-Vertex open clusters

195

Phosphine derivatives are accessible by a simple displacement of the sulfide groups, as seen in the reaction of 7[(Me3Si)2CH]CB10H11-9-SMe2 with triphenylphosphine to afford 7-[(Me3Si)2CH]CB10H11-9-PPh3 [30] and in the interaction of 7-CB10H12-8-SMe2 with the same reagent to generate 7-CB10H12-8-PPh3 [27], both in good yield. Similarly, 1,10 -bis(diphenylphosphino)ferrocene and 7-CB10H12-8-SMe2 combine to form 7-CB10H12-8-[(Ph2P-Z5-C5H4)Fe(Z5C5H4PPh2)] (7-3) [31].

P

7-3

H

B

B B

H

C

Fe

B B

B B

B B

Ph2P

B = BH C = CH

B

The versatile compound 7-[(Me3Si)2CH]CB10H11-9-SMe2 interacts with CpCo(CO)2 to produce closo-CpCo [(Me3Si)2CH]CB10H11-n-SMe2] metallacarborane sandwich complexes (Chapter 13) [30]. Phosphino-substituted derivatives have also been obtained in reactions with metal phosphines, as described below.

7.2.1.6 Carbon- and phosphorus-bridged nido-CB10 clusters

The two-electron reduction of icosahedral R2C2B10H10 carboranes (R ¼ H, alkyl, aryl) with alkali metals has long been known to induce cage-opening to form nido-R2 C2 B10 H10 2
dianions, an important process that is described in Chapter 11. Protonation of these dianions generates R2 C2 B10 H11
monoanions that exist in two forms, the kinetic (so-called “reactive”) isomer 7-4 and the thermodynamically stable species 7-5 [32], also known as the “unreactive” isomer because, unlike 7-4, it does not form metallacarboranes with metal reagents [33,34]. In isomer 7-5, one of the original cage carbon atoms is protonated and adopts a bridging role on a nido-CB10 framework, as established by several X-ray diffraction studies and by ab initio calculations(Table 7-1) [35–38]. R H

− H

7-4

B B

C

B

B B

−

R R

B

C

B

B B

B B

B

B

B

B B

B C

7-5

B R

B = BH

C

B B

Carbon-bridged compounds that are structural analogues of 7-5, 7-MeCB10H9-m(9,10)-CMeH-n-PPh3 (n ¼ 5, 6) have been obtained by refluxing salts of 7-5 (R ¼ Me) with PdCl2(PPh3)2 in ethanol, a reaction that also affords a nonbridged derivative, 7-MeCB10H10-8-OEt-9-CMeHPPh3 [39]. A cluster described as a pentuply-carbonyl-bridged nido-PhCB10 cage, 7-PhCB10H10-(Z5-CO)
(7-6) has been prepared by the deprotonation of the o-carborane derivative 1,2-(HO)PhC2B10H10 ˚ in 7-6 is consistent with with 1,8-bis(dimethylamino)naphthalene (“proton sponge”) [40] The C2 2O distance of 1.245 (3) A double-bond character and indicates a transfer of the negative charge from the oxygen to the cage, while the long cluster

196

CHAPTER 7 Eleven-vertex carboranes

˚ ) implies weak but significant interaction between the carbonyl and cluster carbon atoms. C2 2C bond length (2.001 (3) A In truth, 7-6 can be equally well described as a C2B10 cage or as a carbonyl-bridged CB10 system. H

O

O

−

C

C Ph

B

C

B B

B B

B B

B

Ph

−H+

C

B

B B

B = BH

B

B B

B

B

7-6

B

B B

B

Phosphorus-bridged derivatives 7-(Me3N)CB10H10-m(9,10)-PR (R ¼ Me, Et, Ph), analogous to 7-5, have been obtained by treating 7-(Me3N)CB10H12 with Et3N, followed by RPCl2, and the structure of the PPh species (7-7) has been established by X-ray crystallography [41]. In this system the phosphorus bridges two boron atoms on the open face but has an essentially nonbonding interaction with the other three facial atoms [41]. In effect, the PPh unit functions as a 2-electron donor that replaces two B2 2H2 2B bridging hydrogens.

P

7-7 Me3N

B

H

C

B B

B B

B

B = BH B

B B B

7.2.1.7 Cage expansion reactions

Boron incorporation into 7-CB10 H13
or 7-(Me3N)CB10H12 by treatment with Et3NBH3 yeilds the icosahedral carboranes closo-1-CB11 H11
and closo-1-ðMe2 NÞCB11 H11
respectively [13,42]; that this occurs via a clean boron insertion has been demonstrated by labeling experiments with Et3N10BH3 [13]. However, the reaction of nido-7-(Me3N)CB10H118-CH2Ph with Et3NBH3 generates closo-1-(Me3N)CB11H10-7-CH2Ph as the sole product, indicating that boron insertion in this case is accompanied by cage rearrangement [13].

7.2.1.8 Polymerization The amine derivative 7-(H3N)CB10H12 can be combined with a,o-dihalogenoalkanes to generate high molecular weight alternating zwitterionic copolymers having pendant carborane groups [43]: 2NHþ ðCB10 H
2ðCH2 Þn2 2gx 7-ðH3 NÞCB10 H12 þ BrðCH2 Þn Br ! f2 12 Þ2 Cross-linking of these chains via coordination of the open-faced carborane cages to Co3þ ions leads to a metallacarborane polymer that has been characterized from spectroscopic evidence as 7-8, in which a total of three bridging protons on each pair of carborane faces is presumably retained in order to maintain electroneutrality, though their fate is not specified.

7.2 11-Vertex open clusters

197

(CH2)nHN−(CH2)n B

C

B B

B

B

B

B

Co B

B

B

B

B B

B B

B B

B C

B

7-8 B = BH

B

(CH2)nHN−(CH2)n

7.2.2 Nido-C2B9H13, nido-C2B9H12
, and nido-C2B9H112
The base-promoted, controlled extraction of boron (deboronation) from icosahedral C2B10 carboranes to generate 11-vertex nido-C2B9 species [44], discovered by Wiesboeck and Hawthorne in 1964 [45], was one of the most significant findings of the early exploration of carborane chemistry, and decades later it remains central to the synthesis of many metallacarboranes and hydrophilic functionalized carboranes for medical and other applications. The importance of this reaction is that it affords direct access to a broad array of synthetically useful nido-carboranes from commercially available 1,2-C2B10H12 (o-carborane), 1,7-C2B10H12 (m-carborane), and 1,12-C2B10H12 (p-carborane) and their derivatives using standard organic and organometallic procedures and reagents. Remarkably (and fortunately for synthetic purposes), only one boron atom is normally removed in the controlled degradation of these icosahedral systems, affording in most cases nido-C2 B9 H12
or nido-C2 B9 H11 2
anions or their substituted derivatives (Tables 7-2–7-4). Protonation of these ions in some, but not all, cases generates isolable neutral species, i.e., nido-C2B9H13 isomers or derivatives thereof. Although nine isomers of nido-C2B9H13 are theoretically possible based on skeletal carbon locations, only 7,8- and 2,9-C2B9H13 have been well-characterized as parent species. However, as is evident in the tables, many C- and B-substituted derivatives of 7,8- and 7,9-C2B9H13 and their anions are known, as are a few based on the 2,7- and 2,9-C2B9H13 isomers (Table 7-4).

7.2.2.1 Controlled deboronation of C2B10 carboranes Despite the remarkable stability of the icosahedral C2B10H12 clusters toward attack by acids or oxidizing agents (see Chapters 9 and 10), the 1,2- and 1,7-isomers and their C-substituted derivatives are susceptible to attack by nucleophiles. Bases such as alkoxides [44–53], ammonia [54–56], ammonium hydroxide [57], alkylamines [55,58–60], hydrazine [61–65], piperidine [59,66–71], pyrrolidine [72–74], and iminophosphoranes [75,76] remove a BH unit to create an 11-vertex nido-C2B9 monoanion or, in some instances, nido-C2B9-base adducts (see Tables 7-2 and 7-3). Their anions, in turn, can be deprotonated to afford the corresponding dianion or, alternatively, be protonated to form a neutral nido-carborane. C2 B10 H12 þ OH
þ 3CH3 OH ! C2 B9 H
12 þ BðOCH3 Þ3 þ H2 þ H2 O Hþ

C2 B9 H13




! C2 B9 H12





! C2 B9 H11 2
þ
H

The alkoxide method has been optimized by the use of KOH in boiling methanol, which affords the pure potassium salt with 94% yield [48]. However, in some cases the alkoxide treatment is not suitable. For example, it cannot be employed 2P to generate C-phosphino-nido-C2B9 derivatives from C-phosphino o-carboranes owing to cleavage of the Ccarborane2 bond; for such compounds, piperidine in large excess has been used successfully [67]. Fluoride ion can serve as a cage-deboronating agent [77–88], although the choice of the counterion and the solvent are important. The reaction of ethanolic CsF with 1,2-C2B10H12 or its C-substituted derivatives gives KþRR0 C2 B9 H10


198

CHAPTER 7 Eleven-vertex carboranes

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa Compound

Information nido-7,8-C2B9H13, nido-7,8-C2B9H12
,

Single-cage derivatives of and nido-7,8-C2B9H11 Neutral single-cage derivatives, no substituents on boron S (modified), B, H C2B9H13 S, IR S, H, B, C Me2C2B9H11 S, IR RC2B9H12 (R ¼ Me, Ph) S, X, H, B, C, P, IR [PH(CHMe2)2]MeC2B9H12 S, X, H, B, C [(Me2CH)2IP]PhC2B9H10 S, X (R, R0 ¼ Ph), H, B, C, P, IR [PR2(O)]R0 C2B9H11 (R ¼ Et, CHMe2, Ph; R0 ¼ H, Me, Ph) S (C5H4NMe)PhC2B9H10 5CH)C2B9H11 (R ¼ CHMe2, Me) S, X(CHMe2), H, B, C, IR, MS (C6H3R2-NH5 S, X, H, B, C, IR, MS [(PhCH2)2NCH2CH2]RC2B9H10 (R ¼ H, Me) S, H, B [H3N(CH2)n]C2B9H11 (n ¼ 2,3) S, X, H, B [H3N(CH2)3]C2B9H11N2H4 S, X, H, B (H5C5NCH2)C2B9H11 S, X, H, B, C, IR (Me2HNCH2)C2B9H11 S, X, H, B, C, IR (Me2NCH2)(HMe2NCH2)C2B9H10 S, X, H, B, C, IR (Ph2P)(HMe2NCH2)C2B9H10 S, X(Al), H, B, C, IR m-Me2M-(Me2NCH2)C2B9H10 M ¼ Al, Ga S, X, H, B, C, IR m-Me2M-(Me2NCH2)(Ph2P)C2B9H10 M¼ Al, Ga S, H, B, C, P, MS. (MePh2P)C2B9H10 selective targeting of mitochondria for BNCT [cyclo-N3P3(C5H10N)4MeCH2]C2B9H12 S, X, P, MS cyclotriphosphazene S, X, H, B, IR m(7,8)-[SCH(PPh3)S]C2B9H10 S, X, H, C m(7,8)-(S-CH2CH2-O-CH2CH2-S)C2B9H11 S, IR X2C2B9H11 (X ¼ Cl, Br, I) Neutral single-cage derivatives, D or hydrocarbon substituents on boron S, B, IR C2B9H12D S, B C2B9H(13-n)Dn S, B, IR C2B9H12-3-Ph S, H, B, C Me2C2B9Me6H5 Neutral single-cage derivatives, N-containing substituents on boron S, IR, B (RR0 ¼ H, H) RR0 C2B9H9-3-NC (R, R0 ¼ H, Me; R ¼ Me, R0 ¼ PhCH2) S [HO(O)CCH2]C2B9H10-3-NH3 C2B9H12-9-L [L ¼ NEt3, PhNMe2, C5H4N-C(O)OMe, S, B, H, IR HC(O)NMe2, MeC(O)NMe2] S, IR C2B9H11-9-NC5H5-10-X (X ¼ H, Cl)

References 2


[117] [45] [47] [45] [67] [297] [67] [105] [103] [298] [129] [129] [125] [299] [300] [300] [300] [300] [301] [302] [303] [197] [304,305]

[141] [143] [141] [92]

[306] [307] [170] [308] Continued

7.2 11-Vertex open clusters

199

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound

Information

References

R2C2B9H10-9-NC5H5 (R ¼ H, Me) C2B9H11-n-NC5H5 (n ¼ 9,10) Me2C2B9H9-n-NC5H5 (n ¼ 9,10) C2B9H12-5-NC5H5 C2B9H11-9-NC5H4Me C2B9H11-3-(NC5H5-3-Br) R2C2B9H9-9-L (R ¼ H, Me; L ¼ NMe3, pyridyl) RC2B9H11-9-NC5H5 (R ¼ Me, Ph, CH2NC5H5) C2B9H10-9-Me-11-NC5H5 C2B9H12-n-NEt3 (n ¼ 9, 10) C2B9H12-L [L ¼ terpyridine, terpyridine-O(CH2)3] Me[CH2-cyclo-NH(CH2)5]C2B9H10 Me2C2B9H10-B-CH2-cyclo-NR(CH2)5 (R ¼ H, Me) BrC2B9H10-10-BH(NC5H5)2 intermediate in deboronation of closo-1,2-BrC2B10H11 by pyridine

S, B, H, IR H S, H Raman X S, B S, X(H, pyridyl), H, B S, IR, UV S, B, H, MS S, B, H, IR S, MS

[175] [176] [176] [309] [136] [143] [133] [308] [181] [173] [310] [311] [311] [93]

S, X, H, B

Neutral single-cage derivatives, P-containing substituents on boron S, X C2B9H12-9-PPh3 S, X C2B9H11-9-PPh2H S, X (PPh3), H, B, P(PPh3) m(7,8)-S(CH2)3-C2B9H10-11-R (R ¼ PPh3, PMePh2) Neutral single-cage derivatives, O-containing substituents on boron X C2B9H12-10-O(CH2)2O(CH2)2SMe2 S, H C2B9H11-10-OC4H8 S, H Me2C2B9H9-10-OC4H8 S, B, H, IR Me2C2B9H10-9-R [R ¼ H, OC4H8] S, X, H, B, C, IR (PhCH2)2C2B9H9-OC4H8 S, B, H, IR C2B9H12-9-C(O)R (R ¼ Me, Ph) S, B, IR, MS C2B9H12-n-R (R ¼ OEt2, OC4H8; n ¼ 9,10) S, H, B, C C2B9H11-10-O(CH2CH2)2O S, H, B, C, MS Na14{B12H12[O(CH2)6-nido-7,8-RC2B9H8]12} (R ¼ H, Me) (closomer) Neutral single-cage derivatives, S-containing substituents on boron S, B(2d), H C2B9H11-9-SMe2 X S, H, B S, B(2d) S, B, H, MS S, X(Br,I), H, B(2d) C2B9H10-9-SMe2-11-X (X ¼ Cl, Br, I) S, H, B(2d) C2B9H10-9-SMe2-6-Br S, X, H, B(2d) C2B9H9-9-SMe2-6,11-Br2 S, X, H, B, C C2B9H11-10-SMe2

[192] [312] [189]

[313] [176] [176] [175] [174] [188] [187,199] [187] [215]

[112] [130] [133] [181] [177] [314] [314] [314] [127] Continued

200

CHAPTER 7 Eleven-vertex carboranes

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound

Information

References

C2B9H11-10-L [L ¼ SEtPh, SEt3, S(CH2)4] C2B9H11-10-L [L ¼ SMe2, MSEt2,(CH2)4S, OR (CH2CH2)2S, OREt2,(CH2)4O, OR(CH2)2O] C2B9H12-9-CH2SR2 [SR2 ¼ SMe2, MSEt2,(CH2)4S, OR(CH2CH2)2S, (PhCH2)2S] C2B9H11-n-SMe2 (n ¼ 5, 7, 9, 10) C2B9H11-n-SMe2 (n ¼ 9, 10) C2B9H10-9-SMe2-n-Me n ¼ 1-6, 10 C2B9H10-9-SMe2-5,6-Br2 C2B9H11-9-S(O)Me2 C2B9H11-5-S(O)Me2 Me2C2B9H9-9-SMe2

S, X[S(CH2)4], H, B, C S, B, H

[127] [181]

S, B(2d), H

[181]

S, B, H, MS S, B, IR, MS S, X(n ¼ 3, 4), H, B(2d), MS S, H, B(2d), MS S, X Raman S, B, H, IR S, H, B S, H, B, C S, B(2d), H(2d) S, X X S, X(SMe2), H, B(2d) S, X, H, B, C

[49] [199] [315] [315] [316,317] [309] [175] [133] [127] [137] [137] [131] [185] [318]

Me2C2B9H9-10-L [L ¼ SEtPh, SMe2, SEt3, S(CH2)4] PhC2B9H10-n-SMe2 (n ¼ 9, 11) PhC2B9H10-11-SMe2 Ph2C2B9H9-9-SMe2 Ph2C2B9H9-10-L (L ¼ SMe2, SMeEt, SEt2) (Me2ClE)C2B9H10-9-SeMe2 E ¼ Si, Ge

Neutral single-cage derivatives, F-, Cl-, Br-, or I-containing substituents on boron S, B, IR C2B9H11-5,6-Br2 X C2B9H10-9-NC5H5-11-I Neutral single-cage derivatives, main group metal substituents on boron S, X, H, B C2B9H12-10-endo-AlEt(PEt3)2 X C2B9H12-m(9,10)-[AlMe2] S, X(H), H, B, C, IR, MS R(Me2NCH2)C2B9H10-9-AlMe2 (N!Al) R ¼ H, Me S, X(Me), H, B, C, IR, MS R[(PhCH2)2N(CH2)2]C2B9H10-9-AlMe2 (N!Al) R ¼ H, Me S, B, H, IR, MS C2B9H12-m(9,10)-AlR2 (R ¼ Me, Et) S, H, B, C, Al Me2C2B9H11-m(9,10)-AlEt2H2 S, B, H, IR, MS C2B9H12-m(9,10)-GaEt2 IR, Raman (C2B10H11)Sn(C2B9H11) Neutral Multi-Cage Derivatives (C2B9H11)2

(Me2C2B9H10)2 m(9,10)-(C5H5N)2Si(C2B9H11)2 Si[(CH2)2SiMe2CH2)3-RC2B9H10]4 (R ¼ Me, Ph) dendrimers

S, X S, S, S, S,

X, H, B(2d) B, H, IR, UV, MS, pKa B, IR, MS X B, H, C, Si, IR,S

[141] [319]

[320] [321] [194] [194] [193] [47] [193] [322]

[202] [203] [199] [227] [198] [323] Continued

7.2 11-Vertex open clusters

201

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound

Information

References

5N-RC2B10H10 (R ¼ H, Me, Ph) RC2B9H11-N5 5)2 (R ¼ H, Me, Et) (RC2B9H11-1-N5 RC2B9H11-N2Me2-1,2-RC2B10H11 (R ¼ H, Me, Ph) RC2B9H11-N2H2-1,2-RC2B10H11 (R ¼ H, Me, Ph) 2,2-bipyridyl[OC(O)(CH2)3C2B9H11]2

S, H, IR, UV, Raman S, H, IR, UV, Raman S, H, IR (var. temp) S, H, IR (var. temp) S(CsF-promoted deboronation of 2,2bipyridine[1,2-OC(O)(CH2)3-C2B10H11]2) S, H, B, C, IR

[324] [324] [325] [325] [88]

S, X

[132]

2,200 -N2C10H6[C(O)O(CH2)3-nido-7,8-RC2B9H10]2 R ¼ H, Me bipyridyl Cationic 7,8-C2B9H12þ Derivatives [(C5H5N)S]2C2 B9 H10 þ CF3 SO3


Anionic 7,8-C2B9H12
and 7,8-C2B9H112
Single-Cage Derivatives No substituents on boron S, B, H(detailed) C2 B9 H12
S(high yield), B(2d), H(2d), thermal isomerization S (from B10H14 in alkaline solution with HCHO) S, B(2d), H S (CsF-promoted deboronation of 1,2RC2B10H11), H, C, B, IR S, H, B, IR S, B, IR B C IR Raman pKa X Kþ C2 B9 H12
X(variable temp. polymorphs), C Csþ C2 B9 H12
X C10 H6 ðNMe2 Þ2 þ C2 B9 H12
MS (electrospray ionization, Fourier transform Kþ RMeC2 B9 H10
R ¼ H, n-C4H9, n-C6H13, n-C8H17, n-C10H21 ion cyclotron resonance) Neutron diffraction S, H, B (solution þ solid state) S, X, H, B, N, XPS [N-methyl-2,200 -bipyridinium]þ C2 B9 H12
S, X, H RNC5 H5 þ C2 B9 H12
R ¼ n-butyl-, n-hexyl-, n-octyl N-alkylpyridinium salts; ionic liquids S, X, H EtMeN2 C3 MeH2 þ C2 B9 H12
1,2-Me2-3Et-imidazolium salts; ionic liquids S, X, H, B(2d) HðMe2 SOÞ2 þ C2 B9 H12


[326]

[327] [112] [113] [124] [83,88] [44,158] [141] [143] [140,328,329] [45] [330] [331,332] [333] [334] [138] [335] [138] [138] [336] [337]

[337] [123] Continued

202

CHAPTER 7 Eleven-vertex carboranes

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound þ




(Me2N)3PNH2 C2 B9 H12 [(Me2N)3PNHBNP(NMe2)3]2O2þ[C2 B9 H12
]2 C5 H10 NH2 þ C2 B9 H12
 C5H10NH (Me2N)2C10 H6 þ C2 B9 H12
[(Me2N)2C10H6 ¼ proton sponge] C2 B9 H11 2
[Mþ]2 7,8-/7,9-/2,9-C2 B9 H11 2
(M ¼ Li, Na, K) Tl2 2þ PhMeC2 B9 H9 2
{CH[C6H4-p-O(CH2)2NMe2H]CEtPh}þ C2 B9 H11
Tamoxifen analogue for BNCT MnIIð1; 10-phenanÞ3 2þ [C2 B9 H12
]2 paramagnetic salt; ferromagnetic exchange; evidence for 3D aromaticity MnIIð1; 10-phenanÞ3 2þ [C2 B9 H12
]2 ferromagnetic interactions near T ¼ 20  K [Csþ5(C2B9H12)4Cl
]n
M[N2(CHMe2)2CNR2]þ 3 (C9H7)C2 B9 H10 M ¼ Zr, Hf NR2 ¼ NMe2, NEt2, N(CH2)4 (C9H7-Me2C)C2 B9 H11
M4(acac)4ðOHÞ11 þ C2 B9 H12
(M ¼ Zr, Hf) MðenÞ3 3þ C2 B9 H12
(X
)2 mH2O (M ¼ Cr, Co; X ¼ Cl, Br; m ¼ 0-3) RuClðdppeÞ2 þ C2 B9 H12
Co(NH2Me)5Br2þðC2 B9 H12 Þ2
NH3Me]2[Co(NH2Me)3BrðC2 B9 H11 Þ2
isomers [Au9M4Cl4(PMePh2)8]þ C2 B9 H12
(M ¼ Au, Ag, Cu) [Au11[Au11(PMePh2)10]3þ[C2B9H12]3
(C4H8O)5LnCl2 þ C2 B9 H12
(Ln ¼ Y, Yb) Tlþ Me2 C2 B9 H10
MeC2 B9 H11


RC2 B9 H11
(R ¼ Me, Ph) Me2 C2 B9 H10
RMeC2 B9 H10
(R ¼ H, C7 H6 þ ) MePhC2 B9 H10
PMePh3 þ Et2 C2 B9 H10
(CH2)3C2 B9 H10
(Me2CH2CH2)RC2 B9 H10
(R ¼ H, CH2CH2OMe)

Information

References

S, X S, X

[76] [76]

S(degradation of 1,2-C2B10H12 with piperidine) S, H, B, C

[70]

S, S, S, S,

[158] [119] [338] [339]

B H, B, C IR X, H, B, C, MS

[90]

S, X, IR, Raman, ESR, MAG

[340]

S, MAG (variable T)

[341]

S, X, H, B, IR S, X, H, B, C

[342] [343]

S, H, B, C, IR S, MAG, IR, H, C S, UV, IR, C

[344] [345] [346]

S, X S, UV, Raman, IR S, UV, Raman, IR S, X, H, B, MS S, X, H, B, UV, MS S, X, H, B, C, IR S, B, H S(CsF-promoted deboronation of 1,2-RC2B10H11), H, C, B, IR UV (detailed; photometric detection) S, IR S (detailed) S, H, B, IR S, H, UV, IR UV (detailed; photometric detection) X S (CsF-promoted deboronation of 1,2-(CH2)3C2B10H10), H, C, B, IR S, X, H, B, IR

[347] [348] [348] [349] [350] [351] [352] [88] [353] [45] [46] [44] [354] [353] [355] [88] [356] Continued

7.2 11-Vertex open clusters

203

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound


(HC5 5CH2)C2 B9 H11 (cyclo-CH5 5CH-CH2)C2 B9 H10
5CH)2C2 B9 H10
(CH25 5CHCH2]C2 B9 H11
[Me(CH2)3CH5 MePhC2 B9 H10


NMe4 þ PhC2 B9 H11
PhC2 B9 H11


Ph2 C2 B9 H10
HNEt3 þ /Me3NCH2Phþ Ph2 C2 B9 H10
(two salts) (PhCH2)2C2 B9 H10
Me(cyclo-HOC6H10)C2 B9 H10
[MeO(CH2)2]C2 B9 H11
K(18-crown-6)þ [HO(CH2)2]C2 B9 H11
[MeOC(O)]C2 B9 H11
[R(O)C]C2 B9 H11
(R ¼ H, MeO) Kþ (Me2NCH2)RC2 B9 H10
(R ¼ H, Me) C)PhC2 B9 H10
(PhC C)PhC2 B9 H9 2
(PhC 0 RR C2 B9 H10
[R ¼ H, Me; R0 ¼CH2CN, C(O)NH2, CH2Ph, CN] [cyclo-7,11-CH2CH2N(CH2Ph)2]RC2 B9 H9
(R ¼ H, Me) [PhCH2NH2CH2CH2)2]RC2 B9 H10
(R ¼ H, Me) (m/p-FC6H4)C2 B9 H11
(p-FC6H4)C2 B9 H11
(p-FC6H4)2C2 B9 H10
(p-BrC6H4)C2 B9 H11
(XCH2)2C2 B9 H10
(X ¼ Cl, Br) (XCH2)C2 B9 H11


Information

References

S S, B, H, IR S, B, H, IR S, H, B, IR, MS S, H, B, IR OR S X S, H, B S (from 1-C(O)NH2-2-Ph-1,2-C2B10H10 þ EtONa/EtOH) S, H, B, IR, OR UV (conjugation between Ph and cage) UV (detailed; photometric detection) C S, B, IR, C, H X S, H, B, C, IR S, H, B S, H, B, C, IR S, X, H, B, C, IR S, X, H, B, C, IR S, B, H, C, IR S, H, B S, X (R ¼ H) S, H, B X S, IR S

[55] [357] [357] [86] [44,338] [44] [55] [128] [225] [50] [44] [358] [353] [328] [359] [360] [361] [362] [363] [364] [364] [114] [95] [365] [366] [367,368] [366] [369]

S, X(Me), H, B, C, IR, MS

[298]

S, X(Me), H, B, C, IR, MS F, UV F(Taft constants) S, H, B S, B, C, H,F S, H, B, IR S (from 1,2-(XCH2)2C2B10H10 with NH3, amines) S (from1,2-(XCH2)2C2B10H10 with 1,2-(Et2NH) C2B10H11)

[298] [370] [261] [97] [80] [44] [54] [54] Continued

204

CHAPTER 7 Eleven-vertex carboranes

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound


(Me2NCH2)C2 B9 H11 (p-C6H4NH2)C2 B9 H11
Ph(C6H10-200 -NH2)C2 B9 H10
(200 -C5H4N)(RS)C2 B9 H10
R ¼ Et, CHMe2 (NC5H4CH2)C2 B9 H11
(H5C5N-CH2)2C2 B9 H10
OSO2 CF3 þ triflate [HNC4H3-CH2]C2 B9 H11
pyrrole (H2NCH2)C2 B9 H10 3
(H3N) 2C2 B9 H10
(Me2NCH2)RC2 B9 H10
(Me2NCH2)2(H)C2 B9 H10
(NC5H4CH2)C2 B9 H11
[Me2NH(CH2)3]C2B9H11 (o/m/p-O2NC6H4)C2 B9 H11
[C(O)NH2]C2 B9 H11
[C(O)NH2]CH2C2 B9 H11
(CH2OCH2Me)[cycloN3P3(O2C12H8)2]C2 B9 H10
[cyclo-N3P3(O2C12H8)2](mOCH2)2C2 B9 H10
[MeC(O)]C2 B9 H11
PhCH2 NMe3 þ (MeOCH2)C2 B9 H11
(CH2)nN-cyclo-{C(O)C6H4C(O)}]C2 B9 H11
(n ¼ 2, 3) aminoalkyl NHMe2 þ (CH2)nNHC(O)(C6H4-oCO2)C2 B9 H11
(n ¼ 2, 3) aminoalkyl (CH2-4-Me-5-thio-1,2,4-triazol)C2 B9 H11
cyclo-CH2NHC(¼S)NHCH2-C2 B9 H10
cyclo-(4-MeC6H3)(m-S)2C2 B9 H10
NMe4 þ (Ph2P)2C2 B9 H10
[(H3B)R2P]R0 C2 B9 H10
(R ¼ Et, Ph, CHMe2; R0 ¼ Me, Ph) (PR2)R0 C2 B9 H10
(R ¼ Et, CHMe2, Ph; R0 ¼ H, Me, Ph) (R2P)2C2 B9 H10
(R ¼ Et, Ph, CHMe2, OEt) PðCH2
C2 B9 H11 Þ3 3
NMe4 þ (Ph2OP)2C2 B9 H10
(O5 5PPh2)2C2B9H11 (R2P)2C2 B9 H10
(R ¼ Ph, CHMe2) Hþ (POPh2)2C2 B9 H10
(chelated proton)

Information

References

S, H, B, C, IR S, H, B S, H, B, C, IR S, X, H, B, C, IR S, IR, MS, B, H S, X, H, B S, H, E S, H, B, C, IR S, H, IR S, X, H, B, C, IR S, X, H, B S, H, B, C, IR, MS S, H, B, C, IR, MS S, H, B S[1,2-(C(O)NH2)C2B10H10 þ EtONa/EtOH] S [1-CH2C(O)NH2-2-Ph-1,2-C2B10H10 þ EtONa/EtOH] S, X, H, C, P, IR

[371] [144] [372] [373] [374] [125] [375] [376] [377] [299] [378] [379] [379] [55,97] [50] [50]

S, X, H, C, P, IR

[380]

S, X, H, B, C, IR S, X, H, B, IR S, X(n ¼ 2), H, B, C

[114] [381] [129]

S, X (n ¼ 2)

[129]

S, S, S, S, S,

[377] [377] [382] [69] [134]

H, IR H, IR X, H, B, C X, IR, H, B, P X (CHMe2, Me), H, B, C, P

[380]

S, H, B, C, P, IR (pKa)

[67]

S, H, B, P, IR S, H, B, C, P, IR, MS S, H, C, P, B, IR S, X, H, C, IR S, H, P, H, MS, luminescence; emission excitation S, X, H, B, C, P, IR

[69] [383] [384] [385] [386] [384] Continued

7.2 11-Vertex open clusters

205

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound 0




RR C2 B9 H10 [R ¼ C(O)OH, CH2C(O)OH, C(O)OMe, CH2C(O)OMe] [HOC(O)(CH2)2]C2 B9 H11
(glucosyl-CH2)C2 B9 H11
(MeC5 5CH2)(CH2-O-CH2)C2 B9 H10
Me(HOCH2)C2 B9 H10
(MeOCH2)2C2 B9 H10
5CHMe, H) (ROCH2)2C2 B9 H10
(R ¼ CH5 Me[RO(CH2)3]C2 B9 H10
[R ¼ Et, (CH2)2OMe, nC4H9] agent for extraction of Eu, Sr, Cs R[R0 (O)C-C6H4]C2B9H9-9-125I
R ¼ CH2-b-Dglucose, R0 ¼ OH, NH(CH2)2NEt2; R ¼ H, R0 ¼ N (CH2)2NEt2 radiolabeling; binding to melanoma cells [cyanocobalamin-C(O)NH(CH2)4NH-C(O)]C2 B9 H11
(vitamin B-12) Me(PhSCH2)C2 B9 H10
(HS)2C2 B9 H10
ðEtSÞ2 C9 B9 H10
ðRSÞMeC2 B9 H10
(R ¼ Me, Et, CHMe2, n-C4H9, CH2Ph) LL0 C2 B9 H10
[L ¼ H, PPh2; L0 ¼ SEt, S(CHMe2), S(n-C4H9), SCH2Ph] ðEtSÞ2 C2 B9 H10
(PhS)(HOCH2)C2 B9 H10
(PhS)[C9H13O2-C(O)OCH2]C2 B9 H10
(MeC4H2S)C2 B9 H10
(S2NC7H4)2C2 B9 H10
(1,2-RCB10H10C)-S-(nido-7,8-RC2B9H10)
(R ¼ H, Me) HNMe3 þ ðHSÞ2 C2 B9 H10
NMe4 þ [S(CHMe2)](PPh2)C2 B9 H10
Naþ m(7,8)SCH2(CH2OCH2)3CH2S-C2 B9 H10
[HNMe3 þ ]2 [anti-7,70 ,8,80 (S2)2(C2B9H10)2]2
NMe4 þ {S[(CH2)2O]3CH2S-C2B9H10}
ðMeSÞC2 B9 H11
(SC4H3)2C2 B9 H10
thiophene (RMeHCCH2S)C2 B9 H11
(R ¼ Et, 5CMe2) thioethers CH2CH2CH5 (MeC4H2S)C2 B9 H11
(p-C6H4NCS)C2 B9 H11


Information

References

S

[369]

S, S, S S, S, S, S,

H, B, C, IR, MS H, B, C, IR, MS H, B, C, IR B, IR IR B, H, C, IR

[379] [379] [55] [387] [381] [388] [389]

S, H, B, C, MS

[390]

S, B, UV, MS, biological activity

[391]

S S E S, H, B, IR

[311] [207] [392] [393]

S, H, B, IR

[68]

E S, S, S S, S,

[392] [394] [394] [395] [77] [206]

IR, H, C, B IR, H, C, B H, B, COND X(Me), H, B, C, IR, MS

S, X, H, B S, X, H, B, IR S, X, H, C, IR

[102] [68] [196]

S, X, B

[102]

S, X UV (detailed; photometric detection) S, H, C, MS S, C

[208] [353] [396] [397]

S, B, MS S, H, B

[395] [144] Continued

206

CHAPTER 7 Eleven-vertex carboranes

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound


[(CH2)3-S-thiouracil]C2 B9 H11 cyclo-[SCH(OEt)S]-7,8-C2 B9 H10
cyclo-SC(O)CH2S-7,8-C2 B9 H10
cyclo-S[(CH2)2S]4-C2 B9 H10
cyclo-(S-C6H4-S)C2 B9 H10
cyclo-(S-X-S)C2 B9 H10
(X ¼ various organic chains) [O5 5C(m
S2)]C2 B9 H10
MeðMeSÞC2 B9 H10
Me2 Ga-RC2 B9 H10
(R ¼ H, Ph) ClPhC2 B9 H10
I2 C2 B9 H10
D or hydrocarbon substituents on boron C2B9H11D
C2B9H12-nDn
(n ¼ 0, 2-8) C2B9H11D
, C2 B9 H8 D4
(RS)R0 C2B9H9D
(R, R0 ¼ Ph; Ph, Me) R2C2B9H9-3-Ph
(R ¼ H, Me) C2B9H11-3-Et
Ph2C2B9H9-3-Et
C2B9H11-9-Me
, C2B9H10-9,11-Me2
, C2B9H99,10,11-Me3
C2B9H11-n-R
(n ¼ 5, 9) (R ¼ Me, Et, C6H13,Ph, CH5 5CH2) C2B9H11-9-CH2Ph
5CHMe) C2B9H11-9-R
(R ¼ Me, Et, n-C4H9, CH25 C2B9H11-3-Ph
Tl2C2B9H10-9-Ph
Me2C2B9H9-9-CH2Ph
CH
C2B9H11-9-CH2C
C2B9H11-m-Me C2B9H10-9,11-R2
(R ¼ Me, Et, CH2Ph) Csþ C2B9H9-9,10,11-Me3
(Ph3P)2Nþ C2 B9 H2 Me8
Si- or Ge-containing substituents on boron C2B9H11-9-R
(R ¼ SiPhMe2, SiMe3) O12Si8[(CH2)3-nido-CB9H10C
Me]88
siloxanes R ¼ Me, Ph C2 B9 H11 -GePh3
(m-H)

Information

References

S, H, IR S, IR, H S, IR, H, B, C S, C, H, IR S, IR S, H, C, IR S, IR, MS, COND S, H, IR S, B, MS S NQR (127I)

[377] [303] [398] [208] [208] [197] [399] [208] [400] [55] [401]

S, B, IR Raman S, B S, B S, B, H, C S, H, IR, B S, H, IR, B S, X, H, B, IR S, B, H, IR

[141] [330] [122] [143] [402] [94] [94] [153] [158]

S, B

[169]

S S, S, S, S, S, S, S, S, X S,

[167] [157] [143] [403] [166] [161] [165] [160] [169] [126] [92]

B B IR B B, H B, UV, IR B B X, H, B, C

S, H, C,P S, H, B, C, IR, Ms

[191] [404]

S, B, IR

[190] Continued

7.2 11-Vertex open clusters

207

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound N- or P-containing substituents on boron PhC2 B9 H10 -3-NH3
Me2C2B9H8-9-NMe3-12-Br
MeC2B9H10-9-NMe3
(2 isomers) C2B9H11-10-O(CH2)4-N3
C2B9H11-10-O(CH2)2-O-(CH2)2-N3
C2B9H11-7-(200 -pyridyl)H (PhC3N3-C5H4N)PhC2 B9 H10
triazinyl (PhC5H3N-C5H4N)PhC2 B9 H10
bipyridyl C2B9H11-9-R
(R ¼ PHPh2, PPh3) C2B9H11-3-R
[R ¼ PhC(O)NH, NMe2] C2B9H11-9-PMe2Ph C2B9H10-5(6)-Br-9-L (L ¼ 4-picoline, 3-picoline, 4-benzylpyridine, pyridine, 3-bromopyridine) (single-wall carbon nanotube)[N(CH2)4RC2 B9 H10
Naþ ]n (R ¼ Me, Ph) R2C2B9H8-9-L
(R ¼ H, Me; L ¼ NMe3, pyridyl) O- or S-containing substituents on boron C2B9H11-9-CO
C2B9H11-9-R
(R ¼ SCN, SMe) C2B9H11-9-SMe
C2B9H10-9-SMe2
Ph2C2B9H9-9-SMe2
R2C2B9H9-9-SCN
(R ¼ H, Me) R2C2B9H8-9-SMe2
(R ¼ H, Me) C2B9H11-10-O(CH2)4-O-C6H4-C(O)O
C2B9H11-10-O(CH2)2-O-(CH2)2-O-C6H4-C(O)O
C2B9H11-10-O(CH2)2O(CH2)2N3
nucleoside conjugate F-, Cl-, Br-, or I-containing substituents on boron C2B9H12-nFn
(n ¼ 1-4) stereochemistry of degradation of 1,2-C2B10 derivatives Ph2C2B9H9-3-F
C2B9H10-9,11-X2
X ¼ Cl, Br, I Me2C2B9H8-9,11-X2
X ¼ Cl, Br, I C2B9H11-5-Br
C2B9H10-5,6-Br2
C2B9H10-9,11-Br2
C2B9H11X
(X ¼ Br, I) C2B9H11-9-X
K(þ) X ¼ I, SCN

Information

References

S, S, S, S, S, S, S, S, S, S, S, S,

[405] [58] [58] [187] [187] [406] [98] [98] [191] [407] [408] [150]

H, B, IR H, MS H, MS H, B, C, IR H, B, C, IR X, H, B, C, IR, MS X, H, B, C, MS X, H, B, C, MS H, C, P IR(NMe2) X, H, B, P H, B, IR, UV, XPS

S, H, B, C, IR, boron distribution in tissue

[409]

S

[133]

S, H, C, B, IR UV (detailed; photometric detection) S, B, H, circular dichroism X S, B(2d), H(2d) S, H, B(2d), IR S S, H, B, C, IR S, H, B, C, IR S(dipolar addition [chemical ligation), H, B, IR, MS, UV

[410] [353] [179] [411] [137] [180] [133] [187] [187] [412]

S, B, F

[151]

S, H, B, IR S, H, B, MS S, H, B(2d), IR UV (detailed; photometric detection) S, B NQR (79Br,81Br) S (electrochemical), B, IR S(diaphragm electrolysis)

[153] [147] [413] [353] [143] [401] [149] [414] Continued

208

CHAPTER 7 Eleven-vertex carboranes

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound


C2B9H10-9,11-X2 K(þ) X ¼ Br, I HNMe3 þ C2B9H11-9-I
RC2B9H10-3-X
(R ¼ H, Me, Ph; X ¼ Br, I) C2B9H11-9-I
C2B9H11-5/6-I
C2B9H11-n-I
(n ¼ 5,9) C2B9H10-9,11-I2
Csþ (p-C6H4NCS)C2B9H10-9-I
MeC2B9H10I
Me2C2B9H9I
MeC2B9H9-9,11-I2
PhC2B9H10I
Ph2C2B9H9-5-I
Ph2C2B9H9-9-I
C2B9H10-2,4-I2
HNM3 þ C2B9H10-9,11-I2
Ph2C2B9H8-9,11-I2
H2 C2 B9 I9 2
H2C2B9H-1,2,4,5,6,9,10,11-I8 2
Main group metal-containing substituents on boron trans-Ir(CO)(PPh3)2(MeCN)þ C2B9H11-10SnPh3
(m
H)

Information

References

S(diaphragm electrolysis) S, X S(deboronation of 1,2-C2B10H11-3-X), X (H, I), H, B, C S, B S, H, C, B, IR NQR (127I) NQR (127I) S, X, H, B S, H, B, IR S, H, B, IR S, H, B(2d), IR S, B S, X, H, B, IR S, X, H, B, IR S, X, H, B, C, MS S, X S, X, H, B, IR S, H, B, MS S, X, H, B, MS

[414] [135] [139]

S, X, H, B, P, Sn, IR

[190]

Anionic Multi-Cage Derivatives, Nonmetal substituents ðC2 B9 H11 Þ2 2
S, B, H, IR S, B, IR, UV ðC2 B9 H11 Þ2
S, B, H, IR C2B9H11-(100 ,200 -C2B10H11)
5CHCH2-(C2B9H11)2
S, H, B, IR, MS (C2B9H11)-CH2CH5 S, H, B, C, MS, U, fluorescence C6H3-1,3,5-[(p-C6H4)nCH2
CB9H10CMe]33
3Naþ n ¼ 1, 2 S, H, B, C, MS, U, fluorescence C6H3-1,3,5-[(p-C6H4)n
C6H3-3,5-(CH2-CB9H10CMe)2]33
3Naþ n ¼ 0, 1 S, B, MS [B12{Me[(CH2)6C(O)O]C2B9H10}12]14
dodecaboranecarborane closomer S, H, B, C, IR, MS (C2B9H10C-CH2OCH2)3C-C(O)OH3
pentaerythritol dendron building-block for BNCT S, H, MS, IR, UV, interaction with DNA, meso-[MeC2B9H10-7-CH2]4porphyrin
resonance light scattering 4Naþ tetrabenzoporphyrin[(C6H4)C2B9H12]44
S, H, UV, MS, toxicity, cell uptake S, H, UV, cell accumulation, 4Kþ (porphyrin)photosensitization 5,10,15,20-ðP-C6 H4 -S-C2 B9 H10 Þ4 4
photodynamic therapy (PDT)

[143] [81] [401] [401] [144] [148] [148] [413] [145] [153] [146] [152] [135] [146] [415] [415]

[199,205] [199] [205] [86] [416] [416] [417] [418] [419] [420] [421]

Continued

7.2 11-Vertex open clusters

209

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound


M[porphyrin-CH(OH)](MeC2B9H11) (M ¼ Co, Cu, 2H) Kþ[Me(CH2)15-O-CH2]2CH-O-CH2-C2B9H11)
precursor to liposomes for BNCT CoII(C2B9H11)x porphyrinates MeC2B9H10-(CH2)3-O-P(O)(OR)-O(CH2)3C2B9H10-(CH2)2C(O)NH-C6H4-Ph3 porphyrin carboranyl phosphate diester porphyrin(C6H5)(C6H4-p-NCH2-nido-C2 B9 H10
)3 4Kþ porphyrin[CH(CN)2](C6H4-p-nido-7,8C2B9H11)44
chlorin for BNCT and PDT (photodynamic therapy) [RC2B9H9(C6H4)2]2SO2 2
(R ¼ H, Me, Ph; isomers) sulfone derivatives BNCT [RC2B9H9(CH2)2C(O)NH]2C14 H6 O2 2
(R ¼ H, Me, Ph; isomers) anthraquinone derivatives m-(CH2)n-ðRC2 B9 H11 Þ2
(n ¼ 3-5) (C2B9H10)2C6H4[C(O)OMe]
O5 5C[NMe-p-C6H4-C2B9H10]22
urea m-TosN(CH2CH2)2-ðC2 B9 H11 Þ2
1,3/1,4-C6H4(C2B9H9-9-CH2)2
SðCH2
C2 B9 H11 Þ2
S2ðRC2 B9 H10 Þ2 2
(R ¼ H, Me, Ph) disulfide-bridged ðS2 C2 B9 H10 Þ2 2
(C2B9H10)2[m-7,8-S(CH2)nS-]22
(n ¼ 1, 2) [S(Me)C2B9H10]2(CH2)n
(n ¼ 2, 3) 2,6-[(C(O)OMe)C2B9H10-8-S-CH2-]2C5H3N
SðCH2
C2 B9 H10 Þ2
{7,8-m-[S(CH2CH2O)3CH2CH2-S](7,8-C2B9H11)2}2
[MeO(CH2)2C5H4]6Ti6 ðm3
OÞ8 2þ (1,2C2B10H10)(m-S2)2(nido-7,8-C2B9H10)22
C6H4[p-CH2-O-C6H3(CH2-RC2B9H10)2]24


Information

References

S, H, cytotoxicity

[422]

S, H, B, in vitro toxicity

[423]

S, EPR, reaction with O2 S, H, B, UV (fluorescence), MS BNCT

[424] [425]

S, H, UV, MS S, UV, fluorescence emission spectrum

[426] [427]

S, H, B, C, IR

[428]

S, H, B, C, IR

[428]

S, S, S, S, S, S, S, S, S, S, S, S S, S,

[210] [429] [430] [210] [166] [214] [206] [207] [101] [208] [431] [214] [432] [433]

H, B, C, IR X, H, B, C, IR

S, H, B, C, UV, fluorescence emission

Transition metal s- and m-complexes of 7,8-C2B9H12
Ti, Zr S, (PhCH2)2C2B9H9-m-M(NEt2)2(NEt2H) (M ¼ Ti, Zr) S, C2B9H12-9-(m-H)ZrMe(C5Me4Et)2 S, (HNEt2)(Et2NS2Ti-OCH2)C2B9H10 Cr, Mo, W C2 B9 H11 -3-NC-MðCOÞ5
(M ¼ Cr, Mo, W) m(7,8)-(C3H5)(CO)2Mo(SCH2CH2S)C2B9H10 (MeC6H4)CMo(CO)(PPh2C2H4PPh2)2(O)}þMe2 C2 B9 H10


H, IR, C, B, MS H, IR, C, B, MS X, H H, IR, C, B, MS B H, B, C, IR, MS X(Me), H, B, C, IR, MS X, B B, H, IR, MS H, IR H, B, C, IR, MS

[434]

and 7,8-C2B9H112
X(Ti), H, B, C, IR X X, H, B, C, IR

S, IR, C(W) S, X, H, B S, X, H, C

[174] [435] [436]

[306] [437] [438] Continued

210

CHAPTER 7 Eleven-vertex carboranes

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound


Me2 C2 B9 H9 -3-NC-MðCOÞ5 (M ¼ Mo, W) Mo(CO) ðPh2 PC2 H4 PPh2 Þ2 þ (MeC6H4)C Me2 C2 B9 H10
Me2C2B9H10-(m-H)2W(CO)2(C5Me5) Mn MnIIð1; 10-phenanÞ3 2þ (C2 B9 H12
)2 paramagnetic salt; ferromagnetic exchange; evidence for 3D aromaticity MnIIð1; 10-phenanÞ3 2þ (C2 B9 H12
)2 ferromagnetic interactions near T ¼ 20  K Fe, Ru, Os C2 B9 H11 -3-NC-FeðCOÞ5
C2B9H12-9-Fe(CO)2Cp C2B9H12-9-Fe(CO)2(MeCN)Cp C2B9H12-(C5H4)FeCp C2B9H12-9-FeCp(CO)2 Me2C2B9H10-9-Fe(CO)2Cp [(MePh2P-Z5-C5H4)Fe(Z5-C5 H4 PPh2 þ C2B9H11-9-SMe
syn-/anti-Fe[Me(C5H4)C2B9H10]
2RuClðdppeÞ2 þ C2 B9 H12
C2B9H12-5,6,10-(m-H)3RuBr(PPh3)2 m(7,8)-[(PPh3)2ClRu(m-SPh)2]C2B9H10 (2 isomers) m(7,8)-L2ClRu[S(CH2)nS]C2B9H10 (n ¼ 1-4; L ¼ PPh3, PMe2Ph, Me2SO, 0.5 phenanthroline) 2H2 2B] m(7,8)-{(PPh3)2ClRu[S(CH2)2S]}C2B9H10 [Ru2 (PPh2)MeC2B9H10-m3-RuCl(PPh3)L (L ¼ PPh3, EtOH) m(7,8)-[(MeC6H4CHMe2)RuCl(SPh)2]-C2B9H10 Ru[(PPh2)MeC2B9H9(m-H)]2 (2 isomers) R2C2B9H7-exo-5,6,10-(m-H)3RuCl (Ph2PCHMeCH2CHMe) (R ¼ H, Me) 3,1,2-CpFe(C2B9H9)-4-SMe2-8-Hg-1000 nido-700 ,800 -C2B9H8-500 ,600 ,1000 (m-H)3RuCl(PPh3)2 NMe4 þ (C2B9H10-n-S(CH2)nS)2RuCl
(n ¼ 2, 3) RuXLL0 -(PPh2)RC2B9H10 (X ¼ Cl, H; R ¼ H, Me, Ph; L ¼ PPh3; L0 ¼ PPh3, CO, tetrahydrothiophene, C2H5OH) (terpyr)Ru[(terpyr)(C2B9H10) Ru[terpyr-O(CH2)3-C2B9H10]þ 1,2C2B10H11-1-(CH3)2-O(terpyr)


Information

References

S, IR S, H, C

[306] [438]

S, X, H, B, C, IR

[439]

S, X, IR, Raman, ESR, MAG

[340]

S, MAG (variable T)

[341]

S, S, S, S, S, S, S,

IR B, H, IR, MS B, H, IR, MS H, B X, H, B, IR, Mo¨ssbauer B, H, IR, MS B, H, C,P, IR

[306] [440] [440] [441] [442] [440] [31]

S, S, S, S, S,

H, B X X, H, B, P, IR X, H, B, P, IR X(PPh3; n ¼ 1, 4), H, B, P, IR

[441] [347] [443] [444] [445]

S, S, S, S, S,

X, IR, H, B X, H, B, P, IR X, H, B, IR X, IR, B, P, H X(Me), H, B, P, IR

[446] [447] [448] [449] [450]

S, X (trans isomer), B, P

[451]

S, X(n ¼ 2), H, B, IR S, H, B, P, IR

[445] [447]

S, H, B, IR, C, MS S, H, B, C, MS

[310] [310] Continued

7.2 11-Vertex open clusters

211

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound


(PhS)RC2B9H10-m-S, H, H)-RuClðPPh3 Þ2 (R ¼ Me, Ph) Ru[(terpyr)C2B9H10]2 [RuH(PPh3)2]-7,8(Ph2P)2C2B9H10 [Ru-P, Ru-H-B(11), Ru-H-B(2)] [RuCl(PPh3)2]-7,8(Ph2P)2C2B9H10 [Ru-P, Ru-H-B(11), Ru-H-B(2)] exo, nido-Cl((C6H5)3P)2Ru-(m-H)3-7,8-nidoC2B9H8-9-Hg-(C2B10H11) Cp*MRu(C8H12)(m-S)2(C2B9H10) M ¼ Co, Rh, Ir Cp*MRu(C8H12)(m-S)2(OMe)(C2B9H9) M ¼ Co, Rh, Ir Me2C2B9H10-(m-H)3OsCl(PPh3)2 RR0 C2B9H10-5,6,10-Os(PPh3)2Cl (3 B2 2H2 2Os) [R, R0 ¼ H, Me, PhCH2, Me; RR0 ¼ 1,2(CH2)2C6H4] Co, Rh, Ir CpCo(C5H4)-C2B9H12 Co(NH2Me)5Br2þ[C2B9H12]2
NH3Me]2[Co(NH2Me)3BrðC2 B9 H11 Þ2
isomers (C2B9H12)n[Co(en)3]X2mH2O (n ¼ 1, 2; X ¼ Cl, Br; m ¼ 0-3) Cp*CoRu(C8H12)(m-S)2(C2B9H10) Cp*CoRu(C8H12)(m-S)2(OMe)(C2B9H9) m(7,8)-[(C8H12)Rh(PPh2)2]C2B9H10 m(7,8)-{(PPh3)2Rh[S(CH2)2S]}C2B9H10 C2B9H11-(n-C9H7)Rh(C9H6) (n ¼ 9, 10) [(C8H12)Rh(PPh2)]PhC2B9H10 enantiomer [Fe(C5H4)2(m-PPh2)2Rh(m-PPh2)]PhC2B9H10 enantiomers (PhS)PhC2B9H10-Rh(C8H12) Me2C2B9H7-5,10-(Ph3P)2Rh-(m-H)2-10endo-AuPPh3 R2C2B9H9-(m-H)3-5,6,10-RhCl(PPh3)2 (R ¼ H, Me) Cp*2Rh2ðm-ClÞ3 þ RR0 C2 B9 H10
R, R0 ¼ H, Me, PhCH2 (R2P)R0 C2B9H10-Rh(PPh3)2 (R ¼ Ph, Et, CHMe2; R0 ¼ H, Me, Ph) (SPh)MeC2B9H10-Rh(PPh3)2 2B2 2H] (Ph2P)MeC2B9H10-Rh(C8H12) [2 Rh2 m(7,8)-[(Me2SCH)(PPh2)]C2B9H10-Rh(C8H12)

Information

References

S, H, B,P, IR

[444]

S, H, B, C, IR, MS H, B, P

[310] [452]

H, B, P

[452]

S, X, H, B, P

[453]

S, S, S, S,

[454] [454] [455] [456]

X(Co, Rh, Ir), H, B, IR X(Co), H, B, IR X, H, P X [Me, (CH2)2C6H4], H, B(2d), P

X S, UV, Raman, IR S, UV, Raman, IR S, UV, IR, C

[457] [348] [348] [346]

S, S, S, S, S, S, S,

[454] [454] [458] [459] [460] [461] [461]

X, H, B, IR X, H, B, IR X, H, B, P, IR X, IR X, H, B(2d), IR X, H, B, C, P, IR, OP H, B, C, P, IR

S, X S, X, H, B, P

[402] [462,463]

S, X (R ¼ H), H, B, P(H) S, X(PhCH2, PhCH2), H, B, C, IR

[464] [465]

S, X (R ¼ Ph, R0 ¼ H), H, B, P (var. T), IR

[466]

S, X, H, B, P, IR S, X, H, P, B, IR S, X, H, B, P, IR

[467] [468] [469] Continued

212

CHAPTER 7 Eleven-vertex carboranes

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound

Information

References

m(7,8)-(CH2)3C2B9H10-10-[(CH2)2C(O)O(CH2)3Me]-Rh(PPh3)2 {m-S-(S-(CH2)2-S)C2B9H10}RhCl{m-(S(CH2)2-S)-C2B9H9} [Cp*M-7,8-(SCH2C(O)OMe)(S)C2B9H10]2 (M ¼ Rh, Ir) [cyclo-SCp*IrRh(C8H12)S]C2B9H9-m(Ir,B)-OMe Cp*RhRu(C8H12)(m-S)2(C2B9H10) Cp*RhRu(C8H12)(m-S)2(OMe)(C2B9H9) NMe4 þ {Cp*ClRh[m(7,8)-(SCH2CH2(OCH2CH2)3)S] C2B9H10}
NMe4 þ [m(7,8)-(SCH2CH2S)C2B9H11MClCp*]
(M ¼ Rh, Ir) RhL4 þ ðPhSÞMeC2 B9 H10
(L ¼ PPh3, PMePh2, PEt3) [(MeOCH2)C2B9H10]-n-(C9H6)Rh(C9H7)
(n ¼ 9, 10) (Ph3P)2Rh-u-SC(O)CH2S-7,8-C2 B9 H10
(PPh3)2Rh-RR0 C2B9H9 [R ¼ PPh3, R0 ¼ Me; R ¼ R0 ¼ Me; RR0 ¼ cyclo-(CH2)3]

S, X, P

[470]

S, X, B, IR

[471]

S, S, S, S, S,

[472] [473] [454] [454] [474]

6,10-(PPh3)[P(cyclohexyl)3]Rh(m-CH2C6H4CH2)C2B9H10 4,9-(PPh3)2Rh-MePhC2B9H10 (Ph3P)2Rh(S, BH)-[m-S(CH2)3]C2 B9 H10
(Ph3P)2Rh-(RS)R0 C2 B9 H10
(R ¼ Ph, Et; R0 ¼ Me, Ph) (C8H12)Rh-(PPh2)C2 B9 H11
(C8H12)Rh(RS)R0 C2B9H11 (R, R0 ¼ Ph, Et, Me) PhC2B9H10-(n-C9H6)Rh(C9H7)
(n ¼ 9, 10) LL0 Rh-7,8-ðPh2 PÞ2 C2 B9 H10
(L ¼ CO,PPh3, PMe2Ph,PMePh2,P(OEt)3, 1,2-(Ph2P)2C2B10H10, (Ph2P)2C2B9H10,(Ph2P)2C2H4, pyridine, bipyridine, COphen) (Ph3P)2Rh(m-C4H9S)(m-Ph2P)-C2 B9 H10
[L(m-PPh2)2Rh(m-PPh2)]PhC2B9H10 [L ¼ cyclo-CH-OCMe2-O-CH, binap, Fe(C5H4)2, (CH2)4] enantiomers Cp*2Cl2Rh2[cyclo-(4-MeC6H3)(m-S)2 C2 B9 H10 þ ) [cyclo-(4-MeC6H3)(mS)2C2 B9 H10
m(7,8)-[(PPh3)2Ir(m-SMe)2]C2B9H10 C2B9H10-3,9-(m-H)2IrH2[P(p-MeC6H4)3]2 Me2C2B9H10-(m-H)2AuIrH(PPh3)3 (Ph3P)2Ir[m-7,8-S(CH2)nS-(C2B9H10)]
(n ¼ 2-4) [cyclo-EIr2Cp*(C8H12)E]C2B9H9-m(Ir,B)OMe (E ¼ S, Se) [cyclo-SRh(C8H12)CoCp*S]C2B9H10

X, H, B(Rh), IR X, H, B, IR H, B, IR H, B, IR X, H, B, IR

S, X, H, B, IR

S, H, B, IR(2d) S, IR, H, B,P S, H(variable temp), P(variable temp), C [(CH2)3] X S, H(variable temp), P X X S, H, B, P S, H, B, IR, P(variable temp) S, H, B, P, IR S, B(variable temp), H(variable temp), C S, H, B, IR(2d) S, H, B, P, IR

[474] [466] [460] [398] [475] [476] [475] [476] [476] [189] [466] [468] [402] [460] [458]

S, H, B, P, IR S, H, B, C, P, IR

[469]

S, X, H, B, C, R(catalytic hydrogenation and cyclopropanation of alkenes)

[382]

S, S, S, S, S,

B, IR

[477] [478] [462] [477] [473]

S, X, H, B, IR

[479]

X, H, X, H, X, H, H, B X, H,

B IR B, P

Continued

7.2 11-Vertex open clusters

213

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound

Information

References

Cp*IrRu(C8H12)(m-S)2(C2B9H10) [cyclo-(Ph2P
MCp*
S)]C2B9H9-3-OMe M ¼ Ir, Rh

S, H, B, IR S, X(Ir), H, B, P, IR

[454] [480]

S, S, S, S, S, S,

X, H, C, IR H, IR IR IR X, H, C, IR X, H, C, IR

[108] [481] [459] [481] [385] [111]

S, S, S, S,

X, B X, B, IR X, H, B, IR, P X (R ¼ Me), H, B, P, IR

[482] [481] [398] [483]

Ni, Pd, Pt (m-X)2Ni2[(PPh2)2C2B9H10]2 (X ¼ Cl, Br) (S-CH2CH2-S)C2 B9 H10 NiCl2
[S-(CH2)2-S]C2B9H10NiðClÞ2
[S-(CH2CH2O)3]CH2CH2-S-C2B9H10)2Ni2(Cl)2 (THF)Ni[(m-O5 5PPh2)2C2B9H10]2 [cyclo-Ph2PM(Cl)(PPh3)PPh2]C2B9H10 (M ¼ Ni, Pd, Pt) 2P) (SMe)MeC2B9H10-11-PPh2Pd(PPh3)Cl (B2 m(7,8)-[S(CH2)2S]C2B9H10-Pd(PPh3)(Cl) m(7,8)-SS[CH2C(O)OEt]C2B9H10-Pd(PPh3)2 (PPh2)RC2B9H10-11-PPh2Pd(Cl)PPh3 (R ¼ Me, H, Ph) [(C6H4)PdCMeHNMe2(PPh2)]PhC2B9H10 diastereomers {closo-3,1,2-(PMe2Ph)2Pd[(C4H2RS)C2B9H9-8PMe2Ph]}þ 7,8-(C4H2)(RS)C2 B9 H11
(R ¼ H, Me) [S(CH2CH2O)3CH2CH2S-C2B9H10]2Pd Pd2(m-Cl)2-{(CHMe2)2P}2C2B9H10]2 (S-CH2CH2-S)C2B9H10)2Pd Pd[7,8-(Ph2P)2C2B9H10]2 (Ph2P)PdCl(PPh2)]C2B9H10 Pd[(Ph2P)2C2B9H10]2 (S-(CH2CH2S)4-C2B9H10)Pd(Ph3P)(Cl) Cl2Pd2{2,6-[(C(O)OMe)C2B9H10-8-SCH2-]2C5H3N}
Cl(L)Pd(m-PR2)2-7,8-C2B9H10 (L ¼ PPh3, PMePh2) Cu, Ag, Au C2B9H10-9,10-(m-H)2Cu(PPh3)2 m(7,8)-{(PPh3)[C(O)Me2]Cu(PPh2)2}C2B9H10 m(7,8)-[(SCH2CH2S)Cu(PPh3)2]C2B9H10 m(7,8)-(SCH2CH2-O-CH2CH2-OCH2CH2S)M(PPh3)C2B9H10 (M ¼ Cu, Ag) L[(Ph2P)M(PPh3)]C2B9H10 (M ¼ Cu, Au; L ¼ SEt, SCH2Ph) Cu[(m-O5 5PPh2)2C2B9H10]2 [Au9M4Cl4(PMePh2)8]þ C2 B9 H12
(M ¼ Au, Ag, Cu) (S-(CH2)2-S)C2 B9 H10 CuCl2
(Ph3P)Cu-7,8-(Ph2P)2C2B9H10

S, X, P, H, B, C, IR, OP

[461]

S, X (R ¼ H), H, P, B, MS

[395]

S, S, S, S, S, S, S, S,

[481] [110] [481] [110] [484] [484] [481] [431]

X, B, IR X, H, B, P, IR IR H, B, IR,P X, H, C, IR X, H, C, IR IR, H IR, H, B, MS

S, H, B, IR,P

[110]

S, S, S, S,

[485] [104] [486] [487]

X, B, P X X, C, IR X (M ¼ Cu), H, B, IR

S, X (M ¼ Cu, Au; L ¼ SCH2Ph), H, B, P, IR

[488]

S, S, S, S,

[385] [349] [459] [104]

X, H, C, IR X, H, B, MS IR B, H, IR

Continued

214

CHAPTER 7 Eleven-vertex carboranes

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound

Information

References

m(7,8)-[(SCH2S)Ag(PPh3)]C2B9H10 NMe4 þ Ag(m-SCH2CH2S-C2B9H10)
2 m(7,8)-[LAg(PPh2)2]C2B9H10 (L ¼ PPh3, PMePh2, phenanthroline, dppsm, dppe) m(7,8)-[(PPh3)Ag(SCH2CH2-O-CH2CH2S)]C2B9H10 {Ag[m(SCH2CH2-O-CH2CH2-OCH2CH2-O-CH2CH2S)-C2B9H10]}n polymer (C2B9H10)2-9,90 -[Ag(SbPh3)2]2 (C2B9H10)2-9,90 -[Ag(AsPh3)2]2 (bipyridine)Agþm(7,8)-SCH2CH2S]C2 B9 H10
2O2 2CH2CH22 2 Agþ [m(7,8)-SCH2CH22 O2 2CH2CH2S]C2 B9 H10
(Ph3P)Agþ Me2 C2 B9 H10
(bipyridine)Agþ Me2 C2 B9 H10
PhCH2 NMe3 þ C2B9H11-10-Au(PPh3)
(R2P)2C2B9H10-m-AuL [R ¼ Ph, CHMe2; L ¼ PPh3, PPh2Me, P(C6H4-4-Me)3] (Ph3PAuPPh2)PhC2B9H10 [(BrAu)Ph2P]2C2B9H10 m(7,8)-(Ph3P)Au(PPh2)2C2B9H10 LAu[P(CHMe2)2]2C2B9H10 (L ¼ Ph3P, Cl2) C2B9H10-9-SMe2-m(10,11)-Au(PPh3) Me2C2B9H9-9-PPh3-(m-H)-10-AuPPh3 Me2C2B9H10-(m-H)3Au3(PPh3)3 (PPh2)2(C3H6)Au2[(PPh2)2C2B9H10]2 (Ph3As)2Au4[(m-PPh2)2(C2B9H10)]2 (C6H4OMe)2Au4[(m-PPh2)2(C2B9H10)]2 (R ¼ Ph, p-C6H4Me, p-C6H4OMe) [Au11 [Au11(PMePh2)10]3þ[C2B9H12]3
[1,2-(m-Ph2P)2C2B10H10]Au[(m-Ph2P)2C2B9H10] [1,2-(m-Ph2P)2C2B10H10]Au[(m-Ph2P)2C2B9H10]0.5 CH2Cl20.5H2O (R3)2Au4[(m-PPh2)2(C2B9H10)]2 (R ¼ Ph, p-C6H4Me, p-C6H4OMe) Au4[(Ph2P)2C2B9H10]2 Ph3PAu-7,8-Me2 C2 B9 H9
7,8-[(CHMe2)2PAu(PPh3)P(CHMe2)2]C2 B9 H9
7,8-[Ph2PAu(PPh3)PPh2]C2 B9 H9
(Me2C2B9H9)AuW(CO)2Cp(m-CC6H3Me2)


S, S, S, P, S,

[489] [490] [107]

X, H, B, IR X, H, B, IR X (L ¼ PPh3, phenanthroline, dppe), H, B, IR, C, MS X, H, B, IR

[487]

S, X, H, B, IR

[489]

S, S, S, S,

[491] [491] [489] [489]

X, H, B, IR B, H, IR IR, H, B IR, H, B

S, IR, H, B S, IR, H, B S, X, H, B, IR, P S, X (CHMe2, PPh3), H, P, H, MS, luminescence; emission excitation S, X, H, P, B S, X, P S, X, H, B, P, IR, C S, X(Cl2), H, B, P, IR S, X, H, B, IR S, X, H, B, C, P S, X, H, B, C, P S, X, H, B, P, IR, C S, X, H, B, P, MS S, X(p-C6H4OMe)

[489] [489] [492] [386] [493] [494] [106] [109] [495] [496] [496] [106] [497] [498]

S, X, H, B, UV, MS S, H, B, P, MS, IR

[350] [497]

X

[499]

S, H, P, MS, luminescence; emission, excitation S, X, H, C, IR S, H, P, B, C S, variable-temp. luminescence

[498]

S, variable-temp. luminescence S, X, H, B, C, IR

[501] [502]

[500] [463] [501]

Continued

7.2 11-Vertex open clusters

215

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound

Information

References

(Me2C2B9H10)AuW(CO)2Cp(m-CC6H3Me2) (Me2C2B9H9)2Au2(CO)2MCp(m-CC6H4Me)
(M ¼ W, Mo) (Me2C2B9H10)2Au2(CO)2MCp(m-CC6H4Me) (M ¼ Mo, W)

S, H, B, C, IR S, H, B, C, IR

[502] [502]

S, X(W), H, B, C, IR

[502]

S, X, H, C, IR S, X, distribution in EMT-6 tumor-bearing mice S, X, H, B, IR X S, H, B, IR S, X, H, B, IR S, H, B, IR S, X, H, B, IR S, H, B, P, IR S, B (R ¼ H) S, H, B, IR S, H, B, IR S, H, B

[385] [333] [195] [503] [195] [504] [195] [505] [109] [506] [505] [505] [507]

S, H, B, F S, H, B S, X, H, B, P

[507] [507] [453]

S, H, B S, B, P

[508] [508]

S, X, H, B, C, IR S, X, H, B, C, IR

[351] [509]

S, X, H, B, C, MS, IR

[510]

Pyrolysis to 2,3-C2B9H11 Oxidative degradation Reaction with Lewis bases

[226] [228] [440]

Reaction with Lewis bases

[440]

Zn, Hg Zn[(m-O5 5PPh2)2C2B9H10]2 porphyrin derivatives and Zn complexes (prepared for BNCT) C2B9H11-10-Hg(PPh3) Ph2C2B9H9-10-Hg(PPh3) C2B9H11-HgMe [(MeOCH2)2C2B9H9]-10-Hg(PPh3) Hg(C2B9H10-9-NC5H5)2 m(7,8)-(SCH2S)C2B9H10-Hg(PPh3) Hg[(Ph2P)2C2B9H10]2 (7,8-RC2B9H10)2-10-Hg
(R ¼ H, Me, CHMe2) (Ph3P)Hg[7,8-(m-S(CH2)2S)C2B9H9]
(Ph3P)Hg[7,8-(Me2S)2C2B9H9]
9-(1,2-C2B10H11)-Hg-10-(7-R-7,8-C2B9H10)
(R ¼ H, Ph, CHMe2) 9-(1,2-C2B10H11)-Hg-10-(6-F-7,8-C2B9H10)
10-PhHg-7,8-RC2 B9 H10
(R ¼ H, Ph, CHMe2) exo,nido-Cl[(C6H5)3P]2Ru-(m-H)3-C2B9H89-Hg-(1,2-C2B10H11) C2B9H11-10-Hg-9-[3,1,2-CpCo(C2B9H10)] m(H)3-Ru[P(C6H5)3]2Cl-C2B9H8-10-Hg-9[3,1,2-CpCo(C2B9H10)] Lanthanon and yttrium complexes (C4H8O)5LnCl2 þ C2 B9 H12
(Ln ¼ Y, Yb) (C4H8O)5YCl2 þ (Me2NCH2CH2) (MeOCH2CH2)C2 B9 H10
[(C4H8O)3Ln-(PhCH2)2C2B9H9]2 (Ln ¼ Sm, Yb) Other Experimental Studies Reactivity and kinetics C2B9H13 PhC2B9H12 C2B9H12-9-X (X ¼ Fe(CO)2Cp, Fe(CO)2(MeCN)Cp, Fe(CO)(CNC6H11)2Cp Me2C2B9H10-9-Fe(CO)2Cp

Continued

216

CHAPTER 7 Eleven-vertex carboranes

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound C2 B9 H12




C2 B9 H12
and derivatives (I, OH, SH, CHMe2, Cl, Br, m
S) 5CH2) RC2B9H12 (R ¼ Me, Ph, CMeH5 C2B9H9-5,6,10-(m
H)3-RuCl(PPh3)2 C2B9H11I
Kþ RC2 B9 H11
(R ¼ H, Me, CHMe2) Kþ Me2 C2 B9 H10
C2B9H11.py(X)
[py (X) ¼ pyridine derivatives] (Me2NCH2)C2 B9 H11
C2 B9 H11 2


C2B9H10-3-R2
(R ¼ Et, Ph) C2B9H11-9-Me
, C2B9H10-9,11-Me2
, C2B9H99,10,11-Me3
C2B9H11-n-I
(n ¼ 5, 9), C2B9H10-9,11-I2
Me2C2B9H8-3-Ph2
Me2C2B9H9-9-CH2Ph
PhC2 B9 H11
PhC2 B9 H10 2
(optically active) R2C2B9H10-L (L ¼ Me2S, Me2SCH2, C6H5N, C6H5NCH2; R ¼ H, Me, Ph) (FC6H4)C2 B9 H10 2
Catalysis (PPh3)2Rh-(SPh)MeC2B9H10 RR0 C2B9H9-10-L (R, R0 ¼ H, Me; L ¼ SEtPh, SMe2, SEt3, S(CH2)4) (R2P)R0 C2B9H11-Rh(PPh3)2 (R ¼ Ph, Et, CHMe2; R0 ¼ H, Me, Ph) (C5Me4Et)2(CH3)Zr-C2B9H12 Cp*2MeZr-C2B9H12 [CH2-O-bicyclo-C7H4O(CHMe2)CH2RuCl2(C3H4N2mes2)]C2 B9 H11
mes ¼ mesitylene

Information

References

Electrochemical bromination, iodination Deuteration Oxidative degradation Oxidation B insertion Chromatographic separation

[149] [122,158] [183] [511] [219,223] [512]

Kinetics of formation Reaction with Br2 131 I exchange pKa pKa Bridging H tautomerism Ni complexation B insertion Methylation mechanism Me2S-BBr3 insertion ! 1,2-C2B10H11-3-Br B insertion with B2(CH2)4 Sn, Ge, Pb insertion Benzylation B insertion Deuteration

[59] [443] [154] [513] [513] [142] [371] [514] [159] [218] [220] [515] [167] [94] [158]

Pd-catalyzed cross-coupling with RMgX ! 5CH2 C2B9H11R (R ¼ Me, Et, C6H13, Ph, CH5 B insertion Protonation, rearrangement Rearrangement PhB insertion, OR Liquid chromatographic separation of enantiomers, OR F(Taft constants)

[169] [94] [161] [225] [224] [516]

Catalysis of 1-alkene hydrogenation Thermal conversion ! closo-C2B9H11

[467] [127]

Catalytic hydrogenation

[466]

Olefin polymerization catalysis Olefin polymerization catalysis Catalyst for ring-opening metathesis

[435] [435] [517]

[261]

Continued

7.2 11-Vertex open clusters

217

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound

Information

References

m-(CH2)3C2B9H11-8-[(CH2)2C(O)O(CH2)3Me]-Rh(PPh3)2 [L(m-PPh2)2Rh(u-PPh2)]PhC2B9H10 [L ¼ cycloCH2 2O2 2CMe22 2O2 2CH, binap, Fe(C5H4)2, (CH2)4] enantiomers (Ph3P)2(H)Rh2 2C2B9H11

Rh-catalyzed hydroboration; metal-promoted alkene insertion into B-H bond Enantioselective hydrogenation catalysis

[470]

[(Ph2P)2C2B9H10]2Ru (B2 2H2 2Ru) (Ph3P)2Rh(m
Ph2P)(m
H)-RC2B9H10 (R ¼ H, Me) (Z4-C8H10)Rh(m
Ph2P)(m
H)2-MeC2B9H9 (Ph3P)2ClRuþ-7,8-R2 C2 B9 H10
(Ph3P)2Rh-m-(CH2)3-7,8-C2B9H10 m-[-(Ph3P)2(H)Rh2 2CB9H10C2 2CMeCH2-]x[CMe{C(O)OMe}CH2]y- methacrylate copolymer Cp*2ClXRh2[cyclo-(4-MeC6H3)(m-S)2C2 B9 H10 ]þ[cyclo-(4-MeC6H3)(m-S)2C2 B9 H10
(X ¼ Cl,H) Other applications C2 B9 H12


C2B9H11-9-SMe
C2B9H11-5-Br
C2B9H10-thymidine
for BNCT (targeting tumor cells) RC2 B9 H10
(R ¼ Me, Ph, SMe) RR0 C2B9R00 nXm
(R,R0 ,R00 ¼ H, aryl, aryl; X ¼ H, halogen) 5CMe)C2 B9 H11
isopropenyl (CH25 5CHMe)C2 B9 H11
(CH25 (thymidine)C2 B9 H10
for BNCT (targeting tumor cells) (nido-C2B9)4porphyrins HO(O)C(CH2)2C2B9H10X
(X ¼ H,

131

I,

211

At)

Heterogenized on solid support; catalysis of hydrogenation and isomerization of 1-hexene Catalysis of Kharasch addn of CCl4 to olefins Cyclopropanation catalysis Cyclopropanation catalysis Olefin cyclopropanation catalysis Catalysis of hydrosilanolysis of alkenyl acetates Catalysis of isomerization and hydrogenation of olefins Catalytic hydrogenation and cyclopropanation of alkenes

Herbicide; fungicide; insecticide Mechanism of formation of Ni-B alloys from sulfamic acid electrolytes containing the carborane anion Electroless Ni coating Ni-B electroplates with low B content Ni-B alloy electroplates Electrophoresis; ion mobility; chiral separation) Electrophoresis; ion mobility; chiral separation) Phosphoryl transfer assay Electrophoresis; ion mobility; chiral separation) Defoliant-desiccant Synthesis of methyl methacrylate copolymers) Copolymerization with vinyl monomers Phosphoryl transfer assay Toxicity; DNA damage; light activation; sensitizer for BNCT; photodynamic therapy of tumors in vivo studies of radioiodinated and astatinated derivatives for cancer therapy

[461]

[518] [519] [520] [520] [521] [522] [523,524] [382]

[525] [526]

[527] [528] [529] [530] [530] [74] [530] [531] [532] [533] [74] [534]

[535] Continued

218

CHAPTER 7 Eleven-vertex carboranes

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound


RC2B9H10X (R ¼ (CH2)2C(O)NH(CH2)2Me, amino and amido groups; X ¼ H, 131I, 211At) DTPA {m-[m-C6H4(CH2)2]C2B9H11)(C2B9H10X)}2
X ¼ H, 131I, 211At) “Venus flytrap” complexes C2B9H10X2
biotin derivatives (X ¼ I, 125I, 211At) antibody pretargeting exo,nido-(Ph3P)2ClRu-7,8-Me2C2B9H10 Theoretical Studies Molecular and electronic structure calculations C2B9H13 isomers

C2 B9 H11 2
isomers

C2 B9 H11
C7 H6 þ C2 B9 H12
isomers

C2B9H10-9-SMe2
C10 H6 ðNMe2 Þ2 þ C2 B9 H12
[Mþ]2C2 B9 H11 2
(M ¼ Li, Na, K) cyclo-[(CH2) 2-S-(CH2) 2]O-C2 B9 H10
C2 B9 H11
C7 H6 þ tropylium C2B9H11-9-Me
(PH3)Au(Ph2P)2C2B9H10 (model) C10 H6 ðNMe2 Þ2 þ C2 B9 H12
(R3)2Au4[(m- PPh2)2(C2B9H10)]2 (R ¼ Ph, p-C6H4Me, p-C6H4OMe)

Information

References

in vivo studies of radioiodinated and astatinated derivatives for cancer therapy in vivo studies of radioiodinated and astatinated derivatives for cancer therapy

[535]

S, H, B

[536]

Controlled synthesis of poly(methyl methacrylate) with amines

[537]

MNDO, dipole moment DFT, stability Geometry Effects of exo-substitution on stability and electronic properties; interactions with biomolecules ab initio Electron density distribution MNDO, dipole moment MS-Xa electronic structure DFT, stability Effects of exo-substitution on stability and electronic properties; interactions with biomolecules ab initio: face H - double minimum geometry optimization ab initio: face H - double minimum geometry optimization DFT, stability Effects of exo-substitution on stability and electronic properties; interactions with biomolecules Electron density distribution GIAO NMR: MP2 covalence or strong ion pairing between M and anions Molecular modeling [CHARMm] ab initio charge-transfer GIAO; NMR þ geometry DFT population analysis Neutron diffraction ab initio

[538] [244] [118] [539]

[535]

[540] [411] [538] [541] [244] [539]

[121] [121] [244] [539]

[411] [138] [119] [542] [543] [118] [386] [138] [498] Continued

7.2 11-Vertex open clusters

219

Table 7-2 Selected Nido-7,8-C2B9H13, Nido-7,8-C2B9H12
, and Nido-7,8-C2B9H112
Derivativesa—Cont’d Compound

Information

References

Isomerization calculations RC2 B9 H11
isomers (R ¼ H, Ph)

Cage rearrangement

[544]

GAIO, 11B shifts GAIO, 11B shifts ab initio GIAO C, IGLO GAIO, 11B shifts GAIO, 11B shifts H NMR ab initio

[296] [296] [122] [140] [296] [296] [90]

Calculated 31P shifts; nido clusters show þI [e donor] effect, closo clusters show -I [e acceptor] effect; pKa

[67]

pKa pKa Electrophilic/nucleophilic attack pKa pKa

[296] [296] [545] [296] [296]

NMR calculations C2B9H13 C2 B9 H12


C2 B9 H11 2
C2B9H11-9/10-SMe2 PSHþ C2 B9 H12
[PS ¼ proton sponge ¼ (Me2N)2C10H6] (PR2)R0 C2 B9 H10
(R ¼ Et,CHMe2, Ph; R0 ¼ H, Me, Ph) Reactivity calculations C2B9H13 C2 B9 H12
C2 B9 H12
isomers C2 B9 H11 2
C2B9H11-9/10-SMe2

S, synthesis; X, X-ray diffraction; H, 1H NMR; B, 11B NMR; C, 13C NMR; F, 19F NMR; N, 14N NMR; P, 31P NMR; 2d, two-dimensional (COSY) NMR; IR, infrared data; MS, mass spectroscopic data; UV, UV-visible data; E, electrochemical data; ESR, electron spin resonance data; MAG, magnetic susceptibility; COND, electrical conductivity; OR, optical rotation; XPS ¼ X-ray photoelectron spectra. a A more extensive listing (TABLE 7-2 Extended) can be found online at http://www.elsevierdirect.com/companion.jsp? ISBN=9780123741707.

Table 7-3 Nido-7,9-C2B9H13, Nido-7,9-C2B9H12
, and Nido-7,9-C2B9H112
Derivatives Compound Synthesis and Characterization Neutral 7,9-C2B9H13 Single-Cage Derivatives C2B9H11-NMe3 Me2C2B9H9-10-NEt3 C2B9H12-C(O)R (R ¼ Me, Ph) (p-FC6H4)2C2B9H11 C2B9H11-10-L [L ¼ NMe3, (Me2CH)2NH, C5H5N] (H3N)C2B9H12 5CMe2, HN5 5C(CH2)6, RC2B9H12 [R ¼ HN5 HN5 5C6H3(OMe)2] iminium

Information

References

S, S, S, S, S, S, S,

[255,256] [155] [188] [80] [170] [546] [546]

H, B, B B, H, H, B, H, B, H, B, H, B,

IR IR C, F IR C, IR, UV C, IR, UV

Continued

220

CHAPTER 7 Eleven-vertex carboranes

Table 7-3 Nido-7,9-C2B9H13, Nido-7,9-C2B9H12
, and Nido-7,9-C2B9H112
Derivatives—Cont’d Compound

Information

References

C2B9H11-PMe3 (MePh2P)C2B9H10 selective targeting of mitochondria for BNCT C2B9H11-n-SMe2 (n ¼ 8, 10)

S, H, B, IR S, H, B, C, P, MS.

[255,256] [301]

S, H, B, MS

[49]

Neutral 7,9-C2B9H13 Multi-Cage Derivatives RH2C3N2(C2B9H11)2 (d,l, meso) [R ¼ H, MeOC(O)]

S, H, B, C, IR, MS

[212]

7,9-C2B9H12
and 7,9-C2B9H112
Single-Cage Derivatives No substituents on boron S(deboronation of 1,7-C2B10H12 at 100  C) C2 B9 H12
S, H, B, MS S, B, IR S, H, B, IR S, H, B S, B(T1) S, X, H, B, C PSHþ C2 B9 H12
[PS ¼ proton sponge ¼ (Me2N)2C10H6] S, IR [LnðBH4 Þ2 þ ]2 C2 B9 H12
(Ln ¼ La, Nd, Er) S, X [(Me2N)3PN]2BN(H)PðNMe2 Þ3 þ C2 B9 H12
S [hydrazine þ 1,7-(p-XC6H4)C2B10H11 N2 H5 þ (XC6H4)C2 B9 H11
(X ¼ H, Cl, Br)] S, H, B, IR S, H, B S, H, B, IR Me2 C2 B9 H10
S PhC2 B9 H11
S, H, B Ph2 C2 B9 H10
S (degradation of 1,7-[C(O)NH2]2C2B10H10) Mþ [C(O)NHPh]2C2 B9 H10
(M ¼ H, Cs) S, H, cytotoxicity M[porphyrin-CH(OH)](Me2CH-C2B9H11)
(M ¼ Co, Cu, 2H) [CH25 5C(Me)C(O)OCH2]2C2 B9 H10
S, IR D or hydrocarbon substituents on boron C2B9H11D
C2B9H12-nDn
(n ¼ 0, 2-8) C2B9H11-8-Me
C2 B9 H10 Me2
C2B9H10-8-Me2
[Mþ]2 C2 B9 H11 2
(M ¼ Li, Na, K) C2B9H11R
(R ¼ Me, Bu) C2B9H11-10-Me
C2B9H11-n-Me
(n ¼ 3, 8, 10) C2B9H10-8,10-Me2
C2B9H10-10,11-Me2


S, S, S, S, S, S, S, S, S, S S

B, IR B H, B H, B B H, B, C H, B, IR B H, B, C

[88] [49] [141] [44] [158] [155] [90] [547] [75] [65] [44] [225] [44] [52] [87] [548] [422] [388]

[141] [122] [158] [158] [159] [119] [115] [157] [118] [160] [160] Continued

7.2 11-Vertex open clusters

221

Table 7-3 Nido-7,9-C2B9H13, Nido-7,9-C2B9H12
, and Nido-7,9-C2B9H112
Derivatives—Cont’d Compound

Information

References

C2B9H9-8,10,11-Me3 C2B9H8-m,8,10,11-Me4
C2B9H11-endo-Me
CH
C2B9H11-8-CH2C C2B9H11-1,6-(C6H4-p-Me)


S, S S, S, S,

[160] [160] [118] [165] [81]

N- or P-containing substituents on boron C2B9H7Me2NH2OH
C2B9H11-10-CD3CN
C2 B9 H11 -CHðCNÞ2
C2 B9 H11 -10-CHðCNÞ2
{N2[C(O)OH](CH2C6H5)H}2C2B9H11 [HOC(O)(CH2)2]C2 B9 H11
RC2B9H10-PPh3 (R ¼ H, Ph)

S, H, B S, H, B, C S, H, B, IR S, S, B S, H, B, C, IR, MS S(aqueous F
), H, B, C, IR, MS S, X(H), H, B, P, IR

[160] [118] [115] [155] [379] [84] [549]

H, B, IR S (cleavage of 1,7-C2B10H11-9-I), H, B S, H, C, B, IR S, IR

[115] [53] [81] [79]

S, H, B, C, F, IR S, IR S S, X, H, B X, H, B S, B (see ref. 256 for better assignments) S, B S, H, B, IR

[82] [388] [52] [87] [87] [255] [155] [256]

X

[550]

F-, Cl-, Br-, or I-containing substituents on boron C2 B9 H10 Br2
Me2C2B9H9-1,6-Br2
RR0 C2B9H9-n-F
(n ¼ 3, 10; R, R0 ¼ Me, Ph, 4-FC6H4) C2B9H11-1/6-X
(X ¼ F, Cl, Br, I)

S (from 1,7-C2B10H10-9,10-Br2) S, B S, H, B, C, F, IR S, H, C, B,F, IR

[52] [155] [82] [81]

Transition Metal s- and m-complexes (C2B9H12)[M4(acac)4(OH)11]þ (M ¼ Zr, Hf) RC2B9H10-m(10,11)-OsIVHCl(PPh3)2 (R ¼ H, Ph) C2B9H11-m(10,11)-OsIVH2(PPh3)2

S, MAG, IR, H, COND S, X(H), H, B, P, IR S, X(H), H, B, P, IR

[345] [549] [549]




O- or S-containing substituents on boron C2B9H11-C5 H7 O4
C2B9H11-n-OBu
(n ¼ 1, 5) C2B9H11-1,6-OH
RR0 C2 B9 H10
(R ¼ C6H4OH, C6H4NO2; R ¼ H; R ¼ R0 ¼ C6H4OPh, C6H4NO2, NC5H4, C6H4NH2) RR0 C2 B9 H10
(R, R0 ¼ Me, Ph, 4-FC6H4) (HOCH2)2RC2 B9 H10
C2 B9 H10
(p-XC6H4)C2 B9 H11
(X ¼ Cl, Br) Ph2C2B9H9-n-OEt10
(n ¼ 2, 3) Ph2C2B9H9-10-OH
Me2C2B9H9-OR
(R ¼ Me, Et, CHMe2) Me2C2B9H9-m(3,4)-O2 C6 H4
Me2C2B9H9-3-OR (R ¼ Me, Et,CHMe2) (from 1,7-Me2C2B10H10) C2B9H11-8-SMe2

H, B H, B, C B, IR H, C, B, IR

Continued

222

CHAPTER 7 Eleven-vertex carboranes

Table 7-3 Nido-7,9-C2B9H13, Nido-7,9-C2B9H12
, and Nido-7,9-C2B9H112
Derivatives—Cont’d Compound

Information

References

S, IR S, H, B, IR S, H, B, IR

[79] [115] [115]

oxidative degradation B insertion deuteration C, IGLO B, C, H Raman Raman F3CSO3H ! cage closure to 2,3-C2B9H11 131 I exchange H2SO4 ! cage closure to 2,3-C2B9H10-X B, proton rearrangement HPLC separation degradation with Br2; B insertion OR B, proton rearrangement H2SO4!cage closure to 2,3-RR0 C2B9H9 F3CSO3H ! cage closure to 2,3(FC6H4)2C2B9H8-4-F F (Taft constants) F (Taft constants) F, UV H2SO4 ! cage closure to 2,3-C2B9H10-B-Me [mixture] MeC(O)OH ! nido-2,8-C2B9H12-11-Me

[228] [223] [122] [140] [551] [552] [552] [118] [154] [118] [161] [512] [553] [44] [161] [118] [118]

geometry DFT, stability MNDO, dipole moment MNDO, dipole moment DFT, stability MNDO, dipole moment Geometry DFT, stability covalence or strong ion pairing between M and anions

[118] [244] [538] [538] [244] [538] [540] [244] [119]




C2B9H12 Multi-Cage Derivatives 1,4-[7,9-(p-BrC6H4)C2B9H10]2C6 H4 2
C2B9H11(1,10-C2B8H9)
C2B9H11(1,10-C2B8H8Ph)
Other Experimental Studies PhC2B9H12 C2 B9 H12


C2B9H11D
C2B9H11-10-OEt C2B9H11I
C2B9H11-1(6)-X
(X ¼ Cl, I)
C2B9H11-8-Me
RC2 B9 H11
(R ¼ OH, OMe) PhC2 B9 H11
, Ph2 C2 B9 H10
d,l-PhC2 B9 H11
Me2C2B9H9-8-CH2Ph
RR0 C2 B9 H10
(R, R0 ¼ H, Me, Ph) (FC6H4)2C2B9H9-n-F
(n ¼ 3, 10) (FC6H4)C2 B9 H11
(FC6H4)2C2 B9 H10 2
(m/p-FC6H4)C2 B9 H11
C2B9H11-n-Me
(n ¼ 8, 10) C2B9H11-10(11)-endo-Me
Theoretical Studies Molecular and electronic structure calculations C2B9H13 C2B9H13 isomers C2 B9 H12
C2 B9 H12
isomers C2 B9 H11 2
C2 B9 H11 2
isomers [Mþ]2 C2 B9 H11 2
(M ¼ Li, Na, K)

[261] [261] [370] [118] [118]

Continued

7.2 11-Vertex open clusters

223

Table 7-3 Nido-7,9-C2B9H13, Nido-7,9-C2B9H12
, and Nido-7,9-C2B9H112
Derivatives—Cont’d Compound

Information

References

cage rearrangement cage rearrangement

[544] [544]

PSHþ C2 B9 H12
[PS ¼ proton sponge ¼ (Me2N)2C10H6] C2B9H11-n-Me
(n ¼ 1, 2, 3, 6, 8, 10) C2B9H11-endo-Me
C2B9H11-10,11-u-Me
C2B9H11-11-MeCN
C2B9H11-10-CD3CN
Me2C2B9H8-3,4-m-(OCH2CH2O)
Me2C2B9H8-10,11-m-(OCH2CH2O)


B, C, H, DFT spin-spin coupling GIAO (11B) IGLO H NMR ab initio GIAO; NMR þ geometry GIAO; NMR þ geometry GIAO; NMR þ geometry GIAO; NMR þ geometry GIAO; NMR þ geometry GIAO; NMR þ geometry GIAO; NMR þ geometry

[551] [296] [140] [90] [118] [118] [118] [118] [118] [118] [118]

Reactivity calculations C2 B9 H12
C2 B9 H12
isomers

pKa charge distribution, reactivity predictions

[296] [545]

Isomerization calculations C2 B9 H12
isomers PhC2 B9 H11
isomers NMR calculations C2 B9 H12


S, synthesis; X, X-ray diffraction; H, 1H NMR; B, 11B NMR; C, 13C NMR; F, 19F NMR; 2d, two-dimensional (COSY) NMR; IR, infrared data; MS, mass spectroscopic data; UV, UV-visible data; MAG, magnetic susceptibility; OR, optical rotation; COND, electrical conductivity.

Table 7-4 Nido-2,7-, 2,8-, and 2,9-C2B9 Derivatives Compound Synthesis and Characterization C2B9H13 derivatives 2,7-C2B9H12-11-Me

2,7-C2B9H10D2-11-Me 2,7-C2B9H11-6,11-Me2 2,7-Me2C2B9H10-3-CH2Ph 2,7-Me2C2B9H10-11-CH2Ph 2,9-C2B9H13

Information

References

S, B X H C IR, Raman IR, Raman S, H, B S S, X, H, B S, B, IR, UV, MS S, H, C, B ED

[118,158,161] [163] [118,158] [118] [164] [164] [158] [162] [161] [91] [90] [120] Continued

224

CHAPTER 7 Eleven-vertex carboranes

Table 7-4 Nido-2,7-, 2,8-, and 2,9-C2B9 Derivatives—Cont’d Compound

Information

References

S S S S, H, B, C S, H, B S, H, B S (degradation of 1,12-C2B10H12), B, H S, X, H, B, C S, H, B, C

[158] [158] [158] [118] [158] [158] [89] [90] [119]

Deprotonation, rearrangement Deprotonation, rearrangement

[161] [161]

Geometry Geometry Geometry Geometry Geometry Geometry Geometry Covalence or strong ion pairing between M and anions

[118] [118] [118] [118] [118] [118] [118,120] [119]

GIAO GIAO H NMR ab initio NMR: MP2

[118] [118] [90] [119]




C2 B9 H12 derivatives 2,7-C2B9H11-11-Et
2,7-C2B9H11-11-Bu
5CHCH2)
2,7-C2B9H11-11-(CH5 2,7-C2B9H11-11-Me
2,7-C2B9H10-6,11-Me2
2,9-C2 B9 H12
PSHþ2,9-C2 B9 H12
[PS ¼ proton sponge ¼ (Me2N)2C10H6] [Mþ]2 2,9-C2 B9 H11 2
(M ¼ Li, Na, K) covalence or strong ion pairing between M and anions Other Experimental Studies 2,7-C2B9H12-11-Me 2,7-Me2C2B9H10-11-CH2Ph Theoretical Studies Molecular and electronic structure calculations 2,7-C2B9H13 2,7-C2B9H12-11-Me 2,8-C2B9H13 2,8-C2B9H12-7-Me 2,8-C2B9H11-7-Me
2,9-C2B9H13 [Mþ]2 2,9-C2 B9 H11 2
(M ¼ Li, Na, K) NMR calculations 2,7-C2B9H12-11-Me (n ¼ 7, 11) 2,7-C2B9H11-n-Me
(n ¼ 7, 11) PSHþ 2,9-C2 B9 H12
[PS ¼ proton sponge ¼ (Me2N)2C10H6] [Mþ]2 2,9-C2 B9 H11 2
(M ¼ Li, Na, K)

S ¼ synthesis; X, X-ray diffraction; H, 1H NMR; B, 11B NMR; C, 13C NMR; IR, infrared data; MS, mass spectroscopic data; UV, UV-visible data.

salts in high yields (Table 7-1). Under these conditions, 1,7-C2B10H12 is unreactive, but it is degraded to nido7,9-C2 B9 H12
in 66% yield by CsF in diethylene glycol dimethyl ether at 100 C [88]. Base attack occurs regiospecifically at the most electropositive boron vertex, which in 1,2-C2B10H12 is B(3) or equivalently B(6), and in 1,7-C2B10H12 is B(2) or B(3), these being the boron atoms adjacent to two carbons (Figure 7-2). In 1,12-C2B10H12, a nonpolar system, all 10 borons carry identical charge and hence are equally electrophilic. The decreasing polarity in the series 1,2-, 1,7-, and 1,12-C2B10H12 is reflected in progressively lower reactivity toward base attack in the order 1,2 > 1,7 > 1,12. Indeed, deboronation of 1,12-C2B10H12 does not occur with alkoxide ions and

7.2 11-Vertex open clusters

H 10

8

B

7

B 12

B

C 2

B

11

9

B4 C

B

−[B+]

B5

B

C

5

1,2-C2B10H12

12

B

9

2

B 11 B

B

B4 C

6

B

2−

B

11

B

B

3

B

5

B 4B

2

B

B C

6

8

7

B

B2

3

B B1 2−

7,9-C2B9H11 2−

B C

7

B

−

B 2

−H+

9C

7,9-C2B9H−12

8

B

6

8

11

B

B C

B1

B3

12

10

11

B

9C

1,7-C2B10H12

2

2−

H

B 10

7

B

3

B

7,8-C2B9H11

B 4B

B5

7

B

7,8-C2B9H−12

5

1

6

8

B1

10

−[B+]

C

5

B 4B

2

B C

9B

B1

−

B

B

3

B3 8

−H+

7

B B

B = BH C = CH

B 10

6

8

11

B

B C

9B

B 4B

10

11

B

1

6

7C

2−

−

B3

225

9

B

B C

10

4

−[B+]

9C 5

1

6

B B 10

1,12-C2B10H12

B5

H

B

B 4B

B

6

8

B 3

B B1

2,9-C2B9H−12

10

11

−H+

9C 5

7

C

11

B

B B

B 2

4B

B

6

8

B 3

B

B B 7

C

2

B1 2− 2,9-C2B9H11

FIGURE 7-2 Conversion of icosahedral C2B10H12 carboranes to nido-C2 B9 H12
and nido-C2 B9 H11 2
(dicarbollide) anions via deboronation and deprotonation. The location of the bridging hydrogen atom in 7,8-C2 B9 H12
can vary (see discussion).

requires stronger conditions such as KOH in propanediol at elevated temperature or KOH in the presence of crown ethers [89–91], affording the 2,9-C2 B9 H12
ion (Figure 7-2). Similar degradation of the B-octamethyl-o-carborane 1,2-H2C2B10H2Me8 in KOEt/DME yields the nido7,8-H2 C2 B9 H2 Me8
ion, which can be protonated to H2C2B9H3Me8 [92]. The mechanism of extraction of boron from C2B10H12 cages is only partially understood and is difficult to study in detail, as in most cases the reaction proceeds rapidly toward completion with the formation of nido-C2B9 and monoboron products. However, an attack by the iminophosphorane N(H)P(NMe2)3 on 1,2-C2B10H12 initially forms adduct 7-9 in which the icosahedral cluster has been opened but the base-complexed boron remains attached to the cage, although connected by just three atoms. Further reaction with the base removes this boron entirely and releases the nido-7,8-C2 B9 H12
anion [75]. While not proved in the general case, adducts such as 7-9 are probable intermediates

226

CHAPTER 7 Eleven-vertex carboranes

in some base-promoted deboronations of icosahedral carboranes. A structurally different intermediate, 7-10, has been isolated during the deboronation of 1,2-BrC2B10H11 by pyridine [93], and its more open geometry reflects the presence of two electron-donor pyridines on the base-complexed boron atom. The crystallographically established cage architecture of 7-9 resembles the structure of the nido-C2 B10 H10 2
cluster that is generated by the reduction of 1,2-C2B10H12, as described in Chapter 11, and is formally derived from a 13-vertex closo polyhedron by the removal of a 6-coordinate vertex. L

H

NC5H5

B

C5H5N B

C C

B B

7-9

B

B

B

B

B B

B

H

Br

B B = BH C = CH L = N(H)P(NMe2)3

C C

B B

7-10

B

B

B

B

B B

The same iminophosphorane reagent also deboronates 1,7-C2B10H12, but the reaction is sluggish compared to that of 2H---N hydrogen-bond interthe 1,2 isomer, initially yielding a 1,7-C2B10H12 N(H)P(NMe2)3 adduct that features a C2 action; on heating at 50  C, this adduct is slowly converted to a salt of nido-7,9-C2 B9 H12
[75]. Para-carborane (1,12C2B10H12) is unreactive toward N(H)P(NMe2)3 even in refluxing toluene. In general, base-induced deboronation of C-substituted and C,C0 -disubstituted derivatives of the C2B10H12 isomers leads to the formation of the corresponding nido-C2B9 anions, but in B-substituted carboranes, the results can be different, depending on the location of the attached groups. In some cases, base attack is completely blocked, as in 3,6-dialkyl derivatives of 1,2-C2B10H12 which are unreactive toward nucleophiles [94]. Not surprisingly, the presence of strongly electron-attracting or electron-releasing groups on the cage can markedly affect the reaction rate toward bases, as will be shown. Deboronation of some 1,2-C2B10H12 derivatives can be accomplished without strong bases, depending on the attached functional groups. Carbon-bound electron-withdrawing substituents such as C(O)R (R ¼ H or Me) [95], sulfoxide [96], XC6H4 (X ¼ F or NO2) [97] and triazinyl [98] induce their rapid conversion to the nido-carborane in wet DMSO at room temperature; the 1-alanine derivative self-degrades in water [99]. Remarkably, 1-lactose-o-carborane is degraded to the nido-7,8-ðlactoseÞC2 B9 H10
in neutral aqueous solution [100]. The dianions (C2B10H10)2[m-7,8-S 2]22
(n ¼ 1, 2), in which two carborane cages are linked by two 2 2S(CH2)nS2 2 bridges, are converted to (CH2)nS2 2]22
by treatment with 1,2-CH2Br2 in ethanol [101]. Similarly, 1,2-S2 C2 B10 H10 2
(nido-C2B9H10)2[m-7,8-S(CH2)nS2 forms nido-7,8-ðHSÞ2 C2 B9 H10 2
when refluxed with NaI in ethanol [102]. Conversion of C-imido and C-phosphino 1,2-C2B10H12 carborane derivatives to their C2B9 analogues has been achieved by refluxing them in methanol and ethanol respectively [103,104], and dihydropyridyl o-carboranes are deboronated by alcoholic I2 [105]. Partial degradation of C,C0 -bis(phosphino) C2B10 derivatives is promoted by transition metal reagents in alcoholic media, thereby allowing the preparation of metal complexes of nido-7,8-(R3P)2C2B9H10-type ligands directly from 1,2-C2B10H12 carboranes [104,106–111]. Nido-7,8-C2 B9 H12
can also be prepared by the degradation of the so-called “reactive” isomer of the nidoC2 B10 H13
anion 7-4 described earlier, with strong oxidants such as aqueous H2O2 [112]. Treatment of 7-4 with aqueous FeCl3 and SMe2 yields nido-7,8-C2B9H11-9-SMe2 [112].

7.2.2.2 Direct synthesis of nido-7,8-C2B9H12
from B10H14 or B10H13
The Brellochs reaction, described in Chapter 6 for the preparation of CB10 carboranes via the insertion of aldehydes into the decaborane(14) cage, can also be used to generate nido-7,8-C2 B9 H12
in good yields via the reaction of B10H14 with excess formaldehyde in strongly alkaline media [113]. The obvious advantage of this approach is that it yields the parent

7.2 11-Vertex open clusters

227

nido-carborane anion directly from decaborane in a single step. On the other hand, its application in the preparation of substituted derivatives or other nido-C2B9 cage isomers has not been demonstrated. Two-carbon insertions into B10 H13
with loss of one boron atom have been accomplished via reactions of 3-butyne-2-one or methyl propiolate, forming [RC(O)]C2 B9 H11
(R ¼ Me or MeO) with good yields [114].

7.2.2.3 Synthesis of nido-7,9-C2B9H12
derivatives from closo-C2B9H11 Although the most practical route to nido-7,9-C2B9 cluster synthesis is the base-promoted degradation of 1,7-C2B10H12 as described above, other approaches are also available. Treatment of the 11-vertex closo-carborane 2,3-C2B9H11, whose carbon atoms occupy nonadjacent vertices (Figure 1-1 and Section 7.3), with BH4
ion opens the cage to generate nido-7,9-C2 B9 H12
[115]; the same carborane reacts with alkyllithium reagents [115] or dimethyl sulfide [49] to yield nido-7,9-C2B9H11-9-L (L ¼ Me, n-C4H9), and nido-7,9-C2B9H11-10-SMe2 respectively. Other Lewis bases combine with 2,3-C2B9H11 to form similar nido-7,9-C2B9H11L adducts [116].

7.2.2.4 Synthesis of nido-C2B9H13 isomers

Acidification of nido-7,8-C2 B9 H12
with HCl affords neutral 7,8-C2B9H13 (Figure 7-3A) [45], a procedure that has been modified [117] by using H3PO4 in place of HCl. The 7,9-C2B9H13 isomer has not been isolated, a fact that may reflect the absence of an available location for a second B2 2H2 2B bridge on the open face of 7,9-C2 B9 H12
. Protonation of 7,9
0 RR C2 B9 H10 anions at ambient temperature leads to cage closure, generating closo-RR0 C2B9H9 products (Figure 7-3B) [118]. (Nido-7,9-RC2 B9 H11
, where R is H or Ph, is also converted to closo-RC2B9H10 and H2 via reaction with polyphosphoric acid at 70  C, as found in early work [116]). A third isomer, 2,9-C2B9H13, is obtained on protonation of the 2,9-C2 B9 H12
ion (Figure 7-2) [90,91], and substituted derivatives of a fourth, 2,7-C2B9H13, are obtained upon reaction of 7,8-C2 B9 H11 2
with alkyl halides (see below). As noted earlier, 7,8- and 2,9-C2B9H13 are the only isomers of this nido-carborane system to have been isolated and characterized in parent form.

−

H

B B

C B

B R B

H

H

B C

B R

B

H

B

B

B

B

7,8-RRC2B9H11

B = BH

B C

B B

B B

B

B

R R

C

C B B

H+

B B

B

B

B

B

H

B C

R

B

7,8-RRC2B9H−10

R

B

R

B

A

B C

C

+

7,9-RRC2B9H−10

B

B B B

B

2,3-RRC2B9H9

FIGURE 7-3 Protonation of 7,8-RR0 C2 B9 H10
and 7,9-RR0 C2 B9 H10
. R ¼ R0 ¼ H, Me, Ph.

R

228

CHAPTER 7 Eleven-vertex carboranes

7.2.2.5 Synthesis of nido-C2B9H112
(dicarbollide) anions

Deprotonation of the nido-C2 B9 H12
anions in solution generates the corresponding C2 B9 H11 2
dianions (Figure 7-2), which were given the trivial name dicarbollide (from the Spanish olla, jar) by their discoverer, M. F. Hawthorne, in recognition of their open molecular structures. As they lack bridging hydrogens and present clean, unimpeded open faces for complexation to metals, they are electronically analogous to cyclopentadeneide ions (C5 R5
) but are considerably more versatile, and are the foundation of the enormous and highly developed field of icosahedral metallacarborane chemistry (Chapters 12 and 13). The dicarbollide ions are usually employed in situ in complexation reactions with metal reagents, and have been little investigated as species in their own right, in contrast to the well-characterized nido-R2 C2 B4 H4 2
dianions that are discussed in Chapter 4. However, detailed NMR studies of the alkali metal salts of the 7,8-, 7,9-, and 2,9-C2 B9 H11 2
dicarbollide ions in various solvents reveal that they exist in solution as closely associated Mþ C2 B9 H11 2
ion pairs in which the metal is located over the open face, in effect completing the icosahedron [119]. The metal-insertion chemistry of these species is covered in Chapters 13 and 14.

7.2.2.6 Structural studies of nido-C2B9 cage systems

X-ray diffraction data are available for salts of the 2,7-, 2,9-, 7,8-, and 7,9-C2 B9 H12
, as well as C2 B9 H11 2
anions, and for substituted derivatives of these anions and neutral C2B9H13 (Tables 7-2–7-4). No crystallographic studies have been reported for any parent C2B9H13 isomer, but the structure of 2,9-C2B9H13 has been determined by gas-phase electron diffraction [120]. In addition, hundreds of face-coordinated metal complexes containing C2 B9 H11 2
ligands have been crystallographically characterized (Chapter 13, Table 13-3). Although the 11-vertex icosahedral-fragment geometry of the nido-C2B9 cages is well supported by X-ray diffraction, multinuclear NMR, and other data, the location of the “extra” (non-terminal) hydrogen atom in 7,8-C2 B9 H12
and its derivatives has proven elusive. Depending on the cation, the solvent, and/or substituents on the cage, this hydrogen can occupy an asymmetrical bridging position, as in 7-11, or a symmetrical endo-terminal location on B(10) (7-12), or may exhibit fluxional behavior, tautomerizing between these positions, as suggested by NMR evidence and ab initio calculations [121,122]. −

− 10

11

B

9B

7-11

5

B 4B

C 8

H

H

6

B 3

B B1

B C 7

B

B C

B C

7-12

B2

B

B B

B = BH C = CH

B

B B

X-ray diffraction and multinuclear NMR investigations [123] of (Me2SO)2Hþ 7,8-C2 B9 H12
support a symmetrical non-bridged 7-12 structure, both in the solid state and in CD2Cl2 solution, as does a COSY (2d) NMR investigation of the Csþ salt in CD2Cl2 solution [124]. Extended Hu¨ckel molecular orbital calculations indicate that the endo-H interacts with all three borons on the open face via a 4-center 2-electron bond [123]. The 7-12 geometry is also found in the solid state in the zwitterionic 7-mono- and 7,8-dipyridyl derivatives of 7,8-C2 B9 H12
[125], in Csþ7,8-C2B9H19-9,10,11-Me3
[126], and in 7,8-C2B9H11-10-S(CH2)4 [127]. In NMe4 þ PhC2 B9 H11
, the extra hydrogen resides approximately above the center of the C2B3 open face and, in fact, is slightly closer to the carbon atoms than to the boron atoms [128]. 2H2 2B structure 7-11 Crystallographic studies of other substituted derivatives of 7,8-C2 B9 H12
show the bridged B2 [76,107,127,129–137], as does a neutron diffraction study of the proton sponge [1,8-bis(dimethylaminonaphthalene)] salt of parent 7,8-C2 B9 H12
[138] (in some cases, the “extra” hydrogen has not been located). The preferred location for the extra hydrogen can be affected by minor electronic perturbations. For example, in 7,8-C2B9H11-9-I
, the electronegative Iþ substituent induces a 7-11-type geometry with a B(10)-H-B(11) bridge, while in the diiodo 7,8-C2B9H109,11-I2
anion, the structure is that of 7-12, with an endo hydrogen on the molecular mirror plane [135], as expected given the two symmetrically placed iodines. In HNMe3 þ 7,8-C2B9H11-3-I
, which contains an iodo substituent on B(3) [antipodal to B(10)], an intermediate situation is found in which there is an unsymmetrical B2 2H2 2B bridge ˚ from B(10) and 1.37(10) A ˚ from B(9) [139]. between B(9) and B(10), with the hydrogen located 1.17(10) A

7.2 11-Vertex open clusters

229

NMR data on 7,8-C2 B9 H12
and its derivatives in solution have been interpreted in terms of hydrogen tautomerism between equivalent B2 2H2 2B bridging locations on the open face in 7-11 [121,122,138, 140–142], or, alternatively, as a static 7-12-type structure [124]. There is evidence that in derivatives containing a strong electron-accepting substituent, equilibrium favors the tautomer in which the bridging hydrogen is furthest from the substituted boron atom [142]. Clearly, the bridged and non-bridged arrangements are very close in energy, and in solution it may be difficult to distinguish between a rigid, nonfluxional 7-12 geometry and a time-averaged structure of B2 2H2 2B bridged enantiomers. The structures of 7,9- and 2,9-C2 B9 H12
, shown in Figure 7-2, have been established by X-ray diffraction studies on their PSHþ (proton sponge) salts and correspond to those calculated by ab initio molecular orbital methods [90]; the structure of [(Me2N)3PN]2BN(H)PðNMe2 Þ3 þ 7,9-C2 B9 H12
has also been reported [75]. Both carborane anions exhibit mirror symmetry, with the B2 2H2 2B bridge in each case straddling the molecular mirror plane. Crystallographic analyses and extensive NMR data are also available for a number of derivatives of 7,9-, 2,7-, and 2,9-C2 B9 H12
(Tables 7-3 and 7-4).

7.2.2.7 Introduction of substituents: halogenation and deuteration In comparison to the closo-C2B10 systems and many other polyhedral carboranes, the nido-C2B9 species are highly reactive owing to their open-cage structures and the presence of active bridging or endo hydrogens on the 5-membered open face. This fact both facilitates and complicates the placement of functional groups on the cage. C-substituted derivatives of the C2B9H13 and C2 B9 H12
systems are usually obtained by deboronation of the corresponding closo-C2B10H12 derivatives as described above. This approach can also be employed with B-substituted derivatives, provided that the borons to be extracted (those adjacent to both cage carbons in 1,2- and 1,7-C2B10H12) do not have attached groups that block the base attack. Tables 7-2–7-4 list the isolated and characterized derivatives of the 7,8-, 7,9-, 2,7-, 2,8-, and 2,9-nido-C2B9 neutral and anionic carboranes. Deuterium exchange of the anion or neutral 7,8-C2B9H13 with D2O yields B-deuterated products [141,143]; under basic conditions, only the bridging hydrogens are exchanged, but in acidic media some deuteration at the terminal B-H atoms can be observed. The 7,8-C2 B9 H12
anion is easily halogenated by reaction with I2 in aqueous ethanol, affording C2B9H11-9-I
and C2B9H10-9,11-I2
via nucleophilic attack of the formal Iþ at the most electron-rich [{B(9), B(11)] locations [135,144,145]. The C,C0 -diphenyl mono- and diiodo analogues are similarly prepared [146]. Reaction of 7,8-C2 B9 H12
with N-halosuccinimides generates the dihalo products C2B9H10-9,11-X2
(X ¼ Cl, Br, I) in good yield [147], and monoiodo and monobromo derivatives can be obtained via electrochemical methods [148,149]. Adducts of the type 7,8-C2B9H10-9-L, where L is pyridine or a pyridine-type base, react with Br2 to produce 7,8C2B9H10-5(6)-Br-9-L products; here the electron-donating substituent alters the charge distribution in the cage such that the attack of electrophilic Brþ occurs at B(5) or its equivalent B(6) [150]. However, Br2 in acid media and in oxidants such as aqueous FeCl2 destroys the cage framework in 7,8-and 7,9-C2 B9 H12
. [177,553] Many other B-halogenated products have been generated by deboronation of B-halo icosahedral carboranes (Tables 7-2 and 7-3) [52,64,81,139,143,145,151–155], including a per-B-iodinated dicarbollide ion, H2 C2 B9 I9 2
. [415] Attack of the deboronating reagent (n-C4H9)4NþBF4
on 1,7-RR0 C2B10H10 (R, R0 ¼ Me, Ph, 4-FC6H4) results in both boron extraction and fluorination, yielding nido-7,9-RR0 C2B9H9-n-F products (n ¼ 3,10) [82]. B-iodo derivatives of 7,8-C2 B9 H12
, obtained upon reaction of 1,2-C2B10H12 with piperidine, are reported [154] to undergo rapid exchange with Na131I although this has been disputed [156]. At the time of writing this chapter, no halogenated derivatives of nido-C2B9 carboranes other than the 7,8 and 7,9 isomers have been reported.

7.2.2.8 Alkylation, protonation, and cage rearrangement Treatment of the 7,8- and 7,9-C2 B9 H11 2
(dicarbollide) dianions with alkyl halides (RX; R ¼ Me, Et, n-Bu, CH2¼CHMe; X ¼ halogen) produces 7,8-C2B9H11-9-R
and 7,9-C2B9H11-10-R
as isolable products, via electrophilic attack of formal Rþ at a B-B edge on the open face [157–160]. The methylation of 7,9-C2 B9 H11 2
with MeI in THF/ 2C2 2B-bridged intermediate, 7,9-C2B9H9-m(10,11)-Me
, NH3 is proposed, from spectroscopic data, to proceed via a B2 that subsequently rearranges to the terminal B(10)-Me product [160]. Further reaction generates di- and tri-B-methylated species, 7,9-C2B9H10-(n,10)-Me2
(n ¼ 8, 11) and 7,9-C2B9H9-8,10,11-Me3
, in all of which the alkyl groups are bonded only to the boron atoms on the open face.

230

CHAPTER 7 Eleven-vertex carboranes

The alkylation of 7,8-C2 B9 H11 2
by RX reagents and the protonation of the resulting products constitute a mechanistically complex system. When the alkylation is conducted in cold (<0  C) THF, water, or alcohols, it is accompanied by a structural rearrangement of the C2B9 framework to form derivatives of a new cage isomer, 2,7-C2B9H11-11-R
(R ¼ Me, Et, n-C4H9, CH2CH5 5CH2) in which only one of the two framework carbons resides on the open face (Figure 7-4). These species can be reversibly protonated to give neutral 2,7-C2B9H12-11-R carboranes [158,161,162], whose cage structure has been crystallographically established in 2,7-C2B9H12-11-Me [163] and 2,7-Me2C2B9H10-11CH2Ph [161], and investigated via infrared and Raman spectroscopy [164]. The 2,7-C2B9H11-11-R
anions isomerize at 20  C to form 7,9-C2B9H12-8-R
salts. In turn, protonation of the latter species with aqueous acetic acid in hexane at 20  C initiates cage rearrangement that leads to the formation of neutral 2,7-C2B9H12-11-R [161]; treatment with dilute aqueous NH3 regenerates the 7,9 isomer, as shown [161]. The reaction of propargyl bromide with 7,8-C2 B9 H11 2
in liquid ammonia similarly generates 2,7-C2B9H11-11CH
, which on evaporation of the ammonia and heating to 40  C yields 7,9-C2B9H12-8-CH2C CH
; however, CH2C if the liquid ammonia reaction is conducted in the presence of NaNH2 or another strong base, the initial product 2,7CH
rearranges to form 7,8-C2B9H12-9-CH2C CH
[165]. Benzylation of 7,8-C2 B9 H11 2
with C2B9H11-11-CH2C PhCH2Cl, p-BrC6H4CH2Br, or MeC6H4CH2Br isomers under similar conditions yields the corresponding 7,8-C2B9H119-L
derivatives as the final products; intermediate species have not been identified [166,167]. These carborane skeletal rearrangements are remarkable in several respects. They occur under unusually mild conditions (in general, cage isomerizations of open-cluster systems require elevated temperatures), involve open-cage species rather than closed polyhedra, and entail the movement of a carbon atom from a low-coordinate edge position to a highcoordinate location away from the open face. Moreover, cage isomerization promoted by alkylation and protonation is rare although there are such examples in tetracarbon carborane chemistry (see Chapter 11). The mechanism of interconversion of 7,8, 2,7, and 7,9 isomers has not been studied in detail, but the 7,9 ! 2,7 protonation-induced rearrangement is 2− 10 9

B

11

B

B C

5

C

6

R+X−

B

B 4B

B

11

7 4

C

5

B B

2

8

H+

R

B

B 3B

B6

−

B

9

C

4

B

8

5

C

6

B1

aq. NH3

20° C

H

H+

10

B2

B B1

−

11

B B

8

9 6

3

B6

2

C

2,7-C2B9H12-11-R

B

B 4B

B 7 C

5

C

2

B

B 5B

4

C B

7

R

B3

B B1

−

7,8-C2B9H11-9-R

B B

B

B

3

C

11

B

11

7

H 10

10

B

B

−H+

2,7-C2B9H11-11-R− 1) − H+ 2) + H+

H

9

B1

B1 2− 7,8-C2B9H11

R

H 10

B

0° C

B2

3

B

H

9 8

7

8

−

B = BH C = CH

7,9-C2B9H11-8-R−

FIGURE 7-4 Electrophilic alkylation of 7,8-C2 B9 H11 2
and subsequent protonation and cage rearrangement reactions.

R

7.2 11-Vertex open clusters

231

clearly driven, at least in part, by the ability of the latter isomer to accommodate two B2 2H2 2B bridges vs. just one for the 7,9 system [161]. The effects of symmetry via the skeletal electronic structure have also been discussed [168]. H

B = BH C = CH

H H

C

B

10

B

9

C

6

C B

8 2

B

MeI −

B

B 5B

B

7

−I

B3

4

−

−

2− 11

Me

C B

C B

B B

B B

20 °C

B

B

B

B B

B

2− 7,9-C2B9H11

C

B B

B

B B1

C B

7,9-C2B9H11-10-Me−

7,9-C2B9H11-µ-Me−

FIGURE 7-5 Methylation of 7,9-C2 B9 H11 2
with MeI.

Similar driving forces may be at work in the alkylation/protonation of 7,9-C2 B9 H11 2
in which alkyl-bridged intermediates are involved. Treatment with methyl iodide in cold THF affords a CH3-bridged species in which the carbon binds to two boron atoms on the open face via a B2 2C2 2B 3-center bond (Figure 7-5). At room temperature, this species rearranges to the stable product 7,9-C2B9H11-10-Me
[160]. However, when substituents are present on B(10) and B(11), as in 7,9-C2B9H9-8,10,11-Me3
, the alkyl-bridged anion that is formed on methylation is stable at room temperature (Figure 7-6). Reactions of this anion with nucleophiles such as NH2OH and OH are reported to H

Me Me

2−

11

10

B = B, BH C = CH

B B

8

9

C

6

2

C B

B

B

7

MeI Me

−I

B

5

11 8

9 6

B

C

2

B 4

9

B

2

C B

7

20 °C Me

B3

B

7,9-C2B9H8-8,10,11,µ-Me−4 L− = NH2−, OH−

H

6

C H C

B B

B

:L−

H H

B

1

B

10

B1

7,9-C2B9H8-8,10,11-Me2− 3

B

Me

5B

B1

4

Me

−

H

C

−

B3

4

5B

H

8

H2O B

7

B

3

6,8-C2B7H12-7-Me

FIGURE 7-6 Methylation of 7,9-C2B9H9-8,10,11-Me3
.

Me

[7,9-C2B9H8-8,10,10,11-Me4-11-L2−]

N.R.

232

CHAPTER 7 Eleven-vertex carboranes

open the 3-center bond, generating a proposed intermediate, arachno-7,9-C2B9H11-11-L-8,10,10,11-Me4 2
(a structural analogue of the unknown C2B9H15), which undergoes cage degradation on hydrolysis to form arachno-6,8C2B7H12-7-Me (Figure 7-6) [160]. Hydrocarbon substituents can be introduced at B(5) and B(9) in nido-7,8-C2 B9 H12
via palladium-catalyzed crosscoupling of the iodo derivatives with organomagnesium reagents, a method that is widely employed for derivitization of icosahedral carboranes (Chapters 8–10). The actual species that undergo the cross-coupling are dicarbollide ions that are formed by deprotonation with RMgX [169]: THF

7; 8-C2 B9 H11 -n-I
þ RMgX




! 7; 8-C2 B9 H10 -n-I2
þ MgXþ
RH

RMgX;PdðPPh3 Þ4

7; 8-C2 B9 H10 -n-I2


































! 7; 8-C2 B9 H11 -n-R
n ¼ 5;9;

X ¼ Br;I;

R ¼ Me; Et; C6 H13 ; Ph; CH5 5CHCH2 THF

2
þ 7; 8-C2 B9 H10 -5; 9-I
2 þ RMgX




! 7; 8-C2 B9 H9 -5; 9-I2 þ MgX
RH

RMgX;PdðPPh3 Þ4


7; 8-C2 B9 H9 -5; 9-I2
2














! 7; 8-C2 B9 H9 -5; 9-R2 X ¼ Br;I;

R ¼ Me;Et;CH2 Ph

7.2.2.9 Introduction of functional groups of the main-group elements Derivatives of nido-C2B9 carboranes have several important applications, two being especially noteworthy: the designed synthesis of compounds for medical applications such as boron neutron capture therapy (BNCT, described in Chapter 16), and the development of charge-compensated carborane ligands [170,171] to replace Z5-C5 H5
(Cp
) in metal sandwich compounds. In the latter case, the dinegative charge on the C2 B9 H11 2
(carbollide) ion is reduced to
1 by replacement of a neutral B2 2H hydrogen atom with a positively charged substituent such as SMe2 þ to create a nido-C2B9H10L
ligand that is isoelectronic and isolobal with Cp
. This allows, for example, the synthesis of sandwich complexes of the type FeII[C2B9H10(SMe2)]2 that are electronic analogues of ferrocene. The idea of charge-compensation in these metallacarboranes is further examined in Chapter 13. Several methods are available for the preparation of nido-C2B9 clusters that have attached organic and organometallic groups, one of which is the deboronation of B-substituted closo-C2B10 carboranes as described above. A more direct approach involves metal ion-promoted oxidative coupling of a Lewis base to the monoanion [170,172–176]: nþ ! 7; 8-C2 B9 H11 L þ Mðn
1Þþ 7; 8-C2 B9 H
12 þ L þ M

When FeCl3 is employed as the metal reagent, nido-7,8-C2B9H11-9-L (asymmetric) and/or nido-7,8-C2B9H11-10-L (symmetric) isomers are obtained, where L is an amine, pyridine, dialkyl sulfide, pyridine, OEt2, PPh3, or other electron donor; however, in some cases, yields are lower because of a competing reaction that leads to bis(dicarbollyl)iron complexes [170]. This occurs when the base—for example, triethylamine—is sufficiently strong to deprotonate the C2 B9 H12
substrate and convert it to C2 B9 H11 2
, which in turn combines with Fe2þ to form FeII ðC2 B9 H11 Þ2 2
. The problem can be circumvented by using weaker bases [170] or by employing other metals as oxidants. For example, by using CuSO4 in the reaction with NEt3 metallacarborane formation is avoided and nido-7,8-C2B9H11-9-NEt3 is generated in high yield [133]. HgCl2 and TiCl4 have been similarly employed to prepare pyridine and/or THF adducts [174,176]. A useful route to nido-7,8-C2B9H11-9-SMe3 and nido-7,9-C2B9H11-8-SMe3 synthesis is based on the reaction of the nido7,8- and 7,9-C2 B9 H12
anions with dimethyl sulfoxide in aqueous H2SO4 [49], preferably at 80  C [133,137,177,178]; the (
) enantiomer of 7,8-C2B9H11-9-SMe3 has been partially resolved [179]. Two other isomers, nido-7,8-C2B9H11-n-SMe3 (n ¼ 5 and 7) are generated upon deboronation of closo-(HS)C2B10H11 and closo-C2B10H11-9-SH, respectively, with

7.2 11-Vertex open clusters

233

KOH in methanol followed by methylation with MeI [49]. A different approach, electrochemical thiocyanation, affords 9-SCN derivatives [180]: electrolysis; Pt anode


7; 8-R2 C2 B9 H
10














! 7; 8-R2 C2 B9 H9 -9-SCN

R ¼ H; Me

KSCN;MeOH

Treatment of the 7,8-C2 B9 H12
anion with dialkyl sulfides and formaldehyde in aqueous acid gives 7,8-C2B9H12-9CH2SR2 derivatives in good yields, presumably via intermediates arising from protonation of HC(O)H, together with small amounts of 7,8-C2B9H12-10-SR2 products [181]. Formaldehyde and dialkyl ethers, on the other hand, primarily yield the arachno-carborane C2B7H13, described earlier in Section 5.6, along with low yields of 10-OR2 derivatives [182–184]. When formaldehyde is replaced by acetaldehyde, the results are quite different: MeC(O)H and 7,8-C2 B9 H12
alone generate 7,8-C2B9H12-10-OEt2 and 7,8-C2B9H12-10-10-OH, but in the presence of bases one obtains 7,8-C2B9H12-10-L products in high yields [181,185,186]. These transformations, summarized in Figure 7-7, are highly dependent on reaction conditions, especially the solvent, acid strength and, of course, the nature of the base, and have been studied in some detail. The fluxional tautomerizing behavior of the “extra” hydrogen, described earlier in this Section, is proposed to account for the observed substitution patterns [181]. If the incoming group attacks the B2 2H2 2B bridged tautomer 7-11 at the open B-B edge, it can exchange with the terminal hydrogen on B(9) to generate a B(9)-L product; conversely, if the endo-hydrogen in 7-12 is first removed (as in the action of a strong base), a vacant orbital on B(10) is generated and this can lead to B(10)-substitution. Factors such as the electronegativity and steric bulk of the attacking group determine which of these pathways predominates in a particular case. A different approach to the synthesis of B(10)-substituted derivatives the ring-opening of 7,8-C2B9H12-B(10)-cyclic oxonium derivatives with K2CO3 to give benzoic acid or azide products [187]. 10

L

B = B, BH C = CH −

7,8-C2B9H12

L = R2O

H3O+ + MeC(O)H

B

B 4B

10

B C

9

7

8

5

C

6

B 3

B

B 2

B B1

7,8-C2B9H11-10-R R = OH−, OEt2

6

B

10 9

B

B

8

B 4B 11

B

B 4B

B C

B

C

6

B 3

B

11

B C

7

C

6

B 3

B

+

6,7-C2B7H13

2

(major)

B B1

7

8 5

2

B

3

L

L 11

B C

B1

R 9

C

7,8-C2B9H11-9-L

5

B

11 7

+ HC(O)H

+L

10

8 5

L H3O+ + MeC(O)H

B

B 4B

L = R2S H3O+

9

B

2

7,8-C2B9H11-10-L (minor)

B B1

7,8-C2B9H11-10-L (major) L = SMe2, SEt2, S(CH2)4, O(CH2)2S, OEt2, (CH2)4O, O(CH2)2O

FIGURE 7-7 Reactions of nido-7,8-C2 B9 H12
ion with Lewis bases in acid media.

234

CHAPTER 7 Eleven-vertex carboranes HO-C6 H4 -CðOÞOH 7; 8-C2 B9 H11 -10-OC4 H8














! 7; 8-C2 B9 H11 -10-OðCH2 Þ4 O-CðOÞO
K2 CO3

NaN3

7; 8-C2 B9 H11 -10-OC4 H8




! 7; 8-C2 B9 H11 -10-OðCH2 Þ4 -N3 EtOH

Other methods employed for direct B-functionalization of nido-7,8-C2 B9 H12
or its substituted derivatives include acylation with RC(O)Cl or [RC(O)]2O in benzene-THF to form 7,8-C2B9H12-9-C(O)R (R ¼ Me or Ph) [188], and the reaction of 7,8-C2B9H12-9-CH2SMe2 with pyridine to generate 7,8-C2B9H10-9-Me-11-NC5H5 (7-13). In the latter reaction, the interesting net effect is that pyridine is added at B(11), while the SMe2 group is displaced by a hydrogen atom, leaving a methyl substituent on B(9) [181]: H

B

Me2SiCH2

H

B C

B C

pyridine

B

Me

C

B

B

B

B

B

B

B C

B

B

B

B

NC5H5

7-13

B B

B

The asymmetric cyclic monothioether 7-14, prepared by deboronation of closo-1,2-[cyclo-S(CH2)3]-C2B10H10, when treated with PdCl2(PPh2R)2 (R ¼ Ph or Me) in boiling ethanol acquires a phosphino substituent at B(11) to form nido7,8-[cyclo-S(CH2)3]C2B9H9-11-PPh2R (7-15) [189]. Under other conditions, 7-14 combines with organotransition metal reagents to form icosahedral 12-vertex metallacarboranes or complexes of the exo-nido type in which the metal resides outside the carborane framework (see Chapter 13). S C

S

− C

B B

B B

B B

B

B

PdCl2(PPh2R)2

EtOH B = BH

C

C

B B

B B

B B

PPh2R R = Ph, Me

B

B

B

B

7-14

7-15

Reactions of dicarbollide salts have been employed to generate derivatives having B2 2MIV bonds where MIV is Ge or Sn; e.g., treatment of Tl2C2B9H11 with Ph3MCl in MeCN yields nido-7,8-C2B9H10-10-MIV Ph3
[190]. Similarly, reactions of 7,8-C2 B9 H11 2
with organophosphorus and organosilicon reagents in THF give nido-7,8-C2B9H10-9-R products, where R is SiPhMe2, SiMe3, PPh2H, or PPh3 [191]. Phosphino groups can also be added by treatment of PPh2Cl with 7,8-C2 B9 H12
to give nido-7,8-C2B9H10-9-PPh2H [312] and also via the reaction of Tlþcloso-Tl(C2B9H11)
with PPh3 over AgBr to yield 7,8-C2B9H10-9-PPh3 [192]. Aluminum-, gallium-, thallium-, and mercury-containing derivatives are also obtainable. Reactions of neutral nido-7,8-C2B9H13 with MR3 (M ¼ Al or Ga, R ¼ Me, Et) generate both nido-7,8-C2B9H12-m(9,10)-MR2 products 2H2 2B bridges on and closo-RM(C2B9H11) metallacarboranes [193]; in the former case the metal is attached via M2 the open face, while in the latter species, the metal is fully incorporated into the cage and completes the icosahedron, as discussed in Chapter 13. Similar to these are the highly versatile MC2B9 complexes of Al, Ga, or In, described in Chapter 12, in which an amino group is tethered to the cage via one or more CH2 units and stabilized by an aminemetal linkage [194]. Treatment of Tlþcloso-Tl(C2B9H11)
with HgCl2(PPh3)2 or other mercury reagents yields nido-7,8-C2B9H11-10-R 2B single bond [195]. An X-ray structure [R ¼ Hg(PPh3), Me, Ph] in which the mercury is bound to B(10) via an Hg2 determination of nido-7,8-C2B9H11-10-Hg(PPh3) (7-16) [195] reveals that the metal atom is located directly above

7.2 11-Vertex open clusters

235

B(10), forming a linear P2 2Hg2 2B array, a geometry that can be correlated with the saturated electronic valence shell of mercury. Analogous copper and gold complexes have been similarly prepared (Table 7-2) [195].

P

Hg

7-16 B

C

B = BH C = CH

B B

C

B

B B

B

B B

In addition to those prepared via direct attachment of functional groups to nido-C2B9 cages, many derivatives containing nitrogen, phosphorus, sulfur, silicon, or other main group elements (Tables 7-2–7-4) have been synthesized by deboronation of their corresponding o-carborane derivatives. Among these are macrocycles of the type m(7,8)SCH2(CH2OCH2)3CH2S-C2 B9 H10
that contain exo-polyhedral chains connected at both ends to the carborane carbon 2O2 2CH2CH22 2S)C2B9H11 can be obtained atoms [196]. Similar macrocyclic compounds such as m(7,8)-(S2 2CH2CH22 directly from closo-1,2-(HS)2C2B10H10 under basic conditions in dilute solution, which minimizes polymer formation [197].

7.2.2.10 Dimers and multicage derivatives Numerous compounds having two or more nido-C2B9 cluster units, either directly bound or linked by an intervening group, are known. In many cases, these are generated by deboronation of the closed-cage (closo) species; for example, the silicon-bridged compound m(9,10)-(C5H5N)2Si(C2B9H11)2 (7-17) was produced by the degradation of the sandwich complex commo-3-Si(1,2-C2B9H11)2 with pyridine [198]. B B B

B B

C C

B

B B B

B

B

C C

B

C C

B B

B B

B

B

NC5H5

B B B

B

Si

2 NC5H5

Si B

B

B

B

B = BH C = CH

NC5H5 B

C C B

B B

B

7-17

B B

B B

B


Oxidation of the 7,8-C2 B9 H12 ion with 1/6 equivalent of chromic acid forms a C4 B18 H23
anion, probably via an initially formed (C2B9H12)2 intermediate [199,200]. When a larger proportion (1/3) of H2CrO4 is employed, the C4 B18 H23
is further oxidized to generate neutral neo-C4B18H22 (7-18), together with very small amounts of a second isomer, iso-C4B18H22 (7-19); the latter compound can be obtained in larger yields by the thermolysis of neutral 7,8C2B9H13 at 80  C in benzene or toluene [201]. X-ray crystallographic [202–204] and detailed NMR [199,201,202] studies of these carborane dimers have established the structures shown here, which are quite dissimilar: 7-18 contains

236

CHAPTER 7 Eleven-vertex carboranes

identical nido-7,8-C2B9H11 units joined by two 2-electron, 3-center (2e3c) bonds involving B(9) and B(10) on the open faces, while 7-19 consists of closo-1,2-C2B10H11 (o-carboranyl) and nido-5,6-C2B8H11 cages linked by a single 2-center B
B interaction. C

B

7-18

B

B

B

B

H

B

B

B

B

B

B

C

B

B

B

iso-C4B18H22

B B

B

B

B B

B =B B = BH C = CH

B

C

H

C

C

B B

B

neo-C4B18H22 B

B

B

B

7-19

B

C

H

B

B

B

B B

B C

H

C

B

The dimer 7-18 reacts with Lewis bases, severing the intercage connection and forming monomeric nido-7,8C2B9H11-L adducts [199]: 0:5C4 B18 H22 þ L ! 7; 8-R2 C2 B9 H9 -n-L;

n ¼ 9; 10;

L ¼ OEt2 ; OC4 H8 ; SMe2

Here, the driving force is evidently the formation of strong 2e2c B2 2L bonds, with the attacking bases replacing the weaker 2e3c inter-cluster binding in 7-18. As expected from the presence of two BHB bridging protons, 7-18 is a dibasic acid with pKa1 ¼ pKa2 ¼ 2.4. Its conjugate base dianion, C4 B18 H20 2
on reduction with sodium in liquid ammonia, forms C4 B18 H20 4
, which readily acquires two protons to form C4 B18 H22 2
(7-20); protonation of this species regenerates the same C4 B18 H23
monoanion (7-21) that is obtained when 7,8-C2 B9 H12
is oxidized by chromic acid as described above [199]. The structures shown are based on NMR evidence [199]. In each of these dimers, the fact that intercage binding occurs only between the borons located on the open faces correlates with the high electron density that is associated with these atoms. Other C4 B18 H23
and C4 B18 H22 2
anions, prepared by deboronation of one or both cages of 1,10 -(closo-1,22C intercage linkages of their precursors [205]. C2B10H11)2 dimers, retain the C2 B =B B = BH C = CH

B B B B C

B B

B B H

B B B

2− B B

C

B C

H

B C

B C B

B B

B

B B

B B H

C

− B

H

B

H

C B

B B

B B

B B

B

7-20

B C

B

7-21

The versatility of anionic nido-C2B9 carboranes, with their open faces and amenability to metal complexation, affinity for water and other polar solvents, and generally high stability, has prompted the synthesis of a wide variety of derivatives for a range of possible applications (Chapters 14–17). In many of these compounds, listed in Tables 7-2 and 7-3, two or more nido-7,8-C2B9 cages are connected by various linking groups. Among these are disulfide-bridged species

7.2 11-Vertex open clusters

237

such as 7-22, obtained by deboronation of S2(1,2-RC2B10H10)2 with piperidine in EtOH [206], and doubly-bridged macrocycles like 7-23, prepared by reacting nido-ðHSÞ2 C2 B9 H10
with I3
in water [207]. Related compounds having 2 and 2 2SCH22 2C6Hn2 2CH2S2 2 linkages are also known [101,208]. 2 2S(CH2)nS2 −

B B B

R

B B B

−

R C

B

S

C

S

B B

B

B

C

C

B

B

B

B B

B

B

B

B B

S C

S

C

B

B

B

C

S

B B

C

S

B

B

B

R = H, Me, Ph

−

B B

B −

B

B

B

B

B = BH

7-22

7-23

Other variations on this theme include dimers with linked closo-C2B10 and nido-C2B9 units and cage structures connected by single sulfur atoms, thioethers, or other linkers. In the latter category is a family of bis(dicarbollide) tetraanions (7-24, 7-25, 7-26), obtained by deboronation of their corresponding HCB10H10C-L-CB10H10CH linked closocarboranes, that are designed as “Venus flytrap” agents [209] as they are capable of efficiently trapping metal ions via coordination to their open faces as in 7-27. The syntheses of the first such species (7-24, 7-25) [210–212] proved difficult and time-consuming because of the numerous protection and deprotection steps, and have been superseded by the more easily prepared ether- and thioether-linked anions 7-26 [213,214]. The projected application of these and similar bis(dicarbollide) ligands as carriers for radioactive 57Co in tumor therapy and in the scavenging of radioactive transition metals from nuclear waste is discussed in Chapters 16 and 17, respectively. 2−

2− CC

C

C

N

C

O

L = (CH2)n, TsN(CH2}2

L

C

C = C, CH

C

OH

N

C C

2−

2−

7-24

7-25 −

4− CC E C

C

CC

M3+

E

M E = O, S C

C = C, CH

C

M = Cr, Fe,

7-26

Co, Ni

7-27

Notable examples of multicage derivatives that have been designed for boron neutron capture therapy (BNCT) and represent a remarkable synthetic achievement, are the 120-boron complexes B12[O(CH2)6-C2B9H8R]1214
(R ¼ H, Me) whose icosahedral B12 cores are bound to 12 nido-C2B9 cages via oxyhexamethylene chains [215].

238

CHAPTER 7 Eleven-vertex carboranes

7.2.2.11 Transition metal complexes

The nido-C2 B9 H12
and nido-C2 B9 H12 2
ions readily coordinate to metal ions in a variety of modes, ranging from Z1 (attached to one cage atom) to Z5-bonded metallacarboranes in which the metal is centered over the 5-membered open face, with the latter class overwhelmingly predominant. In many cases, suitably functionalized nido-C2B9 ligands for transition metals have been designed for catalytic and other applications. Metallacarborane chemistry has evolved into a huge subfield requiring separate treatment, and is covered in Chapter 13.

7.2.2.12 Reboronation Boron insertion into the open face of nido-C2B9 cages to complete the icosahedron—the reverse of deboronation—can be employed to generate B(3)- and B(6)-substituted derivatives of 1,2-C2B10H12 [47,94,153,216–222], as well as 1,7C2B10H11-2-L compounds [223]. In the reaction sequence shown in Figure 7-8, B(3,6)-diphenyl o-carborane products are obtained via successive boron addition, deboronation, and reboronation steps [94]. The reaction is blocked if substituents are present on both B(3) and B(6), as the remaining BH units are unreactive toward bases. This approach has been employed to synthesize an optically active o-carborane derivative, 1,2-PhC2B10H10-3-p-C6H4Me, by reacting a partially resolved enantiomer of nido-7,8-PhC2 B9 H10 2
with p-MeC6H4BCl2 [224]. A different type of reboronation process is used in the reaction of nido-C2 B9 H12
with triethylamine borane at 200  C, in which boron insertion into the cage is accompanied by the addition of an exo-polyhedral BH3 substituent on one of the cage carbon atoms [219]. The closo-1,2-ðH3 BÞC2 B10 H11
product, in turn, can be converted into a variety of closo-1,2-ðLH2 BÞC2 B10 H11
products, where L is SMe2, NC5H5, NMe3, or NEt3, via treatment with Lewis bases. On treatment with acid followed by heating to 80  C, closo-1,2-ðH3 BÞC2 B10 H11
is quantitatively converted to the parent compound 1,2-C2B10H12 and hydrogen [219].

2− B

B

C C

B B

B B

B

B B

R

R

R

B

B

B

RBCl2 R

B = BH R = H, Me R = Ph, Et

7,8-R2C2B9H92−

B

C C

B B

B B

R R

B

EtO−

B

EtOH

B B

B

B

C C

B B B

R R

−

B H

B

1,2-R2C2B10H9-3-R

1,2-R2C2B10H9-3-R

Ph B B

1,2-R2C2B10H8-3,6-Ph2

B

C C

B B

B B

B

R R

PhBCl2 R = H, Me R = Ph

B Ph

B

FIGURE 7-8 Boron insertion into nido-R2 C2 B9 H10 2
dicarbollide ions to generate closo-1,2-C2B10H12 derivatives, followed by deboronation and a second boron insertion to form B(3,6)-disubstituted products.

7.2 11-Vertex open clusters

239

7.2.2.13 Other properties of nido-C2B9 carboranes

Isomers of neutral C2B9H13 lose hydrogen at 75-100  C and generate closo-2,3-C2B9H11 (Section 7.3) [116,225,226]. The latter carborane is also obtained upon protonation of nido-7,8- and 7,9-C2 B9 H12
at high temperature [18,225], a process that, in the former case, requires a cage framework rearrangement because 2,3-C2B9H11 has nonadjacent carbon atoms; this also occurs during thermal isomerization of 7,8- to 7,9-C2 B9 H12
at 300  C. Rearrangement is also evident in the disintegration of the 7,8- and 7,9- nido-PhC2B9H12 isomers on treatment with chromic acid at 100  C, which affords a mixture of alkynes and other organic products [227,228]. The nature of these compounds, and the fact that similar products are obtained from both isomers, implies that both o- to m-carborane and m- to o-carborane isomerizations take place during oxidative cleavage.

7.2.3 Nido-C3B8H12 and nido-C3B8H11
7.2.3.1 Synthesis Tricarbollide ions (Table 7-5), which are isoelectronic analogues of the nido-C2 B9 H11 2
(dicarbollide) clusters, were first obtained by cyanide insertion into nido-5,6-C2B8H12 to form nido-7,8,9-(H2N)C3 B8 H10
(7-28) and arachno-5,6(NC)C2 B8 H11
[229–231] . Neutral derivatives (7-29) can be prepared by several methods. Methylation of 7-28 with MeI and NaH produces (Me3N)C3B8H11, and the reaction of Me3CNC with arachno-5,6-ðNCÞC2 B8 H11
at room temperature forms [(Me3CNC)H2N]C3B8H11; when Me2SO4 is present, the latter reaction produces [(Me3CNC)MeHN] C3B8H11 [229,230]. The last two carboranes can be converted into (Me3N)C3B8H11 by treatment with MeI and NaH in refluxing glyme, a process that evidently involves elimination of isobutylene.

B

−

−

H

B B

H2N

NaCN

C B

B

C

B

7-29

B B

7-28

B

5,6-C2B8H−11

R

B

B B

B = BH C = CH

B

B C

C C

H2O

B

B

7,8,9-(H2N)C3B8H−10

B C

B C

C

B

B B

B

7,8,9-C3B8H10-R R = NMe3, NHMe2, Me3CNH2, Me3CMeHN

B B

Deamination of nido-7,8,9-(H3N)C3B8H11 with sodium naphthaleneide, followed by aqueous CsOH in THF, preduces the parent nido-7,8,9-C3 B8 H11
ion, and protonation of the latter species with CF3C(O)OH yields neutral nido-7,8,9-C3B8H12 (Figure 7-9) [232]. The corresponding anion can be regenerated from the neutral carborane via deprotonation with strong bases, and the neutral compound can be prepared directly from nido-7,8,9-(7-H3N) C3B8H10, as shown [232]. A more efficient route to nido-7,8,9-C3B8H12 derivatives has been developed, in which a solution of Naþ5,6-C2 B8 H11
in neat Me3CNC is evaporated to dryness and acidified to produce nido-7,8,9-(7-Me3CNH2) C3B8H10 almost quantitatively [233]. The latter compound is treated with AlCl3 to produce nido-7,8,9-(7-H3N) C3B8H10 in 77% yield; this derivative, in turn, can be quantitatively converted to nido-7,8,9-(7-Me3N)C3B8H10 via methylation with alkaline Me2SO4. Treatment of the 7-Me3N species with sodium in liquid ammonia affords nido7,8,9-(7-Me2NH)C3B8H10 and nido-7,8,9C3B8H12 [233].

240

CHAPTER 7 Eleven-vertex carboranes − Me3N

B

C

B B

C

1) Na/THF

C

C

B B

B

2) OH−

B

B B B

B = BH C = CH

1) Na/THF 2) F3C-C(O)OH

B

B

B

B

B 7,8,9-(Me3N)C3B8H10

B

C

C

7,8,9-C3B8H−11

base

F3C-C(O)OH

H

B

C

B

C

C B

B B

7,8,9-C3B8H12

B

B B

FIGURE 7-9 Interconversion of neutral and anionic 7,8,9-C3B8H12 derivatives.

Table 7-5 Nido- and Hypho-C3B8 Derivatives Compound Synthesis and Characterization Nido-C3B8H12 derivatives 7,8,10-LC3B8H10 [L ¼ Me3N, Me3C(Me)HN] 7,8,10-C3B8H10-10-NMe3 7,8,9-C3B8H12 7,8,9-C3 B8 H11
7,8,10-C3 B8 H11
7,8,9/7,8,10-C3 B8 H11
7,8,9-MeC3B8H11 2,7,10-RC3B8H11 (R ¼ PhCH2, Me) (H2N)C3B8H10 7,8,9-(7-Me3N)C3B8H10 Me3CNH2-7,8,9-C3B8H10 7,8,9-LC3B8H10 (L ¼ NH2
, NH2C4H9, NMe3, N(Me3C)MeH, NMe2H) 7,8,9-(RR0 NH)C3B8H10 and (R, R0 ¼ H, H; H, CMe3; Me, Me; Me, CMe3) solvent-dependent tautomerism

Information

References

S, S, S, S, S, S, S, S, S, S, S, S, S,

[554] [232] [232] [231] [231] [234] [232] [232] [237] [231] [231] [231] [229]

X [Me3C(Me)HN], H, B(2d) X, H, B(2d), IR, MS H, B(2d), MS MS H, B, MS H, B(2d) H, B(2d), IR H, B(2d), MS H, B, C H, B H, B, MS H, MS X [N(Me3C)MeH], H, B(2d), IR, MS

S, H, B,C

[239] Continued

7.2 11-Vertex open clusters

241

Table 7-5 Nido- and Hypho-C3B8 Derivatives—Cont’d Compound

Information

References

S, X(H,CMe3), H, B,C

[239] [236] [555] [234] [232] [232] [232] [556] [233] [233] [233] [238]

7,8-(cyclo-CH2OCH2)-7,8,9
C3 B8 H8


S, X(PhCH2), H, B(2d), C(PhCH2) S, H, B, C X, H, B(2d), MS S, H, B(2d), IR, MS S, H, B(2d), IR, MS S, H, B(2d), IR, MS S, H, B(2d) S, H, B(2d), IR, MS S S S (metal-promoted cage rearrangement), X (Me3CHN), B(2d), IR, MS S, H, B, IR

Hypho-C3B8H16 derivatives 2,5,12-C3 B8 H15


S, X, H, B, C, IR, MS

[240]

Other Experimental Studies nido-7,8,9-(Me3N)C3B8H10 nido-7,8,10-RC3 B8 H10
(R ¼ PhCH2, Me) nido-7,8,9-C3 B8 H11
nido-7-L-7,8,9-C3B8H10 (L ¼ H3N, Me3CH2N, Me2HN)

Thermal rearrangement ! 7,8,10 isomer Protonation, cage rearrangement Thermal rearrangement ! 7,8,10 isomer Metal-promoted cage rearrangement

[234] [237] [234] [238]

Theoretical Studies Molecular and electronic structure calculations nido-7,8,9/7,8,10-C3B8H12 nido-C3 B8 H11
isomers nido-7,8,9-(H3N)C3B8H10 hypho-2,5,12-C3 B8 H15


DFT, stability DFT, stability DFT, optimized structure DFT

[244] [244] [239] [240]

Isomerization calculations nido-7,8,9-C3 B8 H11


7,8,9 ! 7,8,10 rearrangement

[235]

NMR calculations nido-7,8,9-C3B8H12 nido-7,8,10-C3 B8 H11
nido-7,8,9-C3 B8 H11
nido-7,8,10-MeC3B8H11 (isomers) hypho-2,5,12
C3 B8 H15


IGLO IGLO IGLO GIAO/IGLO GIAO

[232] [232] [232] [237] [240]

0

0

7,8,9-(RR N)C3B8H11 (R, R ¼ H, H; H, CMe3; Me, Me; Me, CMe3) solvent-dependent tautomerism 7,8,10-RC3 B8 H10
(R ¼ Me, PhCH2) 7,8,9-(Me3C
NH2)C3B8H10 7,8,10-C3B8H10-10-NMe3 7,8,9-(Me3CMeN)C3B8H10-10-Me 7,8,9-(Me3CMeN)C3B8H9-11,12-Me2 7,8,10-(Me2NH)C3B8H10 Tlþ 7,8,9-RC3 B8 H10
(R ¼ H2N, Me3CNH) 7,8,9-C3B8H10-7-NH2C4H9 7,8,9-C3B8H10-7-NR3 (R ¼ H, Me) 7,8,9-C3B8H10-7-NHMe2 8-L-7,8,9-C3B8H11 (L ¼ H2N, Me3CHN, Me2N)

S, synthesis; X, X-ray diffraction; H, 1H NMR; B, spectroscopic data.

11

B NMR; C,

13

[557]

C NMR; 2d, two-dimensional (COSY) NMR; IR, infrared data; MS, mass

242

CHAPTER 7 Eleven-vertex carboranes

7.2.3.2 Cage isomerization

Thermal rearrangement of Csþ nido-7,8,9-(7-L)C3 B8 H10
(L ¼ H or NMe3 þ ) at 350  C generates 7,8,10-(10L)C3 B8 H10
(7-30) [234], reflecting the tendency of the framework carbon atoms to prefer non-vicinal locations in the cage (see Section 2.7). Based on m2-Hu¨ckel MO calculations, a mechanism involving carbon-carbon bond cleavage followed by consecutive diamond-square-diamond (dsd) rearrangements has been proposed [235]. −

B C

− B C

C

B L

350 °C

B

B B

B

L = H,

B

NMe+3

B 7,8,9-(7-L)C3B8H−10

C

L

C B

C

7-30

B

B B

B

B B 7,8,10-(7-L)C3B8H−10

Derivatives of the 7,8,10-C3B8 system can also be prepared by boron insertion into 10-vertex nido-5.6,9-(6R)C3 B7 H9
carboranes, generating 7,8,10-(7-R)C3 B8 H10
anions (7-31) [236]. −

R

C

B C

B

C

B B

B

C

1) Me2SBH2Br

B 5,6,9-(6-R)C3B7H9−

C B

C B

B B

2) proton sponge B = BH C = C, CH R = Me, CH2Ph

B

−

B

R

7-31

B

B B

7,8,10-(7-R)C3B8H−10

Protonation of 7-31 induces yet another cage isomerization, forming 2,7,10-(2-R)C3 B8 H10
(7-32), in which one of the skeletal carbons occupies a normally unfavorable higher-coordinate vertex away from the open face [237]; the process is reversed upon deprotonation of 7-32, which regenerates the 7,8,10 isomer. R

C

−

B

H

C B

C B

B B

B

H2SO4

B

B = BH C = C, CH R = Me, CH2Ph

B 7,8,10-(7-R)C3B8H−10

C B

C B

B B

proton sponge

B

B

7-32

B C R

B

2,7,10-(2-R)C3B8H11

The driving force for this rearrangement, as supported by DFT calculations, is evidently the need to provide a vacant B2 2B edge for the added proton. Similar framework isomerizations resulting from protonation occur in nido-C2B9 systems and have been discussed earlier in this chapter, for example, the conversion of 7,9-C2B9H12-8-R
ions into 2,7-C2B9H12-11-R
isomers. A plausible mechanism that has been suggested [237] for the interconversion of 7-31 and 7-32 involves a shift of just one boron vertex, B(11)-H: B B C

C B

C B

B B

B B B

B C

C

C B

B B

B B B

7.2 11-Vertex open clusters +

− B

L

C C

B C

B B

B B B

B = BH C = C, CH

7,8,9-(7-L)C3B8H10

B

B B

H+

B

C

C

−H+

L

C

B

B

B B

−

B

243

7,8,9-(7-L)C3B8H−10 L = H2N, Me3CNH, Me2N

L = H3N, Me3CNH2, Me2NH

metal cation reflux

−

−

B

C

B

C

C

B

+

C

C

H+

B

B B

C

B

L

B B B

L

B

B B

B B B

7,8,9-(8-L)C3B8H−10

7,8,9-(8-L)C3B8H10

FIGURE 7-10 Metal-induced cage rearrangement in nido-7,8,9-(7-amino)C3B8 derivatives.

A different type of isomerization has been discovered in the course of attempts to prepare metal-tricarbollide sandwich complexes from (amineþ)C3 B8 H10
zwitterions via deprotonation and reaction with metal ions [238]. When FeI2, NiCl2, or Cp2Ni is employed as the metal reagent, no metal complex is obtained; instead, the net result following reprotonation is migration of the amine substituent from C(7) to C(8), as shown in Figure 7-10. A mechanism has been proposed [238] for this rearrangement and it is similar to the 7,8,10 to 2,7,10-RC3 B8 H10
conversion discussed above. However, in this case, it is the C(7)-amino group in 7-33 that swings into the open face, forming 7-34, which has an unfavorable high-coordinate carbon (off the open face) and rearranges to 7-35:

B C

B C

C B

B B

B B B

7-33

L

L

C

C

B

B

C C

L

B

B

B B

B B B

7-34

B

C

C B

B

B

B

B B

7-35

Aminocarboranes of the type nido-7,8,9-(7-NHR2)C3B8H10 exhibit solvent-dependent “absolute” proton tautomerism that may be unique in all of chemistry. In proton-transfer media such as water, ethanol, and acetone, only the zwitterionic form NHR2 þ C3 B8 H10
(7-36) is observed, while in proton-nontransferring solvents such as benzene and other hydrocarbons, only the B2 2H2 2B bridged tautomer (R2N)C3B8H11 (7-37) is detected in detailed multinuclear NMR studies [239].

244

CHAPTER 7 Eleven-vertex carboranes

In MeCN/CDCl3 an equilibrium between 7-36 and 7-37 is observed, with the zwitterion form favored by increasing MeCN concentration. Both tautomers can be isolated as pure crystalline solids and exhibit markedly different NMR spectra and melting points. + R2NH

H

− B C

B C

C

R2N proton-nontransfer solvents

B

B B

B B B

7-36

proton-transfer solvents

C

B

B C

C B

B B

B

B B

7-37

Deprotonation of both 7-36 and 7-37 with proton sponge yields identical (NR2)C3 B8 H10
anions, which on reprotonation afford either 7-36 or 7-37, depending on the solvent used. DFT calculations show that the neutral form 7-37 is more stable by 22 kcal mol
1 compared to the zwitterionic tautomer 7-36, suggesting that the latter is stabilized by the strong interaction with the solvent, which probably involves hydrogen bonding [239].

7.2.3.3 Structures and reactions The icosahedral-fragment geometry of the nido-C3B8 carboranes is well established from NMR spectra and X-ray crystallographic analyses of a number of derivatives (Table 7-5). In the 7,8,9 and 7,8,10 systems the open face deviates slightly from planarity, with the framework carbon atoms displaced slightly toward the lower B5 belt [229,230,236]. Other than the reactivity described in this section, most of the known chemistry of these clusters involves their complexation with metals to form tricarbon metallacarboranes, a topic that is reviewed in Chapter 13.

7.2.3.4 Hypho-C3B8H15
Eleven-vertex arachno-C3B8 carboranes, that is C3B8H14 and its derivatives, are unknown at this writing, but a unique C3B8 hypho-class cluster has been prepared. Deboronation of the zwitterionic compound nido-7,8-C2B9H11-9-CH2SMe2 with a 3:1 excess of aqueous KOH affords hypho-C3 B8 H15
in 32% yield accompanied by an equal amount of hypho7,8-C2 B6 H13
, an 8-vertex species that was described earlier (Section 5.4) [240]. The hypho-C3B8 geometry, which corresponds to a closo 14-vertex polyhedron from which 3 vertexes have been removed, is shown in Figure 7-11(A). The cage structure is slightly distorted from the expected geometry, based on a 14-vertex polyhedron (Figure 7-11B), in that the distance from the lower framework carbon to the boron at the bottom of the cage, shown here as a dotted line, is elongated ˚ . This bond-lengthening is interpreted [240] as being necessary to provide relief to the high connectivities of to 2.559(2) A the atoms involved, and is a feature commonly found in large carboranes and fragments thereof. At this writing the only other characterized 11-vertex hypho-carboranes are the derivatives of the azacarborane CNB9H14, discussed in Chapter 12. The NMe4 þ salt of hypho-C2 B8 H15
is stable in air for prolonged periods at room temperature. Salts with NMe4 þ or PPh4 þ as the cation are converted to hypho-7,8-C2 B6 H13
in alkaline media, and the treatment of NMe4 þ C3 B8 H15
with dilute HCl yields arachno-6,9-C2B8H13-5-Me (Section 6.2); passing the PPh4 þ salt through a silica column effects a quantitative conversion to the arachno-5,10-C2B8H12-6-Me
anion [240]. The hypho7,8-C2 B6 H13
anion combines with [Cp*RhCl2]2 to generate a closo-11-vertex rhodacarborane, 1,2,3-Cp*Rh(C2B8H9-4Me) (Chapter 13) [240].

7.2.4 Nido-C4B7H11 7.2.4.1 Synthesis

Neutral nido-tetracarbaundecaboranes (Chapter 5, Table 5-7), which are isoelectronic analogues of C3 B8 H11
and C2 B8 H11 2
(tricarbollide and dicarbollide) ions, are known in three isomeric forms and can be prepared by different routes. The first example of this class [241] was obtained upon pyrolysis of closo-1,5-C2B3H5 at 400  C in a hot-cold reactor having a cold surface at 0  C, which afforded a product that was proposed to be 1,2,8,10-C4B7H11 but was later shown, by ab initio/IGLO/NMR calculations [242], to be 1,7,8,10-C4B7H11 (7-38).

7.2 11-Vertex open clusters H

B

H

CH2SMe2

H

B

B

B C

C B

B B

C

KOH/THF

H H

B B

B B

A

H

H

C B

B

B

− KOH

B B

B B

B

B

B

H H

H

C

H

H

C H

H

−

C

B

B hypho-C3B8H−15

B = BH

H

245

hypho-C2B6H−13

B FIGURE 7-11 (A) Synthesis of hypho-C3 B8 H15
. (B) Hypho-11-vertex cage based on closo-14-vertex polyhedron with 3 missing vertexes.

Reaction of the carbon-bridged carborane arachno--5,6,9-[m(6,9)-RCH]RC3B7H11 (6-15, Section 6.2) with NaH forms a C4 B7 H11
anion, which generates 7,8,9,10-C4B7H11 (7-39) on heating [243]. The third isomer, now assigned the structure 2,7,9,10-C4B7H11 (7-40) [242], has been isolated as a minor product from the reaction of arachno-6,7C2B7H13 with acetylene at 120  C, described earlier in Chapter 6, Figure 6-10) [243]. 10 9

C

B

8

C

5

11

B

B C

6

B

B 4 B

3 1

C

7-38

B

C C

C

7

C 2

B

B B

B

B

B

C C

B C

B B

B B

C B

B

B

7-39

7-40

The rules for carbon placement discussed in Chapter 2 predict that the most stable nido-C4B7H11 isomer is 7-39, the only possible arrangement in which all four carbons occupy low-coordinate vertexes. This prediction is borne out by theoretical studies, including DFT [244] and IGLO calculations of 11B NMR chemical shifts [242] which indicate that the order of stability in these three species is 7-39 > 7-38 > 7-40. More broadly, analysis of all nine possible isomers shows that the preference of carbon for low-coordinate sites is more important than the minimization of carbon-carbon bonding interactions [242]. By analogy to their isoelectronic and isolobal C3 B8 H11
and C2 B8 H11 2
counterparts, the nido-C4B7H11 cages are formal 6-electron donors and might be expected to face-bond to suitable transition metal acceptor fragments [for example, M(CO)3 where M is Cr, Mo, or W] to form stable Z5-coordinated MC4B7 complexes. However, at present none have been reported.

7.2.5 Arachno-C4B7H13 7.2.5.1 Synthesis Although methylene-bridged C3B7 cages, such as the previously described 6-12, 6-13, and 6-15 (Section 6.2), can be viewed as arachno 11-vertex systems, only one unambiguous example of an 11-vertex arachno-C4B7 carborane, in which all four carbon atoms are fully integrated into the skeletal framework, is currently known. The reaction of 6,7-C2B7H13

246

CHAPTER 7 Eleven-vertex carboranes

with acetylene in diethyl ether at 120  C affords, in addition to small amounts of other products [243,245], a 4% isolated yield of 7,8,9,11-H4C4B7H6-10-Me-m(7, 11)-CH2 (7-41) [246] that is formally an arachno-C4B7H13 derivative. Me C

7-41

CH2

C

B C

C B

B B

B

B B

It is possible to describe 7-41 as a pentacarbon carborane [246] if the sp3-hybridized bridging carbon is viewed as part of the electron-delocalized cluster. However, this seems something of a stretch and unnecessarily blurs the distinction between carboranes and the classical organoboranes. The same issue arises in other species that contain hydrocarbon bridging groups, as in the C3B7 cages mentioned above and their related derivatives (Table 5-7), and in certain metallacarboranes discussed in Chapter 13.

7.3 11-VERTEX CLOSO CLUSTERS 7.3.1 Closo-CB10H11
7.3.1.1 Synthesis

Parent 2-CB10 H11
is obtained as a minor product during the conversion of (Me3N)CB10H12 to 7-CB10 H13
by treatment with sodium or sodium hydride in refluxing THF, as described in Section 7.2 [6,7]. A more efficient route is the oxidation of the THF adduct Na3CB10H11(OC4H8)1.85 with iodine [5]: Na3 CB10 H11 ðOC4 H8 Þ1:85 þ I2 ! Naþ 2-CB10 H
10 þ 2NaI þ 1:85 C4 H8 O C-substituted derivatives of closo-2-CB10 H11
are synthetically accessible by several methods; for example, oxidation of nido-7-PhCB10 H12
with I2 in aqueous KOH produces 2-PhCB10 H10
[16,247]. Similarly, nido-7-(Me3N)CB10H12 can be oxidized to closo-2-(Me3N)CB10H10, and deprotonation of the iodo derivative 7-(Me3N)CB10H11-4-I followed by oxidation leads to the formation of closo-2-(Me3N)CB10H9-3-I [23]. An entirely different approach, oxidative cage closure, has been employed to generate closo-2[(Me3Si)2CH]CB10 H10
(7-42) from nido-7-[(Me3Si)2CH]CB10H11-9-SMe2, a compound obtained on reaction of B10H14 with silylacetylenes (Section 7.2) [15]. − H

(Me3Si)2CH

B C

H

B B

B B

B B

B B B

SMe2

(Me3Si)2CH Na, NaH, LiEt3BH, or Cp2Co C = CH B = BH

B C

B B

B B

B

B

B

7-42

B

B

A similar process is observed in the previously described reaction of nido-7-MeCB10H9-m(9,10)-CMeH
(7-5) with PdCl2(PPh3)2, whose main product is a B-PPh3 derivative of the starting compound (Section 7.2). Also isolated from this reaction is closo-2-MeCB10H9-3-CMeHPPh3 (7-43), whose formation from 7-5 involves both cage closure and conversion of the bridging carbon atom into an exo-polyhedral phosphinoethyl substituent [39].

7.3 11-Vertex closo clusters

247

Me H

− Me

C

H

Me

B

B B

B B

B B

7-5

C PdCl2(PPh3)2 C = CH B = BH

B

B

B C

B B B

B

B

7-43

B

B B

C

PPh3

Me

B

B

7.3.1.2 Structure

Crystallographic studies of the closo-2-CB10 H11
parent ion have not been reported, but experimental and theoretical investigations [248,249] indicate that the cluster is nonrigid and has some non-triangular faces, thereby deviating from the closo-polyhedral geometry expected for an 11-vertex cluster having 12 skeletal electron pairs (Chapter 2). Indeed, the fact that the 11B NMR spectrum exhibits only three signals (instead of the expected seven) is evidence that the cage is fluxional in solution [250]. In this respect, the molecule resembles its isoelectronic closo-borane analogue B11 H11 2
, whose fluxionality is such that its low-temperature 11B NMR spectrum consists of a single peak [251,252]. Several crystal structures of closo-2-CB10 H11
C- and B-substituted derivatives are available (Table 7-6), all of which show the expected deltahedral cage structure shown in Figure 1-1 and are analogous to that of B11 H11 2
[253], with the cage carbon atom occupying one of the two available low-coordinate vertexes. No other isomer of CB10 H11
has been characterized, in accordance with theoretical calculations that show significantly higher energies for other cage geometries [254].

Table 7-6 Closo-2-CB10H11
Derivatives Compound Synthesis and Characterization 2-CB10 H11
(Li, Na, K, Rb, Cs salts) 2-CB10 H11
2-PhCB10 H10
2-(Me3Si)2CH-2-CB10 H10
2-(Me3Si)2CH-2-CB10H9-6-SMe2 2-(Me3Si)2CH-2-CB10H8-4-OH-6-SMe2 2-Me3N-CB10H10 2-Me3N-CB10H9-3-I 2-MeCB10H9-3-CMeHPPh3 M[porphyrin-CH(OH)](CB10H11)
(M ¼ Co, Cu, 2H) Detailed NMR Studies 2-CB10 H11


Information

References

S, S IR S, S, S, S, S, S, S, S,

[558] [5,559] [248] [16,247] [15] [15] [15] [23] [23] [39] [422]

B

IR, UV

X, H, B, C X, H, B, IR X, H, B, IR X, H, B, IR H, B H, B X, H, B, P, MS H, cytotoxicity

[250,560] Continued

248

CHAPTER 7 Eleven-vertex carboranes

Table 7-6 Closo-2-CB10H11
Derivatives—Cont’d Compound Other Experimental Studies 2-CB10 H11


2-CB10 H11
(Li, Na, K, Rb, Cs salts) (Me3N)CB10H10(CO) (Me3N)CB10H10 (Me3N)CB10H10 (Me2PrN)CB10H10 MðenÞ3 2þ CB11 H12
]2 (M ¼ Co, Ni)

References

E IR, H IR, Raman UV Thermogravimetric analysis Solubility, thermolysis IR, UV

[250] [5] [249] [6] [561] [558] [6] [6] [5] [5] [562]

IR, H, B IR, H IR, MAG, UV, thermal decomposition

Theoretical Studies Molecular and electronic structure calculations CB10 H11
CB10 H11
(all isomers) 2-CB10 H11
2-Me3N-CB10H10 2-Me3N-CB10H9-3-I NMR calculations CB10 H11
1

Information

11

Vibrational analysis; electron density distribution; NOT closo ab initio DFT; nonrigidity Heat of formation, charge distribution Heat of formation, charge distribution

[248]

B

[560] 13

S, synthesis; X, X-ray diffraction; H, H NMR; B, B NMR; C, C NMR; P, UV-visible data; E, electrochemical data; MAG, magnetic susceptibility.

[254] [249] [23] [23]

31

P NMR; IR, infrared data; MS, mass spectroscopic data; UV,

7.3.2 Closo-C2B9H11 7.3.2.1 Synthesis The 11-vertex closo-carborane 2,3-C2B9H11, the only known isomer, can be obtained by dehydrogenation of nidoC2B9H13 at 100  C or by the reaction of nido-7,8- or 7,9-C2 B9 H12
with polyphosphoric acid at 70  C; nidoRR0 C2B9H11 carboranes undergo analogous processes to give the corresponding C-substituted derivatives (Table 7-7) [116,225–227]. As mentioned in the preceding section, protonation of 7,9-RR0 C2 B9 H10
anions (R ¼ H, Me, Ph) with H2SO4 at ambient temperature affords closo-2,3-RR0 C2B9H9 products (see Figure 7-3B) [118]. When conducted with nido-7,9-C2B9H11-n-X
ions (n ¼ 1 or 6; X ¼ Br or I), only the 2,3-C2B9H10-10-X product is obtained (Figure 7-12), a finding consistent with a single cage-closing mechanism in which a loss of the bridging proton is followed by the formation of bonds between B(8) and B(10) and B(11) [118]. Oxidative closure of 7,9-C2 B9 H12
to form 2,3-C2B9H11 can be accomplished using SnCl2 [255,256], and the carborane has also been obtained in 49% yield by decomposition of bis(dicarbollyl) nickel, Ni(C2B9H11)2 at 300  C [49]. The B-octamethyl species nido-7,8-H2C2B9H3Me8, mentioned earlier, is dehydrogenated on contact with silica gel in pentane solution and produces two isomers of closo-1,8-H2C2B9Me8 [92]. As described in Chapter 12, oxidation of the aluminacarborane 3,1,2-EtAl(Me2C2B9H9) by SnCl4 extracts the metal and forms the 11-vertex cluster 2,3Me2C2B9H9 [47].

7.3 11-Vertex closo clusters − 8

H

7

C

10

11 3

B

4

B

B B

2

6

−

B

9

B

C B

H+

B B

5

B

B 1B

X

B B = BH C = CH X = Cl, I

7,9-C2B9H11-1-X−

B

H+

B B

H

B

C

C

B

B

C

249

C B

B B

B B

B

B B

X

X 2,3-C2B9H10-10-X

7,9-C2B9H11-6-X−

FIGURE 7-12 Formation of 2,3-C2B9H10-10-X (X ¼ Br, I) via protonation and cage closure of nido-7,9-C2B9H11-1-X
and -6-X
anions.

Table 7-7 Closo-C2B9H11 Derivatives Compounds Synthesis and Characterization Single-Cage Derivatives No substituents on boron 2,3-C2B9H11

2,3-MeC2B9H10 2,3-Me2C2B9H9

2,3-Me4C2B9H7 2,3-Me2C2B9H9 PPh3 2,3-Me2C2B9H9 NEt3 2,3-Me2C2B9H9OH

Information

References

S, H, B, C S[thermal decomp of Ni(C2B9H11)2] S, B(“correct”), IR S, H, B, IR, R, MS S, B, IR, MS S, B B, R(Lewis bases) IR, Raman ED Dipole moment S, H, B, IR, MS, R S, B S, H, B, C S, H, B, IR, MS, R S, B, IR, MS S, B X S, E S, B, IR, MS S S S

[118] [49] [255] [116] [227] [226] [18] [249] [120] [563] [116] [226] [47] [116] [227] [226] [257] [265] [227] [116] [116] [116] Continued

250

CHAPTER 7 Eleven-vertex carboranes

Table 7-7 Closo-C2B9H11 Derivatives—Cont’d Compounds

Information

References

2,3-Me2C2B9H9 EtNC 2,3-R2C2B9H9 (R ¼ Me, Ph) 2,3-MePhC2B9H9 2,3-PhC2B9H10

S S, S, S, S, S, S S S S S, S,

[116] [118] [118] [18] [226] [116,225] [116] [116] [116] [116] [116] [118]

2,3-PhC2B9H10 PPh3 2,3-PhC2B9H10 NEt3 2,3-PhC2B9H10 OH 2,3-PhC2B9H10 EtNC 2,3-(p-BrC6H4)C2B9H10 2,3-(FC6H4)2C2B9H9 Hydrocarbon substituents on boron 2,3-C2B9H10-n-Me (n ¼ 1, 4, 8) 2,3-H2C2B9Me9 O- or S-containing substituents on boron 2,3-C2B9H7-4,7-(OH)2 2,3-C2B9H7-4,7-(OD)2 2,3-C2B9H6Br-4,7-(OH)2 2,3-C2B9H6Br-4,7-(OD)2 2,3-Me2C2B9H8-4-OMe 2,3-Me2C2B9H8-4-OH 2,3-Me2C2B9H7-4,7-(OH)2 2,3-Me2C2B9H7-4,7-OC6H4O 2,3-Me2C2B9H7-4,7-(OH)2 2,3-Me2C2B9H7-O2C6H4 2,3-Me2C2B9H7-O2C4H8 2,3-Me2C2B9H7-4,7-O-(CHMe)2-O 2,3-Me2C2B9H7-4,7-O-C6H4-O 2,3-Me2C2B9H7-4,7-O-C6H3Cl-O 2,3-Me2C2B9H7-4,7-O-C2H4-O 2,3-Me2C2B9H7-4,7-OC2H4O 2,3-Me2C2B9H7-4,7-(MeCHO)2CH2 2,3-Me2C2B9H6-10-Br-4,7-(OH)2 F-, Cl-, Br-, or I-containing substituents on boron 2,3-(FC6H4)2C2B9H8-4-F 2,3-C2B9H10-10-Cl

H, B, C H, B, C B, R(Lewis bases) B H, B, IR, MS, R

H, B, IR, MS*, R H, B, C

S, H, B, C S, H,B,C

[118] [92]

S, H, B, IR, MS,R S, H, B, IR, MS,R S, H, B, IR, MS,R S, H, B, IR, MS,R S (from 1,7-Me2C2B10H10), H, B, IR S, E S, H, B, MS, IR,R S, E S, E S, E S, H, B, MS S, H, B, MS S, H, B, MS S, H, B, MS S, H, B, MS S, H, B, MS S, E S, E S, H, B, MS X

[263] [263] [263] [263] [256] [265] [266] [265] [265] [265] [263] [263] [264] [264] [264] [264] [265] [265] [263] [258]

S, H, B, C S, H, B, C

[118] [118] Continued

7.3 11-Vertex closo clusters

251

Table 7-7 Closo-C2B9H11 Derivatives—Cont’d Compounds

Information

References

Multi-Cage Derivatives (2,3-C2B9H10)2 O(2,3-Me2C2B9H8)2 (2,3-Me2C2B9H7-O-)2 2,3-C2B9H10-4-(1-1,10-C2B8H9) 2,3-R2C2B9H8-4-(1,2-C2B10H10R0 ) (R ¼ H, Me; R0 ¼ H, Me)

S, S, S, S, S,

[227] [266] [263] [115] [115]

B, IR, MS H, B, C, MS H, B, IR, MS,R H, B, IR, MS H, B, IR, MS

Detailed NMR Studies 2,3-C2B9H11 2,3-C2B9H11 2,3-C2B9H11 2,3-C2B9H11 2,3-Me2C2B9H9 2,3-EtRC2B9H9 R ¼ Me, Et 2,3-PhC2B9H10 2,3-Ph2C2B9H9 2,3-(FC6H4)C2B9H10 2,3-(m/p-FC6H4)C2B9H10 2,3-Me2C2B9H7-4,7-(OH)2 2,3-Me2C2B9H7-4,7-OC2H4O 2,3-Me2C2B9H7-4,7-OC6H4O 2,3-Me2C2B9H6-10-Br-4,7-(OH)2 2,3-Me2C2B9H3D4-4,7-OC6H4O

H(2d), B(2d) H B C B B C B F(electronic properties) F(electronic properties) B, MS B, MS B, MS B B, MS

[564] [565] [566] [140,328] [566] [566] [328] [566] [261] [260] [566] [566] [566] [566] [566]

Other Experimental Studies 2,3-C2B9H11 2,3-Me2C2B9H7-4,7-(OH)2 2,3-R2C2B9H9 (R ¼ H, Me

Reaction with Me2S Condensation with glycols Metal insertion

[49] [264] [262]

ab initio Hþ charge Localized orbitals Isomer stabilities DFT; nonrigidity ab initio Geometry Geometry MNDO, extended Hu¨ckel, inner-shell electron energy loss spectra

[120] [565] [567] [568] [249] [254,569] [118] [118] [570]

Theoretical studies Molecular and electronic structure calculations 2,3-C2B9H11

C2B9H11 isomers 2,3-Me2C2B9H6-10-Br-4,7-(OH)2 2,3-C2B9H10-n-X (X ¼ F, Cl, Me; n¼ 1, 4, 8, 0) 2,8-C2B9H11

Continued

252

CHAPTER 7 Eleven-vertex carboranes

Table 7-7 Closo-C2B9H11 Derivatives—Cont’d Compounds Isomerization calculations 2,9-C2B9H11 C2B9H11 isomers

NMR calculations 2,3-C2B9H11

2,3-R2C2B9H9 (R ¼ Me, Ph) 2,3-MePhC2B9H9 2,3-C2B9H10-10-Cl 2,3-C2B9H10-n-Me (n ¼ 1, 4, 8) 2,3-(FC6H4)2C2B9H8-4-F 2,3-(FC6H4)2C2B9H9 2,3-C2B9H7-4,7-(OH)2

Information

References

Isomerization Cage rearrangement SCF isomerization Cage rearrangement mechanism Cage rearrangement

[571] [544] [259] [572] [573]

B–H coupling 11 B NMR IGLO GIAO; NMR þ GIAO; NMR þ GIAO; NMR þ GIAO; NMR þ GIAO; NMR þ GIAO; NMR þ GIAO; NMR þ 11 B NMR

[574] [560] [140] [118] [118] [118] [118] [118] [118] [118] [560]

geometry geometry geometry geometry geometry geometry geometry

S, synthesis; X, X-ray diffraction; H, 1H NMR; B, 11B NMR; C, 13C NMR; F, 19F NMR; 2d, two-dimensional (COSY) NMR; IR, infrared data; MS, mass spectroscopic data; UV, UV-visible data; E, electrochemical data; ED, electron diffraction.

7.3.2.2 Structure The C2v polyhedral geometry shown in Figure 1-1, with both carbons occupying low-coordinate vertexes adjacent to the unique B(1) (the only 7-coordinate boron in the C2Bn-2Hn family), was originally deduced from NMR spectra [18,116] and was later confirmed by an X-ray crystallographic analysis of the C,C0 -dimethyl derivative [257]. Detailed 11B, 13C, and 1H NMR studies have also been published (Table 7-7). No X-ray investigation of the parent carborane has been reported, but a gas-phase electron diffraction study of this compound supports the C2v structure [120]. An X-ray diffraction analysis [258] of 2,3-Me2C2B9H6-10-Br-4,7-(OH)2 (7-44) revealed a cluster geometry that is distorted from the “normal” closed polyhedron due to stretching of the B(1)-B(4) and B(1)-B(7) distances and is intermediate between the closo and nido structures. The partial cage-opening is attributed to the donation of electron density from the hydroxyl group lone pairs to the cage skeleton [258], consistent with earlier assumptions that Lewis base-C2B9 adducts have an open cluster geometry [116]. 1

Me

B

3

C

6

B

B

7-44

2

C

5 4B

8B

HO

B7 B11

B9

B 10

OH

Br

Me

7.3 11-Vertex closo clusters

253

7.3.2.3 Cage isomerization The 11B NMR spectrum of 2,3-C2B9H11 in solution exhibits the expected 1:4:2:2 pattern consistent with a non-fluxional cluster framework, in contrast to its monocarbon analogue CB10 H11
described earlier. No evidence for cage rearrangement has been seen experimentally, presumably because any higher-energy isomers that might form would quickly revert to the stable 2,3 system. However, a SCF theoretical investigation indicates that the energy barrier for interconversion is indeed low, and also predicts that the 2,9- and 2,8 isomers may be metastable and may be capable of stable existence [259].

7.3.2.4 Cage opening

As was noted in Section 7.2, conversion of 2,3-C2B9H11 to the nido-7,9-C2 B9 H12
anion can be accomplished via reaction with BH4
[115], while alkyllithium reagents [115] and dimethyl sulfide [49] afford nido-7,9-C2B9H11-9-L (L ¼ Me, n-C4H9) and nido-7,9-C2B9H11-10-SMe2 respectively. Other electron donors such as NEt3, PPh3, and OH
reversibly form nido-7,9-RR0 C2B9H9L adducts (R, R0 ¼ H, Me or Ph) [116,260]. In another example, interaction between 2,3C2B9H11 and its C-substituted derivatives, and C-lithiated closo-carboranes forms nido,closo linked-cage anions 7-45 and 7-46 [115]. R

R

R

B C

C B B

B

B

R

B B

Li

B C

+ B

B

B B

B B

B B

B

B Et2O

B

− R

B

B C

B

B

C B C

B

B

B

H

B B

B

B = BH R = H, Me R = H, Me

B B

C

C

B B

R

B

B

B B

7-45

R

H

C

C B B

B

B

B

C

B

H

B

C

B

+

B

Et2O

B B

B

B B C

B = BH R = H, Ph

−

B

B

B B

Li

B B

H

H

B C

B C

B B

B B

C

B

R

B B

B

B

H

B

B B

7-46

The electronic interaction between the cage and attached m- and p-fluorophenyl groups in 2,3-(FC6H4)C2B9H10 derivatives has been explored, and the carborane unit is found to be electron-accepting via an inductive mechanism [260,261]. Opening of the closo-C2B9 cluster is also observed with electron-rich d10 transition metals: reaction of 2,3Me2C2B9H11 with reagents such as Ni(1,5-C8H12)2, Pd(Me3C-NC)2, and Pt(PMe2Ph)3 in cold toluene yield 12-vertex icosahedral LnM(Me2C2B9H9) metallacarboranes (Chapter 13) [262].

7.3.2.5 Substitution at boron Treatment of 2,3-Me2C2B9H9 with chromic acid or other oxidants, when carried to completion, generates arachnoMe2C2B7H11 (Chapter 5) [116]. When conducted under air-free conditions at 0  C in benzene, this reaction affords the bis(hydroxy) derivative 2,3-Me2C2B9H7-4,7-(OH)2 (7-47) [263]; bromination of this compound with Br2 forms only the previously cited B(10)-Br derivative 7-44, whose structure has been crystallographically established [258]. Pyrolysis of 7-47 above 150  C gives a dimer that is linked by two oxygen atoms that bridge the B(4)-B(40 ) and B(7)-B(70 ) positions [263]. When 7-47 is heated with organic diols, cyclic condensation products (7-48) are obtained [263] via displacement of the OH groups, as shown by experiments with 18O-labeled glycols [264].

254

CHAPTER 7 Eleven-vertex carboranes

1

Me

B

3

C

6

5

B

7-47

4B

8B

HO

2

B11

C

B B7

B 10

B

Me

Me HO RHC

OH

C

C 4B

B9 OH

B

B

CHR 8B

O H

B

B B

R

7-48

O

B C

Me

C H R

One-electron electrolytic reduction of 7-48-type derivatives produces ESR-active radical anions in which the extra electron is associated with the carborane cage, while the addition of a second electron yields an unstable dianion [265]. The monohydroxyl compound 2,3-Me2C2B9H8-4-OH can be prepared by treatment of 2,3-Me2C2B9H9 with sodium periodate and 2M HCl in benzene. However, if conducted with acetic acid in benzene, the product is the 4,7-(OH)2 derivative; extended reaction times afford (Me2C2B9H8)2O, in which the two carborane units are linked by a single B2 2O2 2B bridge, as the only isolated product [266]. Other than the reaction with Br2 mentioned earlier, direct halogenation of closo-2,3-C2B9 carboranes has not been examined. B-halogenated derivatives can be prepared via cage closure of nido-C2B9H11-X
anions, as described above.

References [1] Grimes, R. N. Carboranes; Academic Press: New York, 1970. [2] Batsanov, A. S.; Fox, M. A.; Goeta, A. E.; Howard, J. A. K.; Hughes, A. K.; Malget, J. M. J. Chem. Soc. Dalton. Trans. 2002, 2624. [3] Burgos-Adorno, G.; Carroll, P. J.; Quintana, W. Inorg. Chem. 1996, 35, 2568. [4] Hernandez, D. M.; Huffman, J. C.; Todd, L. J. Inorg. Chem. 1987, 26, 213. [5] Hyatt, D. E.; Scholer, F. R.; Todd, L. J.; Warner, J. L. Inorg. Chem. 1967, 6, 2229. [6] Knoth, W. H. Inorg. Chem. 1971, 10, 598. [7] Knoth, W. H. J. Am. Chem. Soc. 1967, 89, 1274. [8] Knoth, W. H.; Little, J. L.; Lawrence, J. R.; Scholer, F. R.; Todd, L. J.; Warner, J. L. Inorg. Synth. 1968, 11, 33. [9] Bridges, A. N.; Gaines, D. F. Inorg. Chem. 1996, 34, 4523. [10] Hyatt, D. E.; Owen, D. A.; Todd, L. J. Inorg. Chem. 1966, 5, 1749. [11] Arterburn, J. B.; Wu, Ye; Quintana, W. Polyhedron 1996, 15, 4355. [12] Jelinek, T.; Plesˇek, J.; Hermanek, S.; Sˇtı´br, B. Collect. Czech. Chem. Commun. 1985, 50, 1376. [13] Jelinek, T.; Plesˇek, J.; Mares, F.; Hermanek, S.; Sˇtı´br, B. Polyhedron 1987, 6, 1981. [14] Scholer, F. R.; Todd, L. J. J. Organomet. Chem. 1968, 14, 261. [15] Ernest, R. L.; Quintana, W.; Rosen, R.; Carroll, P. J.; Sneddon, L. G. Organometallics 1987, 6, 80. [16] Franken, A.; Jelinek, T.; Taylor, R. G.; Ormsby, D. L.; Kilner, C. A.; Clegg, W.; et al. Dalton. Trans. 2006, 5753. [17] Jelinek, T.; Kilner, C. A.; Thornton-Pett, M.; Kennedy, J. D. Chem. Commun. 2001, 1790. [18] Berry, T. E.; Tebbe, F. N.; Hawthorne, M. F. Tetrahedron Lett. 1965, 715. [19] Romerosa, A. M. Thermochimica. Acta 1993, 217, 123. [20] Whitaker, C. R.; Romerosa, A.; Teixidor, F.; Rius, J. Acta Cryst. 1995, C51, 188. [21] Khan, S.-A.; Morris, J. H.; Siddiqui, S. J. Chem. Soc. Dalton. Trans. 1990, 2053. [22] Khan, S.-A. J. Chem. Soc. Pakistan 1997, 19, 103. [23] Morris, J. H.; Henderson, K. W.; Ol’shevskaya, V. A. J. Chem. Soc. Dalton. Trans. 1998, 1951. [24] Wilbur, D. S.; Hamlin, D. K.; Srivastava, R. R.; Chyan, M.-K. Nucl. Med. Biol. 2004, 31, 523. [25] Khan, S.-A. J. Chem. Soc. Pakistan 1991, 13, 38.

7.3 11-Vertex closo clusters [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60] [61] [62] [63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73]

255

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7.3 11-Vertex closo clusters [395] [396] [397] [398] [399] [400] [401] [402] [403] [404] [405] [406] [407] [408] [409] [410] [411] [412] [413] [414] [415] [416] [417] [418] [419] [420] [421] [422] [423] [424] [425] [426] [427] [428] [429] [430] [431] [432] [433] [434] [435] [436] [437] [438] [439] [440] [441]

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7.3 11-Vertex closo clusters [487] [488] [489] [490] [491] [492] [493] [494] [495] [496] [497] [498] [499] [500] [501] [502] [503] [504] [505] [506] [507] [508] [509] [510] [511] [512] [513] [514] [515] [516] [517] [518] [519] [520] [521] [522] [523] [524] [525] [526] [527] [528] [529] [530]

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