Icosahedral Carboranes

Chapter 9

Icosahedral Carboranes HERBERT BEALL

I. Introduction II. Structure and Bonding A. Structure B . Bonding C. Physical and Chemical Properties III. Synthesis A. Preparation of o-Carborane B . Thermal Rearrangement of o-Carborane C. Preparation of C B u H i 2 " IV. Metalation Reactions of the Icosahedral Carboranes . A. Alkali Metal and Magnesium Derivatives B. Zinc and Mercury Derivatives C. Transition Metal σ-Bonded Icosahedral Carboranes V. Halogenation of the C 2 B i 0 H i 2 Carboranes A. B-Halocarboranes B . C-Halocarboranes VI. Organic Chemistry of the C 2 B i 0 H i 2 Carboranes . . A. Alkyl and Aryl Derivatives B. Alcohol, Ether, Aldehyde, and Ketone Derivatives C. Carboxylic Acid and Ester Derivatives VII. Inorganic Chemistry of the C 2 B i 0 H i 2 Carboranes . . A. Group IV-B Derivatives (Si, Ge, Sn, Pb) B . Group V-B Derivatives (Ν, P, As, Sb, Bi) C. Group VI-B Derivatives (O, S) D. Inorganic Derivatives of C B n H i 2 * VIII. Carborane-Based Polymers A. Polymers Containing Organic Linkages B. Polymers Containing Inorganic Linkages I X . Icosahedral Cage Degradation A. Reactions of the C 2 B i 0 H i 2 Carboranes with Bases B. Dicarbollide Insertion Reactions References

.

.

.

.

. .

.

.

.

302 303 303 307 308 312 312 314 315 316 316 317 317 318 319 320 321 321 324 327 328 328 331 335 336 337 337 338 339 340 340 341

301

302

HERBERT BEALL

I. INTRODUCTION The icosahedral carboranes, 0-carborane [l,2-dicarba-c/ctf0-dodecaborane( 12)], w-carborane [ 1,7-dicarba-c/0S0-dodecaborane( 12)], and pcarborane [l,12-dicarba-c/0^0-dodecaborane(12)]* (Fig. 9.1), are a group unique among the boron hydrides in their ease of preparation in large quan­ tities and their great chemical stability under a wide variety of conditions.

oCartorane m-Carborane p-Carborane Fig. 9.1. The boron-carbon framework and accepted numbering system of 0-carborane, w-carborane, and /7-carborane. The boron atoms are indicated by the open circles and the carbon atoms by the filled circles (from reference 5b). These attributes have allowed investigators to study their properties in great detail and to considerable reward. Therefore, it is not surprising that the icosahedral carboranes are the first among the boron hydrides in having a promising commercial application, that of being constituents in hightemperature polymers. The high symmetry of the icosahedron provides geometric fascination and also is likely responsible for extensive electron derealization in these carboranes. The icosahedral carboranes have been termed "superaromatic" (7), and much theoretical and chemical effort has been spent to investigate the justification for this term. These carboranes have proved interesting to researchers in fields far re­ moved from boron hydrides. Thus a very extensive organic chemistry has been established for all three of the icosahedral carboranes, particularly, 0-carborane, and also many derivatives of nonmetals such as silicon, phos­ phorus, and sulfur, have been prepared. A number of derivatives with car­ borane units σ-bonded to both transition and nontransition metals have been made and π-bonded transition metal complexes are plentiful which have as ligands icosahedral carboranes with one or more boron atoms removed. The scope of the chemistry of the icosahedral carboranes is obviously vast. Icosahedral geometry is also observed in the monocarbon carborane * The trivial names 0-carborane, m-carborane, and p-carborane are convenient and in common use and are employed throughout this chapter. The names given in paren­ theses above are those proposed by the Nomenclature Committee of the Division of Inorganic Chemistry of the American Chemical Society. The two-number prefix to each of these names indicates the position of the carbon atoms in the boron-carbon icosa­ hedral cage.

9. ICOSAHEDRAL CARBORANES

303

1

anion, C B n H ^ " [dodecahydromonocarba-c/0.90-dodecaboronate(l —)]. The chemistry of this ion remains largely unexplored. Other boron hydride deriva­ tives having icosahedral geometry but having other atoms besides boron and carbon in the icosahedral skeleton are discussed in Chapter 11 and the 2 icosahedral ion B 1 2H 1 2 " is covered in Chapter 8.

II. STRUCTURE AND BONDING A. Structure X-ray crystal structure determinations of nine derivatives of 0-carborane (2) have established the near icosahedral geometry of the boron-carbon poly­ hedron with carbon atoms adjacent. Examples of 0-carborane derivatives for which crystal structures have been determined are given in Figs. 9.2 and 9.3 with the accepted numbering convention indicated. The shorter covalent radius of carbon with respect to boron is reflected in all cases in a slight distortion from a perfect icosahedron to a figure in which the C-C separation is shorter than that of B - C which is in turn shorter than that of B - B . Selected cage atom separations and average C - B and B - B distances are given in Table 9.1 for those 0-carborane derivatives for which the crystal structures have been determined. Four X-ray studies (5) have been performed on m-carborane derivatives and these studies confirm that the boron-carbon cage is generally icosa­ hedral and that the carbons are separated in the 1 and 7 positions. The struc­ ture of the dibrominated derivatives of m-carborane is shown in Fig. 9.4

Fig. 9.2. Molecular structure of dibromo-o-carborane. Cage boron atoms are open circles and cage carbon atoms are filled. The large filled circles represent bromine and the small open circles hydrogen (from reference 2d).

304

HERBERT BEALL

Fig. 9.3. Molecular reference 2/).

structure of C,C'-dimethyltetrabromo-0-carborane

(from

with the accepted numbering indicated. Selected cage atom separations and average C - B and B - B distances for the three w-carborane derivatives are given in Table 9.2, and it should be noted that the degree of distortion of the m-carborane cage is not a settled question. In dibromo-m-carborane (3b) and decachloro-m-carborane (3a), the average C - B distances are shorter than average C-C distances which is in general agreement with the results observed for 0-carborane. Thus in these two compounds the boron-carbon cage is not a regular icosahedron and, in particular, both of these structures feature a long separation between B 2 and B 3 of 1.89 A. It has been stated that this feature is probably indicative of the tendency of the C atoms to remove electrons preferentially from the vicinal Β atoms. However, in the

Fig. 9.4. Molecular structure of dibromo-m-carborane (from reference 3b).

1.64 1.70° 1.67 1.63 b 1.66 1.65

Cx-C2

1.68 1.73 1.77 1.66 1.74* 1.77

Ci-B3 1.70 1.72 1.75 1.73 b 1.68 1.75

Ci-B4 1.85 1.73 1.75 1.73

B4-B5

1.78 1.76 1.70 1.75 1.74 1.81

B3-B8

1.74

B3-B4

1.72 1.72 1.71 1.72 1.71 1.72

Αν. C-B 1.80 1.78 1.77 1.80 1.77 1.79

B4-B8 1.77 1.77 1.83 1.78 1.80 1.82

B4-B9

Av. ReferB9-Bi2 B-B

1.79 1.76 1.78 1.77

1.77

ence 1.81 1.78 1.81 1.78 1.77 2b 1.75 1.82 1.82 1.69 1.81 1.73 1.80 1.75 1.79 1.76 1.74 1.78

B8-B9

Structure is rotationally disordered and this separation is measured between a carbon atom and a hybrid atom which is postulated to be ib carbon and i boron. Rotational disorder is likely and atoms, 1, 2 and 6 may be f carbon and J boron.

a


Compound

Selected e-Carborane Cage Atom Separations, A

TABLE 9.1

9. I C O S A H E D R A L C A R B O R A N E S 305

2g 2d 2e 2f

2a

1.68 1.73

Ci-B4

Αν. C-B B2-B3

B4-B8

1.83 1.73

B4-B5

1.72 1.74

B3-B4

1.70 1.89 1.74 1.69 1.89 1.73 1.73 1.74

C1-B5 1.81 1.73

B4-B9

1.80 1.73

B5-B9

1.75 1.70 1.74

3a 1.77 1.74

Av. ReferB9-B10 B-B

In this structure the carbon atom not bearing the methyl substituent was not differentiated from the cage boron atoms.

1.64 α 1.73

w-B10Cli0C2H2 m-B10Br2H8C2H2 m-B10Br3H7C2(CH3)H

a

Ci-B2

Compound

Selected m-Carborane Cage Atom Separations, A

TABLE 9.2

1.78 1.73

ence

306 HERBERT B E A L L

3b 3c

307

9. ICOSAHEDRAL CARBORANES

C-methyl derivative of tribromo-m-carborane (3c) the icosahedron is essen­ tially perfectly regular although standard deviations of the individual cage atom separations were not given. In all of these structures determination of the precise location of boron and carbon atom positions is hampered by the presence of the halogen atoms and the question of the exact geometry of m-carborane awaits a really precise structural study. Electron diffraction studies (4) are in general agreement with the X-ray results for o- and m-carborane, although unique structures could not be determined. The structure of /?-carborane has been determined by electron diffraction (4a) which has shown that the main distortion from icosahedral geometry of the boron-carbon cage is that the diameter along the C . . . C axis is ~ 10% shorter than a diameter along a Β . . . Β axis, again reflecting the shorter covalent radius of carbon. General acceptance of the 1,12 icosa­ X 1 hedral structure for p-carborane resulted from the B nmr spectrum con­ sisting of one doublet which collapses to a singlet on decoupling (5). 2 That C B n H 1 2~ is icosahedral and thus isostructural (6) with B 1 2H 1 2 ~ n is supported by its B nmr spectrum (7). B. Bonding The icosahedral carboranes can be formally viewed as being the products of replacement of two B H " units by CH in the icosahedral borane ion 2 B i 2 H 1 2 " . Thus, the "extra" two electrons of the carbon atoms are probably delocalized in an extensive fashion, and owing to their greater electronega­ tivity the carbon atoms must withdraw significant electron density from their neighboring boron atoms. Hence in o- and m-carborane, the negative charge of the boron atoms will increase with decreasing number of carbon atoms which are nearest neighbors (8). In 0-carborane the relative charges of sym­ metry equivalent boron atoms should be: most negative, 9,12 and 8,10; intermediate, 4,5,7,11; least negative, 3,6. For m-carborane the order of decreasing negative charge should be: 9,10 > 5,12 # 4,6,8,11 > 2,3. For /j-carborane, the boron atoms must be identical and bear negative charge. TABLE

9.3

Calculated Framework Charges in 0-Carborane

Reference Atoms C(l,2) B(8,10) B(9,12) B(4,5,7,ll) B(3,6)

la

2d

9a

+ 0.29 -0.16 -0.16 -0.03 + 0.08

+ 0.29 -0.28 -0.24 -0.02 + 0.26

-0.29 -0.27 -0.02 + 0.22

—

308

HERBERT BEALL TABLE 9.4 Calculated Framework Charges in m-Carborane

Reference Atoms

la

9b

C(l,7) B(9,10) B(5,12) B(4,6,8,H) B(2,3)

+0.15 -0.16 -0.03 -0.03 + 0.10

-0.25 -0.06 -0.03 + 0.13

—

Lipscomb and co-workers have performed extensive molecular orbital calculations on the icosahedral carboranes including population analyses (1) for the cage atoms of the three neutral isomers which appeared prior to the publication of the discovery of these compounds. The cage charge distribu­ tions from these calculations and more recent and less empirical studies (2d,9) are given in Tables 9.3 to 9.5 and agreement with the general considerations given in the previous paragraph can be seen. Chemical evidence, particularly from electrophilic halogenations, supporting these calculations is discussed later in this chapter. TABLE 9.5 Calculated Framework Charges in a

/?-Carborane

Atoms

Changes

C(l,12) B(2-ll)

+ 0.15 -0.03

C. Physical and Chemical Properties Dipole moment measurements (10) of 0-carborane (4.31 D), 1,2-dibromo0-carborane (2.82 D), and 9,12-dibromo-0-carborane (7.21 D) support the hypothesis that the carbon atoms are at the positive end of the cage dipole. The dipole moment of m-carborane (10a, 10b, 11) is 2.78 D which correlates with the structure in which the carbons are separated more than in 0-carborane, and that of /7-carborane (11) is, as it must be, zero. All three of the icosahedral carboranes are stable white solids with odors similar to camphor. Their respective melting points, ο (294.5-295.5) (5a,12), m [272-273 (5a) or 263.5-265 (75)], and ρ [259-261 (5a)], are similar and reflect the decrease in polarity from o- to /?-carborane. Among the boron hydrides and related compounds they are remarkable for their thermal

309

9. ICOSAHEDRAL CARBORANES

stability and their resistance to acids, weaker bases, and air oxidation. All three undergo the same rather limited number of types o f reactions of which the most important are electrophilic substitution at the boron atoms using a Friedel-Crafts-type catalyst, photochemical substitution at the boron atoms, replacement of the acidic carbon hydrogens by the metals of certain active metallating agents like butyllithium, and removal o f the most positively charged boron atom in the cage by use of a very strong base. Significant differences, however, do exist in the chemistry of the three isomers. In par­ ticular, the adjacence of the carbon atoms in 0-carborane allows for the facile formation of five- and six-member exopolyhedral rings which are not possible in the meta and para isomers. This carbon atom adjacency also causes a greater positive charge to exist on the carbons of 0-carborane than on the carbons of the other two isomers. This results in a greater acidity of the carbon-bonded protons of 0-carborane than the equivalent protons in the other two compounds and a concomitant greater ease of 0-carborane

1•1 •

1000

Fig. 9.5.

1 • 1• 1. I • 1• 1 • 1 • 1• 1500

cps

1•1•

2000

1• 1 • 1 • I

2500

1 X

64.16 MHz B nmr spectrum of 0-carborane (from references 14 and 15b).

metalation. This effect is also evidenced by a greater electron-withdrawing power of 0-carborane with regard to C-bonded substituents. n Nuclear magnetic resonance spectroscopy, particularly B has been extensively applied to the icosahedral carboranes. The most highly resolved n B nmr spectra of the icosahedral carboranes (5b, 14) were taken at 64.16 MHz and are reproduced in Figs. 9.5-9.7 with chemical shifts relative to B(OCH 3) 3.

HERBERT BEALL

311

9. ICOSAHEDRAL CARBORANES

In 0-carborane (Fig. 9.5), there should be resonances from the four sym­ metrical groups of boron atoms (9,12), (8,10), (4,5,7,11), and (3,6). This is in agreement with the spectrum (Fig. 9.2) which shows four doublets with peak areas of 1.8 (low-field doublet) 2.0 and 6.2 (combined area of the two n highest-field doublets). The coupling constants between the B nucleus and the terminally bonded proton range from 148 to 177 Hz. In agreement with results on related boron hydrides, other coupling constants, including 1 1 1 1 1 1 1 0 B - B and B - B are very small. Experiments with o-carborane ^-substi­ n tuted halogen derivatives of known structure (75) have led to B resonance assignments for 0-carborane of (9,12) to lowest field and (8,10), (4,5,7,11), (3,6) to highest field. n The B nmr spectrum of m-carborane (Fig. 9.6) shows four doublet n resonances in accord with the structure of the molecule, and the B nmr spectrum of p-carborane (Fig. 9.7) shows the single expected doublet.

-18°

X

Fig. 9.8. Variable temperature H nmr spectrum of 0-carborane (60 MHz) (from reference 16).

The variable temperature Ή nmr spectra of o- and m-carborane have been 1 described (16). At temperatures above about — 90°C, the H nmr spectrum of 0-carborane (Fig. 9.8) shows a relatively sharp singlet due to the two C-H groups and four broad resonances due to the ten B - H groups. Since 1 1 1 n the various B - H coupling constants, as determined from the B nmr spectrum, are known to vary significantly (i.e., 148-177 Hz) (77) depending on the type of boron, the *H spectrum is deceptively simple owing to small

312

HERBERT BEALL TABLE 9.6 C - H Proton Chemical Shifts in Halogen Derivatives of the Icosahedral Carboranes

Compound 0-carborane 9-chloro-
(19)

S°(PPm) 3.50 3.40, 3.54 3.42, 3.53 3.67, 3.87 3.42 3.63 3.94 2.85 2.87 2.94 3.03 2.85 2.98 3.14 2.78, 3.19 3.07 2.68 2.79, 3.15 3.25

° Relative to tetramethylsilane.

chemical shifts between the different kinds of hydrogens. Upon lowering of the temperature, the observed spin-spin splitting pattern coalesced and the B-H resonance sharpened into a broad singlet of Lorentzian line shape with no separation of B - H *H nmr resonances. The collapse of the splitting X is attributed to quadrupole induced spin relaxation (18). The H nmr spec­ trum of w-carborane was observed to be more complicated than 0-carborane at high temperatures, indicating larger proton chemical shifts than 0-carborane. However, upon lowering the temperature, the spectrum collapsed in essentially the same fashion as in 0-carborane, giving a broad asymmetric singlet resonance at very low temperatures. X The H chemical shifts of the C-H protons of the icosahedral carboranes and some of their halogenated derivatives are listed in Table 9.6 (19).

III. SYNTHESIS A . Preparation o f o-Carborane

The most generally useful preparation of 0-carborane utilizes the reaction of acetylene and a solution of B10H12[(C2H5)2S]2 (20); the B 1 0H 1 2L 2 com-

313

9. ICOSAHEDRAL CARBORANES

plex is the reaction product of ( C 2H 5) 2S with decaborane(14) (21) [Eqs. (9.1) and (9.2)].* B10H14

+ ( C 2H 5) 2S

• B i 0H i 2 [ ( C 2 H 5) 2S ] 2

4-

H

(9·1)

2

HC—CH B1 H 0 1 [2 ( C 2 H 5) 2S ] 2 + H C = C H

•

\pj

+ 2 ( C 2H 5) 2S + H

2

(9.2)

BioHio

Other Lewis bases, particularly aliphatic nitriles and other dialkyl sulfides, have been substituted for ( C 2H 5) 2S in the 0-carborane preparation. It is not necessary to isolate the B 1 0H 1 2L 2 intermediate in these reactions and the acetylene is normally reacted with a solution containing the Lewis base and B 1 0H 1 4. It has been recently shown (22) that acetylene will react with B 1 0H 1 2L 2 (L = RCN) in the solid state to give pure 0-carborane which sublimes out of the reaction zone. This is a very useful small-scale preparation. The use of substituted reactants in the preparation of 0-carborane forms a very important preparative method to a huge range of substituted 0-carborane derivatives. In particular, substituted acetylenes have been used to prepare C-substituted 0-carboranes [Eq. (9.3)]. HC—CR B1 H 0 1 L 2 2 + HC=CR

•

\θ/

+ 2 L + H

(9.3)

2

B i 0 H 10

Representative R are alkyl and aryl (20a,23-30), alkenyl (20a,23,26,28-31), and alkynyl (29,30,32,33), although the dialkyne reaction will lead to at least some biscarborane [Eq. (9.4)]. HC—C—C—CH B1 H 0 1( 2C H 3 C N ) 2 + H C = C — C = C H

•

\θ/

\oj

B10H10 B10H10

HC—C—C=CH +

\oj B10H10

(9.4) In other reactions of substituted alkynes, R has represented ester (20a,28,30, 34-41), amine (20a,28), amide (28), acyl halide (37), halogen (20a), and ether (42-44) groups. The use of substituted B 1 0H 1 2L 2 compounds in the preparation of Bsubstituted 0-carboranes has been much less common, although ^-substi­ tuted halogen (45) and alkyl (20a) derivatives have been prepared in this manner. * The symbol £ ^H H

w

B10H10

is commonly used in the literature to represent σ-carborane and is useful particularly for depicting substitution reactions at carbon. HCB1 H 0 1 C 0 H

and

HCB1 H 0 1 C 0 H

are used to designate m-carborane and /7-carborane, respectively.

314

HERBERT BEALL

The reaction of boranes and acetylene has been shown to have general utility for producing c/ayo-carboranes (46). When B 1 0H 1 4 is used in this reaction, 0-carborane is produced in good yield providing another poten­ tially important preparative route to 0-carborane. B . Thermal Rearrangement of 0-Carborane

1. Preparation of m-Carborane and m-/p-Carborane Mixtures The practical routes to m-carborane (75) and also /?-carborane (5a) in­ volve thermal isomerization reactions which use 0-carborane as the starting material [Eq. (9.5)]. A 9 8 % conversion of 0-carborane to m-carborane can HC—CH (9.5) be realized using a flow system in which 0-carborane is held at 600°C during a residence time of less than one minute (47). I f the temperature of the sys­ tem is increased to 700°C, a mixture of isomers results containing 7 5 % m-carborane and 2 5 % /?-carborane (47,48) which can be separated on basic alumina. This procedure allows /?-carborane to be produced in reasonable quantities for the first time. The C,C'-dimethyl derivative of m-carborane has been produced (49a) in the reaction of B 2 H 6 with 1,6-(CH 3) 2-1,6-C 2B 8H 8 at 225°C. Recently, m-carborane has been prepared directly from m
2. Mechanism of Thermal Rearrangement Prior to the actual publication of an experimental information on the icosahedral carboranes, Lipscomb (50a) proposed a mechanism by which 0-carborane could be isomerized to m-carborane but not to /?-carborane via a cuboctahedral intermediate (Fig. 9.9).

Fig. 9.9. Rearrangement of o-carborane to m-carborane via a cuboctahedral inter­ mediate. This type of mechanism was later generalized (50b) to include a variety of polyhedral species having triangular faces in which certain pairs of adjacent triangular faces open into squares and then rejoin as triangular faces (Fig. 9.10).

9. ICOSAHEDRAL CARBORANES

315

Fig. 9.10. Movement of four polyhedron vertices in a rearrangement going by a diamond-square-diamond pathway.

Lipscomb terms this general family of mechanistic pathways as diamondsquare-diamond (dsd). Other proposed mechanisms for icosahedral carborane isomerizations include rotation of half of the icosahedron (75) in which case the intermediate geometry will be that of a bicapped pentagonal prism, and rotation of triangular faces of the icosahedron (57). Experimental information on these rearrangements has been gathered by observing the isomers that are formed when a monobromo o~ or w-carborane is heated to rearrangement tempera­ ture. I f 9-bromo-o-carborane is heated to 395°C, the appearance of all four possible monobromo-m-carborane isomers in a nonrandom mixture (52) rules out the mechanism with just the simple cuboctahedral intermediate which would lead only to 5-bromo-/w-carborane. In fact, the other three isomers of monobromo-0-carborane are seen as part of the isomerization mixture before conversion to 1007o meta products. It was claimed that no way was found to fit the quantitative aspects of these data with mechanisms involving rotation of half the icosahedron or any of its triangular faces. However, a good fit was obtained if the cuboctahedron mechanism was modified to allow rotation of triangular faces in the cuboctahedral inter­ mediate. This approach was extended to the higher-temperature isomerizations that yield /?-carborane, and again agreement with the data is only found for a mechanism in which triangle rotation occurs in a cuboctahedral intermedi­ ate (53). More work is warranted on icosahedral rearrangements to prove the exact mechanisms involved. Molecular orbital calculations (54) have shown that the relative stabilities of 0 - , m-, and /7-carborane should be reversed if these compounds are con­ verted to the respective dinegative anions and the reverse isomerizations have been verified by experiment (13,55). C. Preparation of C B n H 1 2~ The cesium salt of C B n H 1 2~ has been prepared (7) from C s C B 1 0H 13 by pyrolysis at 300°-320°C or reaction at 180°C with E t 3N B H 3. The prepara­ tion and properties of salts of C B n H i 3" are covered in Chapter 10 of this volume.

316

HERBERT BEALL

IV. METALATION REACTIONS OF THE ICOSAHEDRAL CARBORANES A. Alkali Metal and Magnesium Derivatives A large percentage of the well-studied reactions of the icosahedral car­ boranes and, in particular, those reactions which lead to the carboranebased polymers depend on metalation of one or both of the carborane cage carbons. The positive charge (2d) on these carbon atoms causes a mildly acidic hydrogen atom activity which allows a facile preparation of the oand m- but apparently not /j-carborane (56) Grignard reagents through reac­ tion with an alkyl magnesium halide (34,35) [Eq. (9.6)]. HC—CH yy

HC—CMgX + RMgx —

•

yy

BioHio

+ RH

(9.6)

BIQHIO

An interesting reaction occurs between magnesium and 1-chloromethyl0-carborane (57) [Eq. (9.7)], whereby the expected Grignard is probably H C — C C H 2C 1

C I M g C — C C H 3j

g M

\θ/

~eTheT*

(9.7)

^

B10H10

B20H10

formed followed by reaction with the acidic cage-bonded proton of another molecule. For synthetic purposes, more useful reagents are the mono- and dilithium derivatives of the three icosahedral carboranes which are easily prepared by reaction with «-butyllithium or phenyllithium (35,58) [Eq. (9.8)]. HC—CH

yy

LiC—CLi

+

2 LiR

yy

— •

B10H10

+

2RH

(9.8)

B10H10

The rate of reaction to form the carborane lithium compounds slows in proceeding from ortho to meta to para in line with the decrease in C-H hydrogen atom acidity (59). Preparation of monolithium derivatives of ortho- and meta- (and, perhaps, para-) carborane is complicated by an equilibrium that exists between the monolithium compound and the dilithium and unsubstituted compound in certain solvents (60) [Eq. (9.9)]. Fortunately, HC—CLi

2

\ θ / BioHio

HC—CH

LiC—CLi =

±

\ θ / BioHio

+

\ θ /

(9.9)

BIQHIO

this equilibrium seems to be shifted well to the left in benzene, and monosubstituted derivatives can be prepared in good yield using this solvent (28). Li, Na, K, and Ca derivatives of ortho-, meta-, and /?ara-carborane have been

317

9. ICOSAHEDRAL CARBORANES

prepared by reaction with the appropriate metal amide in liquid ammonia (28,34,35,55b,59c,61). The icosahedral carborane ion, C B n H 1 2" , reacts with w-butyllithium to form L i C B n H n " (7), a reagent of obvious value. B. Zinc and Mercury Derivatives A zinc derivative of 0-carborane, bis(l-phenyl-0-carborane) zinc, has been prepared from the reaction o f diethylzinc and l-phenyl-0-carborane at elevated temperature (62). Mercury derivatives of 0-, m-, and /?-carborane have been prepared by reaction of lithiocarboranes with mercury dihalides and alkyl halides (63-68) [Eqs. ( 9 . 1 0 ) and ( 9 . 1 1 ) ] . RC—C—Li

RC—C—Hg—C—CR

yy

yy

Β ι ο Η 10

RC—C—Li

(9.10)

B10H10

RC—C—HgCH 3 ™«+

\θ/

\o/

B10H10

\o/

B10H10

(9.11)

B10H10

C. Transition Metal σ-Bonded Icosahedral Carboranes A number of interesting compounds have been reported recently in which there is a σ bond from a metal atom to a carborane carbon. Lithiocarboranes have been reacted with (7r-C 5H 5)Fe(CO) 2I, Mn(CO) 5Br, and trans[(C 2H5) 3P]2PtCl2 to yield products presumed to have the structures shown below (69,70) [Eqs. (9.12) and (9.13)]: R—C—C—Fe(wC 5H 5)(CO) 2

RC—CLi \o/

<**w«*>tf >

B10H10

RC—CLi yy B10H10

yy

(9.12)

B10H10

RC—C—Pt^ [(caH5)3p]aptcia >

yy

CH 2 ^CH2 > ( C 2H 5) 2

(9.13)

B10H10

P(C 2H 5) 3 Some novel chelated complexes have been prepared from the C-C bonded dimer of 0-carborane (71). This dimer was reacted with butyllithium to form the dilithium derivative which was in turn reacted with CuCl 2, NiBr 2, and CoCl 2. Nuclear magnetic resonance and I R data support a bischelated struc­ ture (I). A similar type o f reaction has been used to prepare nonchelated complexes of l-methyl-0-carborane and phenyl-m-carborane (72). These

318

HERBERT BEALL

/

1 0

ΗΗιο

V

C

ΜΛ

\

Η 10 Οίο

I are converted to the respective lithium derivatives and reacted with ( R 3P ) 2N i C l 2 (R = C 6H 5 or C 2H 5) to give compounds of the type (R; iP) 2Ni-Fc—CCH 3

w

_ BIQHIO

A σ-bonded gold carborane (75) complex has been prepared using ( C 6H 5) 3P AuCl [Eq. (9.14)]. Recently more new σ-bonded compounds have been reported (3 i,73 b,73 c). Li—C—CC eH 5 (c eH 5) 3PAuci +

yy

(C 6H 5)3PAu—C—CC eH 5 \θ/ + LiCl

BioHio

(9.14)

BioHio

The first carborane derivative containing a boron-transition metal σ bond, H C ( B 1 0H 9F e ( C O ) 2( 7 r - C 5H 5) ) C H , has been recently prepared from the reac­ tion of a 2?-acylchloride of m-carborane with N a F e ( C O ) 2( 7 r - C 5H 5) and sub­ sequent loss of carbon monoxide from the product of this reaction (74) [Eqs. (9.15) and (9.16)]. HC[B 1 0H 9COFe(CO) 2(7rC 5H 5)]CH

HC(B 1 0H 9COC1)CH + NaFe(CO) 2(7rC 5H 5)

(9.15) HC[B 1 0H 9COFe(CO) 2 ^ C 5H 5) ] C H

-co

HC[B 1 0H 9Fe(CO) 2(7rC 5H 5)]CH (9.16)

V. HALOGENATION O F T H E C 2 B 1 0H 1 2 CARBORANES The reactions which lead to halogenated derivatives of the icosahedral carboranes can be divided into several distinct classes. One class comprises the electrophilic chlorinations, brominations, and iodinations which for oand m-carborane proceed in a very stereospecific manner with initial substi­ tution of the boron farthest from the cage carbon atoms. Similar selective substitution is observed for photochemical chlorination and bromination, but fluorination with elemental fluorine appears to be less selective. Use of

9. ICOSAHEDRAL CARBORANES

319

halogen-substituted B 1 0H 1 2L 2 compounds in the preparation of o-carborane to form J9-substituted o-carboranes has been mentioned in Section ΙΙΙ,Α, and isomerization of ^-substituted 0-carboranes to form ^-substituted wcarboranes has been mentioned in Section III,B,2. The dicarbollide insertion reactions leading to halogen derivatives which are halogenated only on the boron closest to the carbons are discussed in Section Ι Χ , Β and in Chapter 11. C-Substituted carboranes are prepared from metalated carborane deriva­ tives.

A. 2?-Halocarboranes

1. Halogenation by Electrophilic Reagents In the electrophilic chlorination, bromination, and iodination of ocarborane (15,75-77) and its C-methyl derivatives, substitution has been shown by various methods but, particularly, single-crystal X-ray studies to occur first at the 9,12 positions and then on borons 8,10 (2d-2f,10,75b-75d,75f,78). [Molecular orbital calculations (2d,75h) actually place a slightly higher nega­ tive charge in the ground state on positions 8,10 but it has been pointed out (2d,75h) that the five highest filled and most polarizable molecular orbi­ tals place a higher negative charge on atoms 9,12 than on atoms 8,10.] Electrophilic halogenation of the carbons and those borons connected directly to them (3,6; 4,5,7,11) does not seem to occur. Electrophilic halogenation of w-carborane has been studied less thoroughly than that of 0-carborane but various studies have shown that, except for fluorination, initial and principal halogen substitution occurs at positions 9,10 (3b,10c,75a,75b,75e,75f,75h,75i,76,79,80), those borons having the highest calculated negative charge (2d,75h), and the only borons not adjacent to carbon. Electrophilic bromination of 1-methyl-w-carborane has been shown to yield 257 0 of the 4,9,10-tribromo and 7 3 % of the 9,10,12-tribomo derivatives (3c). In /7-carborane, all boron atoms are equivalent and so only one isomer of monohalo-/?-carborane is possible. The number of isomers observed in the more highly substituted derivatives will depend on the steric and elec­ tronic effects of the halogen atoms already present. Electrophilic bromination and iodination of p-carborane yields the mono- and dihalo compounds, but electrophilic chlorination proceeds to the tetrachloro derivative (48,59d,81). Numerous isomers of the polychloro derivatives are formed but gas chromato­ graphic evidence shows that the substitution is not entirely random and the initially substituted chlorine atoms exert a substituent effect (82). Fluorine has been found to attack ο-, m-, and ^-carborane in an essen­ tially nonselective manner yielding i?-decafluorocarboranes as the ultimate product with no C substitution (83).

320

HERBERT BEALL

2. Photochemical Reactions In contrast to the electrophilic chlorination, bromination, and iodination reactions of the icosahedral carboranes, photochemical chlorination proceeds easily to the 5-decachloro derivatives (48,75h,76,77,84). The sequence of substitution of 0-carborane is parallel to that of electrophilic halogenation proceeding from the most negative boron atoms to the most positive. Ulti­ mate substitution occurs at borons 3,6, those closest to the carbons (2c,2g, 76,77,84b,84d,85). The photochemical chlorination of m-carborane leads to two monochloro isomers (84a,86) and is thus less specific than the electrophilic reaction. The photochemical chlorination of /7-carborane appears to go in an almost ran­ dom manner (48). Both 0 - and m-carborane resist photochemical bromina­ tion yielding only monobromo derivatives in the absence of a catalyst (77,84a).

B . C-Halocarboranes Halogen substitution at the carbons of the icosahedral carboranes cannot be effected by direct reaction but can be achieved by reaction of the halogen with the lithio (56,87,88) or Grignard (34,35,87c,89) derivatives of the carborane [Eqs. (9.17) and (9.18)]. L i C B 1 0H 1 0C L i

a

* > X C B 1 0H 1 0C X

RC—CMgBr RC—CX \o/ -3s\o/ B10H10

(9.17)

(9.18)

B10H10

The electron-withdrawing character of the halogen substituents in the ^-substituted halocarbons renders the protons on carbon relatively acidic especially in U-decachloro-0-carborane which is comparable to a carboxylic acid (77,83,84b,84d,87a,90). Thus the formation of metal salts of the Bdecachloro derivative of 0-carborane should be especially easy and, in fact, it can be achieved by treatment with aqueous alkali. This salt can then be reacted with chlorine to form the perchloro derivative (77,84b). The same compound can be prepared by reaction of 2?-decachloro-0-carborane with ΛΓ-chlorosuccinimide (84d,87a) [Eq. (9.19)].

HC—CH

\°/

BioClio

2

H 2C - ^C

1

H 2C^

C1C—CC1

\

/

N—CI

—

+ 2 C 4H 40 2N H BioClio

(9.19)

321

9 . ICOSAHEDRAL CARBORANES

VI. ORGANIC CHEMISTRY OF THE C 2 B 1 0H 12 CARBORANES Organic derivatives of the icosahedral carboranes can be formed in four ways. The first is by use of an organically substituted acetylene or B 1 0H 1 2L 2 compound in the preparation of the 0-carborane. This general method has been used to produce ^-substituted alkyl 0-carboranes and a wide variety of C-substituted compounds as detailed in Section ΙΙΙ,Α. C-Substituted alcohols and carboxylic acids cannot be prepared by this method. Second, a huge number of C-substituted organic derivatives of 0 - , m-, and /?-carborane have been prepared using reactions involving various mono- and dimetalated derivatives of these carboranes. In these reactions the carborane lithium compounds have been by far the most widely used. Third, a few 5-substituted alkyl derivatives have been formed by electrophilic substitution using a Friedel-Crafts catalyst. Last, ^-substituted alkyl, aryl, and alkenyl deriva­ tives have been formed through insertion reactions at the boron atom closest to the carbon atoms in 0 - and m-carborane. These insertion reactions are discussed briefly in Section I X of this chapter and in much more detail in Chapter 1 1 . A. Alkyl and Aryl Derivatives

1. Preparation The direct preparation of C-substituted alkyl and aryl 0-carboranes is described in Section ΙΙΙ,Α. In addition, many examples are known for the metathesis reactions of primary alkyl bromides or iodides with metal deriva­ tives of 0-carboranes (24,35,76,91), w-carboranes (13,59c,61a,76,92), and /7-carboranes (92a) to give the appropriate C-substituted derivatives [Eq. (9.20)].

RC—CM

RC—CR'

yy

+

R'X —

•

yy

+

MX

(9.20)

B 1 0H i 0

B10H10

Similar reactions (60) are known for the carborane Grignard reagents, the preparations of which are described in Section IV,A [Eq. ( 9 . 2 1 ) ] . The GrigRC—CMgBr yy BIOHIO

RC—CR' +

R'Br

—

•

yy

+

Μ 8 Β Γ2

(9.2

ο

BIOHIO

nard reagent will also react with dialkyl sulfates, alkyl /7-toluenesulfonates, and benzyl halides (60). Alkyl chlorides react only very slowly with metal derivatives of the icosahedral carboranes (91c) and secondary and tertiary alkyl halides do not seem to react at all (91c). The substituted 0-carboranes which are obtained in these reactions can generally be isomerized in reason­ able yield to the respective m- and /?-carboranes (25,93).

322

HERBERT BEALL

The adjacency of the carbon atoms of 0-carborane allows for the forma­ tion of exocyclic ring derivatives using dimetalated 0-carborane or the 0-carborane di-Grignard reagents and the appropriate dibromide or diiodide (24,60,91c) [Eq. (9.22)]. The geometries of m- and /7-carborane do

CH 2Br

NaC—CNa

CH2 BioHio

CH 2Br

C H 2 + 2 NaBr

(9.22)

C—C

\°/

BIQHIO

not allow the formation of such cyclic compounds. A particularly interesting species is formed when the product of the reaction of dilithio-0-carborane and cw-l,4-dichloro-2-butene is dehydrogenated with 7V-bromosuccinimide (NBS) (94a) [Eq. (9.23)]. Proton nmr and ultraviolet spectra indicate aromatic

LiC—CLi \θ/ + BIQHIO

Η Η )c=c( C1CH2

C—C • \θ/

CH 2C1

BIQHIO

C—C • \θ/ BioHio

(9.23)

character for the carbon ring (94). The compound is thus a carborane analog of naphthalene containing two fused aromatic systems. See also reference (94b). C-Substituted alkenyl derivatives of 0-carborane have generally been prepared by the reaction of an alkenylacetylene with the B 1 0H i 2 L 2 com­ pound and these have not been successfully isomerized to the corresponding m-carborane derivatives. Some alkenyl derivatives of 0-carborane have also been prepared through reaction of Grignard reagents (34,35,60,90,91). Derivatives of 0- and m-carborane have also been prepared by pyrolysis of certain of their C-substituted ester derivatives (35,95) [Eq. (9.24)]. Ο II H C — C C H 2C H 2O C C H 3 yy B10H10

HC—CH=CH2 yy

+ C H 3C O O H

(9.24)

BIQHIO

Alkynyl 0-carboranes can be prepared from the reaction of dialkynes and B 1 0H 1 2L 2 compounds as discussed in Section ΙΗ,Α and by the reaction of alkynyl halides on metalated 0-carboranes (91c). No alkynyl derivatives of m- or /?-carborane have been reported.

323

9. ICOSAHEDRAL CARBORANES

2. Properties of C-Substituted Alkyl and Aryl Derivatives The alkyl derivatives of o- and m-carborane are generally stable crystal­ line solids which are unreactive to acids and bases (26,27). Haloalkyl ocarboranes having the halogen substituted on the α-carbon (that carbon directly adjacent to the carborane cage) are unreactive with nucleophilic reagents (34,35) and react only very slowly with magnesium (28,35,61b) to form Grignards which themselves are relatively unreactive. Thus, 1-chloromethyl-0-carborane will not undergo a Finkelstein reaction with Nal, whereas the jS-chloroethyl compound reacts normally (28) [Eq. (9.25)]. Since Η — C — C C H 2— C H 2C 1

\θ/ BioHio

a

+ Nal - ^ V

Η — C — C C H 2C H 2I

\θ/

+ NaCl

(9.25)

B1 H 0 i0

the carborane cage is normally considered to be an electron-withdrawing group, the attack by the nucleophile should be helped in the 1-halomethyl case. The fact that the opposite effect is observed indicates that the dominant consideration is steric and the reaction of the 1-halomethyl compound is impeded by the difficulty in forming the 5-coordinate S N2 intermediate with the bulky carborane group on the 5-coordinate carbon. Neither 1-chloromethyl- nor l-bromomethyl-o-carborane will react with benzene in the presence of aluminum chloride to effect a Friedel-Crafts substitution, and this can be rationalized in terms of the electron-withdraw­ ing effect of the carborane cage which should destabilize the cationic attack­ ing species. The sluggishness of formation of Grignard reagents from 1halomethyl-o-carborane and their subsequent low reactivity is difficult to rationalize but may again be the result of steric considerations. The aryl derivatives of o- and w-carborane have been studied principally with regard to the electronic interaction between ring and cage by means of competitive substitution reactions. Thus in l-phenyl-o-carborane, halogena­ tion in the presence of aluminum chloride occurs preferentially on the carborane cage indicative of the electron-withdrawing effect of the icosa­ hedral cage. In contrast, when l-phenyl-o-carborane is reacted with 1007o nitric acid or mixed nitric and sulfuric acids, nitration occurs on the phenyl group (mostly para) and not on the carborane cage (96). This is not simply a reflection of a rate differential for nitration of the ring and of the cage since, as will be discussed in Section VII,B, reaction of nitric acid with o-carborane yields ^-hydroxy- and 5-nitrato-o-carborane and not a nitro derivative analogous to that of benzene (97). Aryl w-carboranes also undergo nitration to yield nitrophenyl derivatives (96b,96c). The C-alkenyl derivatives of 0-carborane which have a double bonded carbon atom directly adjacent to the carborane cage are remarkable in their inertness to cationic species. Thus, 1-vinyl- and l-isopropenyl-o-carborane react far more slowly with bromine than would be expected for compounds

324

HERBERT BEALL

containing carbon-carbon double bonds (26,29,34,98) [Eq. (9.26)]. Here the slowness of the reaction can be attributed to the electron-withdrawing effect of the carborane cage which reduces the electron density at the double bond. The addition of aluminum chloride to the system does not effect the Br

I

yy

HC—CCU=CH2

+ΒΓ2

—• yy

H C — C C H — C H 2B r

B10H10

(9.26)

B10H10

bromination of the olefinic portion of the molecule but does, as might be expected, cause substitution on the carborane cage (98). The bromination rate of the double bond is greatly increased by ultraviolet light (99). Little work has been done on the alkynyl derivatives of the icosahedral carboranes, but it has been noted that treatment of l-ethyl-0-carborane with a Grignard reagent does not cause metalation of the carborane carbon but rather of the acetylenic group (33) [Eq. (9.27)]. H - C - C ^ C H

Η — C — C — C = C MgBr

yy

yy

B10H10

BIQHIO

.27)

B. Alcohol, Ether, Aldehyde, and Ketone Derivatives

/· Preparation Although o-carborane alcohols cannot be prepared from acetylenic alco­ hols and B 1 0H i 2 L 2 compounds, an acetylenic ester can be employed instead and the resulting 0-carborane ester can be hydrolyzed or transesterified (27,28,30,34,35,100) [Eq. (9.28)]. Ο

ο

II R — C — Ο — C H 2— C — C H

yy

H O — C H 2— C — C H

+ CH3OH

yy

B10H10

J

+ R—C—OCH3

B10H10

Alcohols of 0- and m-carborane may be prepared from a variety of reac­ tions of metalated carboranes or carborane Grignard reagents with ethylene oxide (34,35,44,91e) [Eq. (9.29)], R—C—C—Μ

H 2C — C H 2

R — C — C — C H 2— C H 2O H

w • \/ — w Ο

B10H10

with α-epoxides (101) [Eq. (9.30)], R—C—C—Μ

W

BIQHIO

+

H 2C — C H R '

V — Ο

(9.29)

BioHio R — C — C C H 2— C H R '

W

BIQHIO

AH

(9.30)

(9

325

9. ICOSAHEDRAL CARBORANES with aldehydes and ketones (34,35,44,9lb,9le,102)

[Eq. (9.31)], Η

I

Ο R—C—C—Μ

V

\θ/

R — C — C — C — R'

+ R'-C-H

>

\θ/

BioHio

(9.31)

\QH

BioHio

and reportedly with certain esters, particularly the ethyl, propyl, and isopropyl esters of aromatic acids (103). The reactions of other esters with lithium derivatives of 0-carborane produce ketones (103) [Eq. (9.32)].

o ο R—C—CLi yy

ll

|| +

R — C — C — C — C 2H 5

cAH5—c—0CH3

—

•

yy

B10H10

+ LIOCH3

(9.32)

B10H10

Other methods of preparation of o-carborane alcohols include reaction of Grignard reagents with 0-carborane ketones (104) [Eq. ( 9 . 3 3 ) ] Ο

OH

li

I

C EH 5 — C — C C H 2 — C C EH 5

C 6 H 5 — C — C — C H 2 C ( C EH 5 ) 2 H M 8 B r

yy

* »

c

>

B10H10

yy

# 3 3 )

B10H10

and reduction of 0-carborane acids (44) and ketones (37,104,105). Alcohol derivatives of w-carborane are formed by analogous methods (59c,61a,104,

106). Ether derivatives of 0-carborane are generally prepared by the reaction of acetylenic ethers and B 1 0H 1 2L 2 compounds. Cyclic ethers can be produced by the condensation of 0-carborane diols (34,35) [Eq. ( 9 . 3 4 ) ] . H2C^ H O C H 2C - C C H 2O H

\°l

\

/

^ C H

2

\ ~ C 140°C

(9.34)

\°l \

BioHio

/

BioHio

Cyclic esters can also be produced in other reactions including reaction of l-lithio-2-bromomethyl-0-carborane with ketones, presumably, by the following path (91e) [Eq. ( 9 . 3 5 ) ] . No preparations of ether derivatives of w-carborane have been described. O

BrCH 2—C—CLi

yy

BioHio

||

+ R—c—R'

NL

i

BrCH 2—C—C—CR'

w

BIQHIO

H

2

C

X

X

CRR'

Vc

7

V/

B i o H 10

(9.35)

J

326

HERBERT BEALL

Aldehyde derivatives of o-carboranes can be prepared by hydrogenation of 0-carborane acid chlorides over palladium (107) and ozonization of vinyl0-carboranes (108) [Eq. (9.36)]. These two methods have also been successRC—CCH=CH 2

w

RC—CCHO

RC— C— C H — C H 2

o3

\o/

B10H10

(9.36)

BIQHIO

BioHio

fully employed in the preparation of aldehyde derivatives of m-carborane (38,95,107). Another method of preparation is the acid hydrolysis of the product of reaction of acetylene aldehyde diacetates (38) with B 1 0H 1 4 [Eqs. (9.37) and (9.38)]. H C = C C H ( O C O C H 3) 2 + B 1 H 0 14

d

i1 n a

^ "

f

«

a

H — C — C C H ( O C O C H 3) 2 \

0/

+

BioHio

(9.37)

HC—CCHO

H — C — C C H ( O C O C H 3) 2

\o/

H 2 2

V/

(9.38)

BIQHIO

B10H10

Ketone derivatives of 0-carborane can be produced in a variety of methods. As mentioned above, many esters react with lithium derivatives of 0-carborane to produce ketones (103). Lithium derivatives and Grignard reagents of 0-carborane also react with acid chlorides and anhydrides to produce ketones (103b,105,109) [Eq. (9.39)]. Cyclic and dimeric ketones are obtained o R—C—CLi I, yy + RC—c—ci

Ο II R—C—C—C— R'

yy

B10H10

+ U C 1 (9.39)

B10H10

in the reactions of appropriate lithio-0-carboranes with difunctional acid chlorides (109,110) [Eqs. (9.40) and (9.41)]. B10H10

:—CLi 2 LiC—CLi

w

+ 2 ci—c—ci

yy

C

^

B10H10

C

X

0=C

C = 0 + 4 LiCl

(9.40)

\°/

B10H10

2 RC—CLi \

/

10/ B i o H 10

Ο

Ο Ο I

I II

+ CI—C—C—CI

R—C—C—C—

w

+ 2 LiCl

(9.41)

B10H10

Analogous methods have been used to prepare ketone derivatives of m-carborane (111).

327

9. ICOSAHEDRAL CARBORANES

2. Properties The reactions of the alcohol, ether, aldehyde, and ketone derivatives of o- and m-carborane are, basically, those expected for the particular func­ tional groups although modified in some cases by the effects of the electron withdrawing and rather bulky carborane cage. Thus, l-hydroxymethyl-0carborane does not react with 4 8 % hydrobromic acid in sulfuric acid or with sodium bromide in concentrated sulfuric acid (61b). This effect is, presumably, due to hindrance by the o-carborane cage in the formation of the S N2 intermediate. Steric hindrance may also account for the reluctance of the α-ketone of 0-carborane to form 2,4-dinitrophenylhydrozones (104). C. Carboxylic Acid and Ester Derivatives

1. Preparation The dicarboxylic acids of 0 - , m-, and /7-carborane can easily be prepared by the reaction of the dilithiocarborane with C 0 2 and subsequent acidifica­ tion (34,35,58,59d,61a,106,l 11,112). Effective modifications of this method have been made using various monolithio derivatives and carborane Grig­ nard reagents (28,34,39,58,61a,112a,113). Carboxylic acids containing methyl­ ene units between the icosahedral cage and the carboxyl group can be pre­ pared by other methods including a Grignard synthesis (102J 13b) [Eq. (9.42)], and reaction of sodium derivatives of 0 - and w-carborane with H—C—CCH 2Br

W

ΒιοΗ 10

HC—CCH 2MgBr

-Sr W BIOHIO

HC—CCH 2COOH

V/

<-> 9 42

B I 0H I 0

sodium haloacetates in liquid ammonia (114) [Eq. (9.43)]. RC—CNa

\θ/ Β10Η10

R—C—CCH 2COOH

+ BrCH 2COONa

• -i^U

(9.43) Β10Η10

Carboxylic acid derivatives of 0-carborane can be prepared from 0-carborane esters and acid chlorides which have been prepared directly from the appropriate acetylene and a B 1 0H 1 2L 2 compound. Oxidation of 0-carborane alcohols also leads to the carboxylic acids (24,28,34,35,37,44,101). Ester derivatives of 0-carborane can be produced directly as mentioned immediately above and amides can be either produced directly from an acetylene amide or prepared by combination of a carborane acid chloride with an amine or ammonia (34,35,40,41,61b,91b,l 15).

2. Properties The distinguishing properties of the carboxylic acid and related derivatives of the icosahedral carboranes again demonstrate the electron-withdrawing

328

HERBERT BEALL

effect of the carborane cage. Therefore the 0-carborane acids are relatively strong with a pKa of 2.48 for the monocarboxylic acid (116). HC—CCOOH

The electron-withdrawing tendency of m-carborane cage is not so great and the pK& of the corresponding m-carborane carboxylic acid is 3.20 (116). This is indicative of the greater and more localized positive charge on the 0-carborane carbons (93) which is a factor in the greater stability of mcarborane than 0-carborane. This trend is maintained in the /7-carborane , carboxylic acid which has a pK& of 3.64 (59d). The C,C -dicarboxylic acids of 0 - and m-carborane differ in that while the latter is readily esterified by alcohols in the presence of acid (13), the former is not.

VII. INORGANIC CHEMISTRY OF THE C 2 B 1 0H 12 CARBORANES The reactions of the metalated (particularly with lithium) icosahedral carboranes play an even more important role in the preparation o f the inorganic derivatives of these compounds than in the preparation of organic derivatives. Whereas a very large variety of acetylenes bearing organic substituents have been successfully reacted with B 1 0H 1 2L 2 compounds to form C- substituted 0-carboranes, this route has almost no importance in the preparation of C-substituted inorganic derivatives. A. Group IV-B Derivatives (Si, Ge, Sn, Pb) A wide variety of ο-, m-, and /?-carborane derivatives with a silicon atom bonded directly to a carbon atom in the carborane cage have been prepared through the reaction of alkylchlorosilanes with lithiocarboranes (34,35,67,117) [Eqs. (9.44)-(9.50)]. Hydrolysis o f the 0-carborane bissilylchloride derivatives gives cyclic siloxane compounds (117b) [Eq. (9.51)]. In the hydrolysis of corresponding meta derivatives, formation of a small ring is unfeasible and the hydroxysilyl compounds are formed instead (117c-e) [Eq. (9.52)]. LiC—CLi

R 3SiC—CSiR 3

(9.44) CI

LiC—CLi

CI

R 2Si—C—C—SiR a

(9.45)

329

9. ICOSAHEDRAL CARBORANES

R2 H 2C

LIC—CLI +

X

R 2S I ( C H 2C L ) 2

CH 2

(9.46)

v/

c—c

BioHio

BioHio

R

I

LiCBi 0H 1 0CLi + RSiCl 3 ι LICB

1 LI

1 H 0 1 C 0

Cl 2SiCBioHioCSiCl 2 .ι

+

R 3S I C L

+

yy

SID

1

(9.47) (9.48)

R 3SiCBioHioCSiR 3

RC—CLI 2

R

RC—C—j-SiCl 2

4

(9.49)

\°/

BioHio

B10H10

LIC—CH +

w

BioHio R R2 C I S I2C — C S I C L

H aO

B10H10

\°/ R2

I

I

(9.51)

Ο

R 2Si X

B10H10

R2

(9.50)

R 3SiCH 2C—CH

R 3S I C H 2C L

\°/^ S i R /

2

c B10H10 — c R2

H ao

1

(9.52)

I

ClSiCB 1 0H 1 0CSiCl — — > HOSiCB 1 0H 1 0CSiOH

Analogous reactions occur in the reaction of carborane bissilylchloride reactions with ammonia and amines (117b-e) [Eqs. (9.53) and (9.54)]. Cyclic R2

R

R2

w

CISIC—CSICL

-^5^

R 2Si

(9.53)

SiR2

B10H10

B i o H 10

R2

R2

I

I

ClSiCB 1 0H 1 0CSiCl

NH-1

-

R2

R2

I

I

H 2N S i C B 1 0H 1 0C S i N H 2

(9.54)

o-carborane derivatives can also be produced in the reaction of a bissilyl­ chloride with dilithio-0-carborane (117b) [Eq. (9.55)], and in a variety of other reactions (118). Other reactions which produce carborane-silicon compounds include reactions of chlorosilanes with hydroxymethyl-0-carboranes (119) [Eqs. (9.56) and (9.57)], reaction of dilithiocarboranes with alkylchlorosiloxanes

330

HERBERT BEALL BioHio

l°\

CISiC—CSiCl + LiC—CLi

W

\°/

BioHio

BioHio

H O C H 2 C — C C H 2O H

yy

• R2s/

Nc

-,

\ i R

c/

2

(9.55)

\0/ BioHio R 3S i O C H 2C — C C H 2O S i R 3

Mia

yy

BioHio

(9i56)

BioHio

Si H O C H 2C - C C H 2O H

H

2

C

BioH.o

c/ /

\ CH2

^

(9.57)

BioHio

(120) [Eq. (9.58)], reaction of carborane Grignard reagents with alkoxysilanes (119c) [Eq. (9.59)], and various reactions of silanes with alkene derivatives of carboranes (119b,119c,121), e.g., Eq. (9.60). LiC-CLi

:

H 3

J*

(

( C H 3) 2S i ^

^

+ CI—Si—O—Si—CI

W

W

j

B I OHH 10 B

G

I C

•

1

3HC

S i ( C/ H 3) 2

C—C

W

(9.58)

γ/

H

BioHio C H 3C — C C H 2M g B r

C H 3C — C C H 2S i R 3

yy

\o/ BioHio BioHio

BIQHIO

HC—CCH=CH2 H S I C I 3 4-

yy B10H10

(9.59)

H C — C C H 2C H 2S i C l 3 —

^

yy

(9.60)

B10H10

Germanium derivatives of 0-carborane have been prepared from the reac­ tion of dilithio-0-carborane with dimethyldichlorogermane and subsequent reactions of the product with water or ammonia (117e) [Eq. (9.61)]. Dilithio-m-carborane has been reacted with tetrachlorogermane to form the expected bis product (llle) [Eq. (9.62)], and with dichlorodimethylgermane to form a mixture of 2 0 % of the expected bis product and 807 o of a polymer containing an average of six carborane units [Eq. (9.63)]. The preparations of tin derivatives of 0-, m-, and /?-carborane are essen­ f tially analogous to those of germanium and silicon (66,67,111 e,122). How­ ever, the larger size of the tin atom relative to germanium and silicon makes

331

9. ICOSAHEDRAL CARBORANES

+ 2 ( C H 3) 2G e C l 2

^

CH 3

CH 3

LiC—CLi

Cl—Ge—C—C—GeCl

BioHio

V/

CH 3 Η Ν

(CH^Ge^ X

CH3

BioHio

(9.61)

HaO ^ G e ( C H 3) 2

Ο

C—C

( C H 3) 2G e X

X

^ G e ( C H 3) 2

C—C

BioHio

BioHio L i C B 1 0H i 0C L i + GeCl 4 CH 3 L i C B 1 0H 1 0C L i

(9.62)

C l 3G e C B 1 0H 1 0C G e C l 3 CH 3

CH 3

I

CH 3

( C H 3 ) aa G c C l

> ClGeCB 1 0H 1 0CGeCl + CIGe—f-CB 1 0H 1 0CGe CH 3

CH 3

CH 3

CH 3

(9.63) formation of adducts with three carborane groups per tin atom possible (67,123) [Eq. (9.64)]. C 6H 5C — C L i

C 6H 5C — C

yy + snd4 BioHio

W

C 6H 5C — C

W

SnCl 2 +

BioHio

BioHio.

SnCl

(9.64)

Some polymeric lead derivatives of m-carborane have been prepared from dilithio-w-carborane and dialkyldichloroplumbanes (122a,122b) [Eq. (9.65)]. R L i C B 1 0H 1 0C L i + R 2PbCl 2

- C B 1 0H 1 0C P b - | —

(9.65)

R

B . Group V-B Derivatives (Ν, P, As, Sb, Bi) The phosphorus, arsenic, and antimony derivatives of the icosahedral carboranes are most readily derived from reactions of the appropriate halide with C-metalated carboranes; all are C-substituted. The nitrogen derivatives are formed by a variety of reactions and include some ^-substituted com­ pounds. When o-carborane is treated with 100% nitric acid, the products are a 5-hydroxy- and a 5-nitrato-o-carborane (97) [Eq. (9.66)]. Thus, although the carborane cage can be considered aromatic and similar to benzene in many

332

HERBERT BEALL

ways, this result is in sharp contrast to benzene which forms nitro compounds on reaction with nitric acid. It seems likely that this reaction goes in at least two distinct steps, the first of which is oxidation to the 2?-hydroxy compound and the second is the reaction of this with additional nitric acid to form the 2?-nitrato derivative. The 5-nitrato compound can be reduced to the same

yy

HC—CH

yy + yy

HC—CH + HNO3

—

>

HC—CH

B10H9OH

B10H10

(9.66)

B10H9ONO2

^-hydroxy compound with tin and hydrochloric acid (97). The position of substitution has not been firmly established but there is evidence that it occurs at the 9 boron atom (97) which with boron 12 is farthest from the carbon atoms and the position of initial electrophilic halogenation. It has been reported that m-carborane is unreactive to 1007o nitric acid (97b). Nitroso derivatives of 0-carborane can be prepared from the low-tem­ perature reaction of nitrosylchloride with lithiocarboranes (96bJ24) [Eq. (9.67)]. RC—CLi

yy

RC—CNO

NOC^

BioHio

yy

(967)

BioHio

Cyano derivatives of 0-carborane have been prepared by the reaction of lithiocarboranes with cyanogen chloride (125) [Eq. (9.68)]. It is interesting to note that the halide and pseudohalide derivatives are formed in equal amounts (125). Reduction of the cyano derivative with lithium aluminum leads to the amine (20a,28) [Eq. (9.69)]. C-Substituted amino 0-carboranes can be prepared in a route involving preparation of the azide from the acid chloride and treatment with sulfuric acid to form the amine (39,126) [Eqs. (9.70) and (9.71)].

yy

RC—CLi + CICN

—•

yy + yy

RC—CCN

RC—CC1

BIQHIO

B10H10

RC—CCN

RC—CCH 2NH 2 yAiHi.

yy

(9.69)

yy

B10H10

B10H10

Ο

Ο

II

II

C eH 5C—CC—Cl

W

B10H10

ο

C EH 5 C — C — C N 3

\°/

B i 0H 10

(9.68)

B10H10

Jsau

C 6H 5—C—C—CN

\o/

(9.70)

B10H10 C 6H 5— C — C — N H 2

¥

BIQHIO

(9.71)

9. ICOSAHEDRAL CARBORANES

333

An amino derivative of 0-carborane having a C - B - N linkage has been formed from l-lithio-0-carborane and chlorobis(dimethylamino)borane (127) [Eq. (9.72)]. Chlorophosphines react with lithiocarboranes to form a variety of deriva­ tives (66,67,91aJ28) [Eqs. (9.73)-(9.75)]. HC—CLi HC—CB[N(CH 3) 2] 2 ^ + C1B[N(CH 3) 2] 2 • \θ/ (9-72) B10H10

B10H10

(C 6H 5) 2PC—CP(C eH 5) 2

LiC—CLi yy

+

—

( C 6H 5) 2P C I

(9.73)

yy

•

BioHio

B10H10

LiCBi 0H 1 0CLi + C 6H 5PC1 2

LiC—CLi yy

+ C 6H 5P C I 2

CI CI • CeHsPCBxoH^CPCeHs CI CI I I C 6H 5PC—CPC 6H 5 — • yy

B10H10

(9.74)

(9.75)

BioHio

Cyclic phosphorus derivatives of 0-carboranes are prepared by methods generally analogous to those of the cyclic silicon derivatives mentioned above (91a) [Eqs. (9.76) and (9.77)]. Η CI

I

CI

C 6H 5PC—CPC 6H 5

C 6H 5P ^ P C eH 5 7 C—c

w B10H10

(9.76)

w B i o H 10 B10H10

LiC—CLi

CI CI C 6H 5P C - C P C 6H 5 ι 1 C—C

\oj

Μ ° > C 6H 5P ^ > C 6H 5 vi C—C 0 C—C B l o H l

(9.77) V

>/

w

B i o H 10

B10H10

Reaction of phosphorus trichloride with dilithio-0-carborane yields a cyclic structure (91a) [Eq. (9.78)], whereas phosphorus trichloride reacts with B10H10

A LiC—CLi C—C ^0/ - ^ k , , CIP^ \ θ B10H10

C—C

\°/ B10H10

(9.78)

334

HERBERT BEALL

dilithio-m-carborane to yield the difunctional derivative and a polymer (128) [Eq. (9.79)]. The bisphosphino derivatives of o-carborane are effective bidentate chelating ligands and a number of transition metal complexes have been prepared (129) [Eqs. (9.80) and (9.81)]. L i C B 1 0H 1 0C L i

PCl3

rci I

CI2PCB10H10CPCI2 ~H

α ι I

(9.79)

CB10H10CP

J

Cl 2

η

I ( C EH S) 2P C — C P ( C EH 5) A

Ν 6 Ί ΗΑ

'

' ° ,

P ( C 6H 5) 2

( C EH 5) 2P '

w

C-C

\ ° / B10H10

(9.80)

BIQHIO Ο

c

( C EH 5) 2P C — C P ( C EH 5) 2

Fe(CO)8

c \ l /

ο

c

( C eH 5) 2P

P ( C 6H 5) 2 C—C

\ ° / B10H10

(9.81) BIQHIO

Haloarsines, stibines, and bismuthines react with lithiocarboranes in a fashion parallel to that of the halophosphines (130). The larger size of the arsenic and antimony atoms allows the preparation of tris-0-carborane species whereas this is not observed with phosphorus (67) [Eq. (9.82)]. RC—C

RC—CLi yy

+ MCla

B10H10

-M

(9.82) B10H10

Bisarsine derivatives of 0-carborane have also been employed as ligands in transition metal complexes (130) [Eqs. (9.83) and (9.84)]. Cl 2 .P
( C 6H 5) 2A s C — C A s ( C 6H 5) 2

yy

+ pdci2

(CeH 5) 2As

As(C 6H 5) 2

(9.83)

w

C—C

BIQHIO

B10H10 C>

( C H 3) 2A s C — C A s ( C H 3) 2 yy + NI(CO) 4 B10H10

c

Ο

c

Ni ( C H 3) 2A s ^ As(CH 3) 2 + CO N C—C B10H10

(9.84)

335

9. ICOSAHEDRAL CARBORANES C. Group VI-B Derivatives (O, S)

Reaction of lithio derivatives of 0- and m-carboranes with benzoylperoxide or oxygen gives C-hydroxycarboranes (757) [Eq. (9.85)]. These CH 3C—CLi \oj

CH 3C—COH + ( C 6H 5C O ) 20 2 - j — •

y>/

BioHio

+ 2 C 6H 5COOH

(9.85)

BioHio

compounds are acidic (pK& l-hydroxy-0-carborane = 5.25; pK& 1-hydroxym-carborane = 8.24) (757). All three icosahedral carboranes can be oxidized by K M n 0 4 in acetic acid to give TMiydroxycarboranes. All four possible isomers of 2?-hydroxyo-carboranes are formed (752). This author has, however, been unable to repeat this work. The precursor of all sulfur derivatives of the icosahedral carboranes is the metalated carborane, almost always the lithium derivative. Reaction of the lithiocarborane with elemental sulfur leads to the lithium salt of the mercaptocarborane and with an organic disulfide leads to the thioether (755) [Eqs. (9.86) and (9.87)]. LiC—CLi

yy

LiSC—CSLi

RSC—CSR

—yy

yy B 1 0H 1 0

B10H10

LiSC—CSLi

\°/

H 2o

RSSR

(9.86)

B10H10

HSC—CSH

\o/

B i o H 10

(9.87)

B i 0H

A sulfinic acid of 0-carborane can be formed in the reaction of a lithio­ carborane with sulfur dioxide and subsequent hydrolysis (754) [Eq. (9.88)]. C 6H 5C — C L i

yy

+ so — •

C 6H 5C — C — S 0 2H

2

B10H10

yy

(9.88)

B10H10

Mercapto-0-carboranes can be converted to their salts in aqueous alkali. Salts of mercapto-0-carboranes react with iodine to form disulfides and methyliodide to form thioethers (134) [Eqs. (9.89) and (9.90)]. RC—CSM

yy BioHio RC—CSM

RC—CSCH3

sm+

yy

(9.89)

B1 H 0 io R—C—C—S—S—C—C—R

\o/

yy

yy

BioHio

BioHio

BioHio

(9.90)

336

HERBERT BEALL

The bismercapto derivative of m-carborane has been chlorinated to form the bischlorosulfenyl derivative, the chlorine atoms of which can be substi­ tuted by a variety of nucleophilic reagents (755) [Eq. (9.91)]. C1SCB 1 H 0 1 CSC1 0 'ROH ROSCB1 H 0 1 C 0 SOR

NH 3

(9.91)

K.CN

H 2N S C B 1 H 0 1 C 0 SNH2

NCSCB1 H 0 1 C 0 SCN

Displacement of the mercaptan protons in l,2-bis(mercapto)-o-carborane allows for chelation of both metals (133,136) [Eqs. (9.92)-(9.94)]. HSC—CSH

/

K C H ^ c ,

) /3

[ ( C 6 H 5

B1 H 0 10

^ C

H 10

(9.92)

B1 H 0 10

(9.93)

|^;B

P K N C

I O

\ - -

^x—s

HSC—CSH

B1 H 0 1 O 0

s—

x

J

HSC—CSH

I Ο

Ni^

s—c

s

y

BioHio

\°/

S

NaSC—CSNa Na

^

CoCl 2

Β1 Η 0 1 Ο 0 x

BioHio

BioHio

c

I

Co^

s

7

J Ο

B1 H 0 10

s—c (9.94)

and nonmetals (136a,137) [Eqs. (9.95) and (9.96)]. CeH5

I

p ^

HSC—CSH

w

C eH BP C l 2)

S

S C—C

(9.95)

V/

BIQHIO

BIQHIO

HSC—CSH

C 1 3B : N C C H 3

BIQHIO

c—S^ Β 1 0Η 10 Ο I BCI

(9.96)

"^c—s

D. Inorganic Derivative of CBnHx The lithio derivative of C B n H 1 2" has been reacted with trimethylchlorosilane to give the silane derivative (7) [Eq. (9.97)]. LiCBnHii" + CH 3SiCl

• CHaSiCBnHn"

(9.97)

337

9. ICOSAHEDRAL CARBORANES

VIII. CARBORANE-BASED POLYMERS Polymers are readily obtained from the icosahedral carboranes, and cer­ tain classes of carborane polymers which have high thermal stability are of considerable interest. Much work has been done to prepare polymers in which 0 - , m-, and /7-carborane units are connected by organic or inorganic groups. A few polymers have also been prepared which have carborane units that are pendant to the actual organic or inorganic polymer chain. The chemistry involved in the preparation of all of these polymers is related to reactions described in Sections VI and VII. A. Polymers Containing Organic Linkages These polymers include polyesters, polyformals, polyurethanes, and polyamides which have carborane groups in the backbone of the polymer, and polymethacrylates and polyolefins which have 0-carborane groups pendant to the polymer chain. A number of carborane polyester polymers have been formed from 0-carborane diols and diacids reacting either with each other or with other diols and diacids (138). None of these polymers show unusual thermal stability. A polyformal polymer of 0-carborane has been formed in the reaction of bis(2-hydroxyethyl-l-0-carboranylmethyl ether with formaldehyde (138b,138c) [Eq. (9.98)]. Carborane polyamides H O C H 2C H 2C — C C H 2

Ο

W

+

HCHO

BioHio C H 2C H 2C — C C H 2O C H 2C — C C H 2C H 2O C H 2 0 4 —

>/

BioHio

(9.98)

BioHio

have been prepared by the condensation of aromatic diamines with the acid chlorides of l,2-bis(/?-carboxyphenyl)-0-carborane or the analogous mcarborane compound (139). Polymethacylate polymers have pendant 0-carborane groups have been formed in the polymerization of l-methacyloyloxymethyl-0-carborane or its methyl derivatives (138d9140) [Eq. (9.99)]. Polymers presumably having Η

Η CH2

I =c I

— C H 2— C -

c=o I

C=0

ο

I

(9.99)

ο

I CH

C H 2CBioHio -

I

w

C H 2C — C H

BioHio

338

HERBERT BEALL

pendant carborane groups have recently been prepared by radiolytically induced polymerization of alkenylcarboranes (141). B. Polymers Containing Inorganic Linkages By far the most promising of the carborane polymers are the siloxanelinked polymers of m-carborane (Dexsil) which have been developed by the Olin Mathieson Chemical Corporation and have outstanding thermal stability. Siloxane polymers have also been prepared with pendant carborane groups. Other inorganic polymers of carboranes have been synthesized having m- or /^-carborane groups linked by single atoms of silicon, germanium, tin, lead, phosphorus, sulfur, and mercury. C H 3 0 { C H 3 ) 2 S i C B l oH | 0C S i ( C H 3 ) 2 O C H 3

I CH3 Dexsil

I GH

3

I CH

3

200 Polymer

The Dexsil polymers* are produced by methylchloride elimination reac­ tions involving the bismethoxydimethylsilyl derivative of m-carborane and substituted chlorosilanes, substituted chlorosiloxanes, or the bischlorodimethylsilyl derivative of m-carborane depending on the number of siloxyl groups desired between carborane units. Ferric chloride is used as a catalyst in all condensation reactions (142) as shown in Reaction Scheme I. * The Dexsil 100 polymer has one oxygen atom between the carborane groups, the Dexsil 200 polymer has two, and so forth.

339

9. ICOSAHEDRAL CARBORANES

Dexsil 100 is crystalline but the higher Dexsils are mostly elastomeric. These elastomers have been subject to rigorous testing and made into a wide variety of products including gaskets, coatings, Ο rings and seals, which have shown good mechanical properties at temperatures up to and even above 500°C (142dJ42e,143). An unusual 0-earborane polymer containing P-N-P linkages has been prepared from the cyclic chlorophosphine derivative of o-carborane (91a) [Eq. (9.100)]. Hard, inflexible polymers of m- and /?-carborane containing single atom links have been prepared utilizing some of the kinds of reactions outlined in Section VII (117e,122b,142eJ44). Among these are [Eqs. (9.101)(9.104). (CeH^P

BioHio

Μ c c c, p /

/

C

Μ

\

C

N 3P \

BioHio

ο

BioHio

a

NaNa

PN3

( C eH 5) 2P

C—C BioHio BioHio

A = N P

C 6H 5

/

P _ N = P - /

w ^

Ο

C 6H 5

Ρ

(9.100)

I CeHs

BioHio CH3

L i C B 1 0H 1 0C L i + (CH 3) 2SiCl 2

- S i — C B 1 0H 1 0C - [ LC

H

(9.101)

3

CH3

LiCB 1 0H 1 0(!:Li + (CH 3) 2SnCl 2

—L Sn—(^BioHxoC-l-

(9.102)

LCH3

C1SCB 1 0H 1 0CSC1 + L i C B 1 0H 1 0C L i L i C B 1 0H 1 0C L i + H gC l 2

—|"SCBi0HioC-^—

(9.103)

-[-HgSBioHxoC^

(9.104)

IX. ICOSAHEDRAL CAGE DEGRADATION The extensive chemistry of the degradation and especially the reformation of the icosahedral carborane cage is covered in detail in Chapter 11. For the sake of completeness of this chapter, a few reactions will be mentioned here.

340

HERBERT BEALL

A. Reactions of the C 2 B 1 0H 1 2 Carboranes with Bases Reaction of 0- and m-carborane with strong bases, such as methoxide ion, yields a product in which the base has attacked and removed the most posi­ tive boron atom in the cage (145). This is B3 in 0-carborane and B2 in mcarborane, in each case the boron closest to the carbon atoms [Eq. (9.105)]. C 2H 1 H 0 12 +

CH3O- + CH3OH

•

C 2B 9H 1 "2 + B ( O C H 3) 3 + H 2

(9.105)

The boron-carbon framework of each of the C 2 B 9 H 1 2" ions is proposed to be simply an icosahedron with one vertex removed. The twelfth hydrogen atom is considered to be located at the open face where the boron atom was removed, but the exact bonding of this hydrogen atom is uncertain (146). Several different reducing agents can be used to remove this twelfth hydrogen from the 11-atom boron-carbon cages of the C 2 B 9 H 1 2~ ions (147) [Eq. (9.106)]. C 2B 9H 1 "2 4-

NaH

• Na

+

2

(9.106)

+ C 2B 9H n - + H 2

2

The C 2 B 9 H n " ions have been named dicarbollide ions by Hawthorne. The numbering system of the parent carboranes is retained for these ions with the number of the removed boron atom indicated in parenthesis. Thus, the di­ carbollide ion of 0-carborane is called (3)-l,2-dicarbollide. B. Dicarbollide Insertion Reactions The dicarbollide ions have been reacted with a large number of different compounds to give products in which the icosahedral cage has been reformed with the insertion of a new atom, either metal or nonmetal. Thus, 3-phenyl0-carborane is prepared from the reaction of phenylborondichloride and (3)-l,2-dicarbollide (148) [Eq. (9.107)]. HC—CH

2

( 3 ) - l , 2 - C 2B 9H n - + C 6H 5B C 1 2

•

\θ/

+

2 CI"

(9.107)

3 CeHsBioHg

The product of this reaction can be converted to its dicarbollide ion with B(6) removed, and subsequent treatment of this ion with phenylborondi­ chloride leads to the formation of 3,6-diphenyl-0-carborane. It has not proved possible to further degrade this compound, indicating that only B(3) and B(6) can be removed by base attack. In other insertion reactions, 3-halo-0-carborane and 2-halo-m-carborane have been prepared by reaction of boron trifluoride or boron tribromide with a dicarbollide ion (147) [Eq. (9.108)]. The reaction of vinyldichloroborane C 2 B 9H n

2

—• C 2 B I Q H H X

(9.108)

341

9. ICOSAHEDRAL CARBORANES

with the 0/'/Ao-dicarbollide ion gives 3-vinyl-0-carborane (108) [Eq. (9.109)]. HC—CH (9.109) B10H9C — CH 2 Η Ozonation of 3-vinyl-o-carborane yields the ^-substituted aldehyde, 3-formyl0-carborane, and the ^-substituted carboxylic acid, 3-carboxy-o-carborane

(108\ ACKNOWLEDGMENT The author is grateful to the Petroleum Research Fund administered by the American Chemical Society and to Public Health Service Research Grant No. CA12025-01 from the National Cancer Institute for support during the writing of this review.

REFERENCES 1. a). R. Hoffmann and W. N. Lipscomb, J . Chem. Phys. 36, 3489 (1962); b). W. N. Lipscomb, Proc. Nat. Acad. Sci. U.S. 47, 1791 (1961). 2. a). D. Voet and W. N. Lipscomb, Inorg. Chem. 3, 1679 (1964); b). L. H. Hall, A. Perloff, F. A. Mauer, and S. Block, / . Chem. Phys. 43, 3911 (1965); c). J . A. Potenza and W. N. Lipscomb, J . Amer. Chem. Soc. 86, 1874 (1964); d). J . A. Potenza and W. N. Lipscomb, Inorg. Chem. 5, 1471 (1966); e). J . A. Potenza and W. N. Lipscomb, ibid. p. 1478; f). J . A. Potenza and W. N. Lipscomb, ibid. p. 1483; g). J . A. Potenza and W. N. Lipscomb, ibid. 3, 1673 (1964); h). R. W. Rudolph, J . L. Pflug, C. M. Bock, and M . . Hodgson, ibid, 9, 2274 (1970); i). A. A. Sayler, H. Beall, and J . F. Sieckhaus, J . Amer. Chem. Soc. 95, 5790 (1973); j). V. Subrtova, 2nd Int. Meet. Boron Chem., Leeds, England, 1974, Abst. No. 51. 3. a). J . A. Potenza and W. N. Lipscomb, Proc. Nat. Acad. Sci. U.S. 56, 1917 (1966); b). H. Beall and W. N. Lipscomb, Inorg. Chem. 6, 874 (1967); c). I. S. Astakhova, Yu. T. Struchkov, V. I. Stanko, and N. S. Titova, Zh. Strukt. Khim. 10, 1063 (1969); d). H. Hart and W. N. Lipscomb, Inorg. Chem. 12, 2644 (1973). 4. a). R. K. Bohn and M. D. Bohn, Inorg. Chem. 10, 350 (1971); b). V. S. Mastryukov, L. V. Vilkov, A. F. Zhigach, and V. N. Siryatskaya, Zh. Strukt. Khim. 10, 136 (1969); c). L. V. Vilkov, V. S. Mastryukov, P. A. Akishin, and A. F. Zhigach, ibid. 6, 447 (1965). 5. a). S. Papetti and T. L. Heying, / . Amer. Chem. Soc. 86, 2295 (1964); b). G. D. Vickers, H. Agahigian, E. A. Pier, and H. A. Schroeder, Inorg. Chem. 5, 693 (1966). 6. W. N. Lipscomb, "Boron Hydrides." Benjamin, New York, 1963. 7. W. H. Knoth,/. Amer. Chem. Soc. 89, 1274 (1967). 8. F. P. Boer, J . A. Potenza, and W. N. Lipscomb, Inorg. Chem. 5, 1301 (1966). 9. a). M. D. Newton, F . P. Boer, and W. N. Lipscomb, J . Amer. Chem. Soc. 88, 2353 (1966); b). M. D. Newton and W. N. Lipscomb, results published in Beall and Lipscomb (3b). 10. a). A. I. Echeistova, Yu. K. Syrkin, V. I. Stanko, and A. I. Klimova, Zh. Strukt. Khim. 8, 933 (1967); b). R. Maruca, H. A. Schroeder, and A. W. Laubengayer, Inorg. Chem. 6, 572 (1967); c). V. I. Stanko, A. I. Echeistova, I. S. Astakhova, A. I. Klimova, Yu. T. Struchkov, and Yu. K. Syrkin, Zh. Strukt. Khim. 8, 928 (1967).

342

HERBERT BEALL

11. A. W. Laubengayer and W. R. Rysz, Inorg. Chem. 4, 1513 (1965). 12. L. I. Zakharkin, V. I. Stanko, V. A. Brattsev, Yu, A. Chapovskii, and Yu. T. Struckhov, Izv. Akad. Nauk SSSR, Ser. Khim. p. 2069 (1963). 13. D. Grafstein and J . Dvorak, Inorg. Chem. 2, 1228 (1963). 14. R. L. Pilling, F . N. Tebbe, and M. F . Hawthorne, Proc. Chem. Soc, London, p. 402 (1964). 15. J . A. Potenza, W. N. Lipscomb, G. D. Vickers, and H. A. Schroeder, / . Amer. Chem. Soc. 88, 628 (1966). 16. C. H. Bushweller, H. Beall, M. Grace, W. J . Dewkett, and H. S. Bilofsky, / . Amer. Chem. Soc. 93, 2145 (1971). 17. G. R. Eaton and W. N. Lipscomb, " N M R Studies of Boron Hydrides and Related Compounds." Benjamin, New York, 1969. 18. a). H. Beall, C. H. Bushweller, W. J . Dewkett, and M. Grace, J . Amer. Chem. Soc. 92, 3484 (1970); b). D. Marynick and T. Onak, J . Chem. Soc, A p. 1160 (1970). 19. V. I. Stanko, V. V. Khrapov, A. I. Klimova, and J . N. Shoolery, Zh. Strukt. Khim. 11, 542 (1970). 20. a). T. L. Heying, J . W. Ager, S. L. Clark, D. J . Mangold, H. L. Goldstein, M. Hillman, R. J . Polak, and J . W. Szymanski, Inorg. Chem. 2, 1089 (1963); b). Μ. M. Fein, J . Bobinski, N. Mayes, N. Schwartz, and M. S. Cohen, ibid. p. 1111. 21. R. Schaeffer, / . Amer. Chem. Soc. 79, 1006 (1957). 22. H. Beall, Inorg. Chem. 11, 637 (1972). 23. L. I. Zakharkin, A. A. Ponomarenko, and O. Yu. Okhlobystin, Izv. Akad. Nauk SSSR, Ser. Khim. p. 2210 (1964). 24. L. I. Zakharkin, Izv. Akad. Nauk SSSR, Ser. Khim. p. 1114 (1965). 25. L. I. Zakharkin, V. N. Kalinin, and I. P. Shepilov, Dokl. Akad. Nauk SSSR 174, 606 (1967). 26. V. I. Stanko, V. V. Kopylov, and A. I. Klimova, Zh. Obshch. Khim. 35,1433 (1965). 27. L. I. Zakharkin, V. A. Brattsev, and V. I. Stanko, Zh. Obshch. Khim. 36, 886 (1966). 28. L. I. Zakharkin, V. I. Stanko, V. A. Brattsev, Yu. A. Chapovskii, A. I. Klimova, O. Yu. Okhlobystin, and A. A. Ponomarenko, Dokl. Akad. Nauk SSSR 155, 1119 (1964). 29. Μ. M. Fein, J . Bobinski, N. Mayes, N. Schwartz, and M. S. Cohen, Inorg. Chem. 2, 1111 (1963). 30. Μ. M. Fein, D. Grafstein, J . E. Paustian, J . Bobinski, Β . M. Lichstein, N. Mayes, N. Schwartz, and M. S. Cohen, Inorg. Chem. 2, 1115 (1963). 31. Μ. M. Fein and J . E. Paustian, Ind. Eng. Chem., Process Des. Develop. 4, 129 (1965). 32. J . A. Dupont and M. F. Hawthorne, J . Amer. Chem. Soc. 86, 1643 (1964). 33. J . A. Dupont and M. F. Hawthorne, U.S. Patent 3,254,117 (1966). 34. D. Grafstein, J . Bobinski, J . Dvorak, H. D. Smith, N. Schwartz, M. S. Cohen, and Μ. M. Fein, Inorg. Chem. 2, 1130 (1963). 35. T. L. Heying, J . W. Ager, S. L. Clark, R. P. Alexander, S. Papetti, J . A. Reid, and S. I. Trotz, Inorg. Chem. 2, 1097 (1963). 36. Μ. M. Fein and N. Schwartz, U.S. Patent 3,290,357 (1966). 37. L. I. Zakharkin, Yu. A. Chapovskii, V. A. Brattsev, and V. I. Stanko, Zh. Obshch. Khim. 36, 878 (1966). 38. V. I. Stanko, V. A. Brattsev, Ν. E. Al'perovich, and N. S. Titova, Zh. Obshch. Khim. 38, 1056 (1968). 39. L. I. Zakharkin, V. N. Kalinin, and A. I. L'vov, Izv. Akad. Nauk SSSR, Ser. Khim. p. 1091 (1966).

9. ICOSAHEDRAL CARBORANES

343

40. V. I. Stanko, A. I. Klimova, Yu. A. Chapovskii, and Τ. V. Klimova, Zh. Obshch. Khim. 36, 1779 (1966). 41. L. I. Zahkarkin and Yu. A. Chapovskii, Tetrahedron Lett. p. 1147 (1964). 42. Μ. M. Fein, M. S. Cohen, and C. W. Nebel, U.S. Patent 3,256,326 (1966). 43. V. Gregor, S. Hermanek, and J . Plesek, Collect. Czech. Chem. Commun. 33, 980 (1968). 44. D. Grafstein, J . Bobinski, J . Dvorak, J . E . Paustian, J . F . Smith, S. I. Karlan, C. Vogel, and Μ. M. Fein, Inorg. Chem. 2, 1125 (1963). 45. a). L. I. Zakharkin and V. N. Kalinin, Izv. Akad. Nauk SSSR, Ser. Khim. p. 586 (1966); b). L. I. Zakharkin and V. N. Kalinin, ibid. p. 2014. 46. J . F . Ditter, Ε. B . Klusmann, and R. E. Williams, U.S. Clearinghouse Fed. Sci. Tech. Inform., AD Rep. AD-670745 (1968). 47. S. Papetti, C. O. Obenland, and T. L. Heying, Ind. Eng. Chem., Prod. Res. Develop. 5, 334 (1966). 48. J . F . Sieckhaus, N. S. Semenuk, T. A. Knowles, and H. A. Schroeder, Inorg. Chem. 8, 2452 (1969). 49. a). F. N. Tebbe, P. M. Garrett, and M. F . Hawthorne, / . Amer. Chem. Soc. 90, 869 (1968); b). R. R. Rietz and M. F. Hawthorne, Inorg. Chem. 13, 755 (1973). 50. a). A. Kaczmarczyk, R. D. Dobrott, and W. N. Lipscomb, Proc. Nat. Acad. Sci. U.S. 48, 729 (1962); b). W. N. Lipscomb, Science 153, 373 (1966). 51. E. L. Muetterties and W. H. Knoth, "Polyhedral Boranes." Dekker, New York, 1968. 52. H. D. Kaesz, R. Bau, H. Beall, and W. N. Lipscomb, / . Amer. Chem. Soc. 89, 4218 (1967). 53. H. Hart and W. N. Lipscomb, / . Amer. Chem. Soc. 91, 771 (1969). 54. R. Hoffmann and W. N. Lipscomb, Inorg. Chem. 2, 231 (1963). 55. a). L. I. Zakharkin, V. N. Kalinin, and L. S. Podvisotskaya, Izv. Akad. Nauk SSSR, Ser. Khim. p. 1495 (1966); b). L. I. Zakharkin and V. N. Kalinin, Izv. Akad. Nauk SSSR, Ser. Khim. p. 194 (1969). 56. V. I. Stanko, G. A. Anorova, and Τ. V. Klimova, Zh. Obshch. Khim. 39,2143 (1969). 57. L. I. Zakharkin, Α. V. Grebennikov, L. E. Vinogradova, and L. A. Leites, Zh. Obshch. Khim. 38, 1048 (1968). 58. L. I. Zakharkin, V. I. Stanko, A. I. Klimova, and Yu. A. Chapovskii, Izv. Akad. Nauk SSSR, Ser. Khim. p. 2236 (1963). 59. a). V. I. Stanko, V. I. Bregadze, A. I. Klimova, O. Yu. Okhlobystin, A. N. Kashin, K. P. Butin, and I. P. Beletskaya, Izv. Akad. Nauk SSSR, Ser. Khim. p. 421 (1968); b). L. I. Zakharkin, V. N. Kalinin, and L. S. Podvisotskaya, ibid. p. 688; c). L. I. Zakharkin and Α. V. Kazantsev, Zh. Obshch. Khim. 37, 1211 (1967); d). L. I. Zakharkin, V. N. Kalinin, and L. S. Podvisotskaya, Izv. Akad. Nauk SSSR, Ser. Khim. p. 2661 (1968); e). A. N. Kashin, K. P. Butin, V. I. Stanko, and I. P. Beletskaya, ibid. p. 1917 (1969). 60. L. I. Zakharkin, Α. V. Grebennikov, and Α. V. Kazantsev, Izv. Akad. Nauk SSSR, Ser. Khim. p. 2077 (1967). 61. a). L. I. Zakharkin and Α. V. Kazantsev, Zh. Obshch. Khim. 35, 1123 (1965); b). L. I. Zakharkin, V. A. Brattsev, and Yu. A. Chapovskii, ibid. p. 2160. 62. O. Yu. Okhlobystin and L. I. Zakharkin, / . Organometal. Chem. 3, 257 (1965). 63. L. A. Fedorov, V. N. Kalinin, Ε. I. Fedin, and L. I. Zakharkin, Izv. Akad. Nauk SSSR, Ser. Khim. p. 849 (1970). 64. V. I. Pakhomov, Α. V. Medvedeo, V. I. Gregadze, and O. Yu. Okhlobystin, /. Organometal. Chem. 29, 15 (1971). 65. a). L. I. Zakharkin, V. I. Bregadze, and O. Yu. Okhlobystin, / . Organometal. Chem. 6, 228 (1966); b). L. I. Zakharkin, V. I. Bregadze, and O. Yu. Okhlobystin,

344

HERBERT BEALL

Zh. Obshch. Khim. 36, 761 (1966); c). L. I. Zakharkin, V. N. Kalinin, and L. S. Podvisotskaya, Izv. Akad. Nauk SSSR, Ser. Khim.?. 679 (1968); d). L. I. Zak­ harkin and L. S. Podvisotskaya, / . Organometal. Chem. 7, 385 (1967). 66. L. I. Zakharkin, V. I. Bregadze, and O. Yu. Okhlobystin, Izv. Akad. Nauk SSSR, Ser. Khim. p. 1539 (1964). 67. L. I. Zakharkin, V. I. Bregadze, and O. Yu. Okhlobystin, / . Organometal. Chem. 4, 244 (1965). 68. a). V. I. Stanko and A. I. Klimova, Zh. Obshch. Khim. 39, 1896 (1969); b). V. I. Stanko, A. I. Klimova, and A. N. Kashin, ibid. p. 1895. 69. M. F . Hawthorne, D. A. Owen, J . C. Smart, and P. M. Garrett, / . Amer. Chem. Soc. 93, 1362 (1971). 70. a). S. Bresadola, P. Rigo, and A. Turco, Chem. Commun. 20, 1205 (1968); b). J . C. Smart, P. M. Garrett, and M. F . Hawthorne, / . Amer. Chem. Soc. 91, 1031 (1969). 71. a). D. A. Owen and M. F . Hawthorne, / . Amer. Chem. Soc. 92, 3194 (1970); b). M. F . Hawthorne and D. A. Owen, ibid. 93, 873 (1971). 72. S. Bresadola, G. Cecchin, and A. Turco, Gazz. Chim. Ital. 100, 682 (1970). 73. a). C. M. Mitchell and F . G. A. Stone, / . Chem. Soc, D p. 1263 (1970); b). S. Bresadola, A. Frigo, B . Longato, and G. Rigatti, Inorg. Chem. 12, 2788 (1973); c). S. Bresadola and B . Longato, ibid. 13, 539 (1974). 74. L. I. Zakharkin and L. V. Orlova, Izv. Akad. Nauk SSSR, Ser. Khim. p. 2417 (1970). 75. a). V. I. Stanko, A. I. Klimova, and Τ. V. Klimova, Zh. Obshch. Khim. 37, 2236 (1967); b). V. I. Stanko, Yu. T. Struchov, A. I. Klimova, L. V. Bryukhova, and G. K. Semin, ibid. 36, 1707 (1966); c). L. I. Zakharkin and V. N. Kalinin, Dokl. Akad. Nauk SSSR 170, 92 (1966); d). L. I. Zakharkin and V. N. Kalinin, Izv. Akad. Nauk SSSR, Ser. Khim. p. 1311 (1965); e). L. I. Zakharkin and V. N. Kalinin, ibid. p. 575 (1966); f). L. I. Zakharkin, V. N. Kalinin, and V. S. Lozovskaya, ibid. p. 1780 (1968); g). V. I. Stanko and A. I. Klimova, Zh. Obshch. Khim. 38, 1194 (1968); h). V. I. Stanko, Yu. T. Struchkov, and A. I. Klimova, Zh. Strukt. Khim. 7, 629 (1966); i). V. I. Stanko, V. A. Brattsev, Τ. N. Vostrikova, and G. N. Danilova, Zh. Obshch. Khim. 38, 1348 (1968). 76. H. D. Smith, T. A. Knowles, and H. A. Schroeder, Inorg. Chem. 4, 107 (1965). 77. L. I. Zakharkin, V. I. Stanko, and A. I. Klimova, Izv. Akad. Nauk SSSR, Ser. Khim. p. 1946 (1966). 78. L. V. Bryukhova, V. I. Stanko, A. I. Klimova, N. S. Titova, and G. K. Semin, Zh. Strukt. Khim. 9, 39 (1968); b). V. G. Andrianov, V. I. Stanko, Yu. T. Struch­ kov, and A. I. Klimova, ibid. 8, 707 (1967); c). V. I. Stanko and Yu. T. Struchkov, Zh. Obshch. Khim. 35, 930 (1965). 79. a). V. I. Stanko and A. I. Klimova, Zh. Obshch. Khim. 36, 432 (1966); L. I. Zak­ harkin and V. N. Kalinin, Dokl. Akad. Nauk SSSR 169, 590 (1966); c). L. I. Zakharkin and V. N. Kalinin, Zh. Obshch. Khim. 37, 964 (1967); d). V. I. Stanko, A. I. Klimova, and N. S. Titova, ibid. 38, 2817 (1968). 80. C. O. Obenland and S. Papetti, / . Org. Chem. 31, 3868 (1966). 81. V. I. Stanko and Yu. V. Gol'tyapin, Zh. Obshch. Khim. 39, 711 (1969). 82. J . F . Sieckhaus, N. S. Semenuk, T. A. Knowles, and H. A. Schroeder, U.S. Clearing­ house Fed. Sci. Tech. Inform., AD Rep. AD-665306 (1968) (Avail. CFSTI). 83. L. A. Leites, N. A. Ogorodnikova, and L. I. Zakharkin, J . Organometal. Chem. 15, 287 (1968). 84. a). L. I. Zakharkin and V. N. Kalinin, Dokl. Akad. Nauk SSSR 173, 1091 (1967); b). L. I. Zakharkin, V. I. Stanko, and A. I. Klimova, Izv. Akad. Nauk SSSR, Ser. Khim. p. 771 (1964); c). H. A. Schroeder and G. D. Vickers, Inorg. Chem. 2, 1317 (1963); d). L. I. Zakharkin and N. A. Ogorodnikova, / . Organometal. Chem. 12, 13 (1968).

9. ICOSAHEDRAL CARBORANES

345

85. a). H. A. Schroeder, T. L. Heying, and J . R. Reiner, Inorg. Chem. 2, 1092 (1963); b). Μ. V. Sobolevskii, A. F. Zhigach, I. G. Sarishvili, K. P. Grinevich, and S. S. Beyul, Plast. Massy 4, 19 (1966). 86. L. I. Zakharkin and V. N. Kalinin, Zh. Obshch. Khim. 36, 362 (1966). 87. a). H. A. Schroeder, J . R. Reiner, R. P. Alexander, and T. L. Heying, Inorg. Chem. 3, 1464 (1964); b). L. I. Zakharkin and L. S. Podvisotskaya, Izv. Akad. Nauk SSSR, Ser. Khim. p. 1464 (1965); c). V. I. Stanko, G. A. Anorova, and T. P. Klimova, Zh. Obshch. Khim. 39, 1073 (1969); d). L. I. Zakharkin, V. N. Kalinin, and G. G. Zhigareva, Izv. Akad. Nauk SSSR, Ser. Khim. p. 2081 (1967). 88. S. Kongpricha and H. A. Schroeder, Inorg. Chem. 8, 2449 (1969). 89. a). V. I. Stanko and G. A. Anorova, Zh. Obshch. Khim. 37, 507 (1967); b). V. I. Stanko and G. A. Anorova, ibid. p. 2359; c). L. I. Zakharkin, G. G. Zhigareva, and Α. V. Kazantsev, ibid. 38, 89 (1968). 90. L. I. Zakharkin and N. A. Ogorodnikova, Izv. Akad. Nauk SSSR, Ser. Khim. p. 346 (1966). 91. a). R. P. Alexander and H. A. Schroeder, Inorg. Chem. 2, 1107 (1963); b). L. I. Zakharkin and Α. V. Grebennikov, Izv. Akad. Nauk SSSR, Ser. Khim. p. 696 (1967); c). L. I. Zakharkin and Α. V. Kazantsev, ibid. p. 2190 (1965); d). L. I. Zakharkin, ibid. p. 158; e). L. I. Zakharkin, Tetrahedron Lett. p. 2255 (1964). 92. a). Μ. M. Fein and M. S. Cohen, U.S. Patent 3,376,347 (1968); b). L. I. Zak­ harkin and Α. V. Kazantsev, Zh. Obshch. Khim. 37, 1211 (1967). 93. M. F . Hawthorne, Τ. E. Berry, and P. A. Wegner, / . Amer. Chem. Soc. 87, 4746 (1965). 94. a). Ν. K. Hota and D. S. Matteson, / . Amer. Chem. Soc. 90, 3570 (1968); b). D. S. Matteson and R. A. Davis, Inorg. Chem. 13, 859 (1974). 95. A. I. L'vov and L. I. Zakharkin, Izv. Akad. Nauk SSSR, Ser. Khim. p. 2653 (1967). 96. a). V. I. Stanko and Α. V. Bobrov, Zh. Obshch. Khim. 35, 2003 (1965); b). L. I. Zakharkin and V. N. Kalinin, Dokl. Akad. Nauk SSSR 164, 577 (1965); c). L. I. Zakharkin and V. N. Kalinin, Izv. Akad. Nauk SSSR, Ser. Khim. p. 2206 (1965); d). L. I. Zakharkin, V. I. Stanko, and A. I. Klimova, Zh. Obshch. Khim. 35, 394 (1965). 97. a). L. I. Zakharkin, V. N. Kalinin, and L. S. Podvisotskaya, Izv. Akad. Nauk SSSR, Ser. Khim. p. 1713 (1965); b). L. I. Zakharkin, V. N. Kalinin, and L. S. Podvisotskaya, Zh. Obshch. Khim. 36, 1786 (1966). 98. L. I. Zakharkin and V. N. Kalinin, Izv. Akad. Nauk SSSR, Ser. Khim. p. 937 (1967). 99. W. E. Hill, Inorg. Chem. 7, 222 (1968). 100. Μ. M. Fein and J . E. Paustian, U.S. Patent 3,217,031 (1965). 101. L. I. Zakharkin and Α. V. Kazantsev, Zh. Obshch. Khim. 36, 1285 (1966). 102. a). V. I. Stanko and A. I. Klimova, Zh. Obshch. Khim. 35, 1141 (1965); b). L. I. Zakharkin and Α. V. Kazantsev, Izv. Akad. Nauk SSSR, Ser. Khim. p. 568 (1966); c). L. I. Zakharkin, Α. V. Grebennikov, Α. V. Kazantsev, and A. I. L'vov, ibid. p. 2079 (1967). 103. a). L. I. Zakharkin and Α. V. Kazantsev, Zh. Obshch. Khim. 36, 945 (1966); b). L. I. Zakharkin and Α. V. Kazantsev, ibid. 37, 554 (1967). 104. L. I. Zakharkin and A. I. L'vov, Zh. Obshch. Khim. 37, 1217 (1967). 105. L. I. Zakharkin, Dokl. Akad. Nauk SSSR 162, 817 (1965). 106. D. Grafstein and J . Dvorak, U.S. Patent 3,226,429 (1965). 107. V. I. Stanko, V. A. Brattsev, Ν. E. Al'perovich, and N. S. Titova, Zh. Obshch. Khim. 36, 1862 (1966). 108. a). L. I. Zakharkin and V. N. Kalinin, Izv. Akad. Nauk SSSR, Ser. Khim. p. 1423 (1968); b). L. I. Zakharkin and A. I. L'vov, Zh. Obshch. Khim. 37, 742 (1967). 109. L. I. Zakharkin and A. I. L'vov, Izv. Akad. Nauk SSSR, Ser. Khim. p. 151 (1966).

346

HERBERT BEALL

110. J . R. Reiner, R. P. Alexander, and H. A. Schroeder, Inorg. Chem. 5, 1460 (1966). 111. L. I. Zakharkin, A. I. L'vov, and L. S. Podvisotskaya, Izv. Nauk SSSR, Ser. Khim. p. 1905 (1965). 112. a). N. R. Fetter, Can. J . Chem. 44, 1463 (1966); b). L. I. Zakharkin and Α. V. Grebennikov, Izv. Akad. Nauk SSSR, Ser. Khim. p. 1376 (1967). 113. a). V. I. Stanko and G. A. Anorova, Zh. Obshch. Khim. 36, 946 (1966); b). V. I. Stanko, G. A. Anorova, and Τ. V. Klimova, ibid. p. 1774. 114. L. I. Zakharkin, Α. V. Grebennikov, and L. A. Savina, Izv. Akad. Nauk SSSR, Ser. Khim. p. 1130 (1968). 115. V. I. Stanko and A. I. Klimova, Zh. Obshch. Khim. 35, 1503 (1965). 116. V. I. Stanko and A. I. Klimova, Zh. Obshch. Khim. 36, 159 (1966). 117. a). A. L. Klebanskii, V. F . Gridina, L. P. Dorofeenko, Κ. E. Krupnova, G. E. Zakharova, and Ν. I. Shkambarnaya, Khim. Geterotsikl. Soedin. 3, 570 (1967); b). S. Papetti and T. L. Heying, Inorg. Chem. 2, 1105 (1963); c). R. M. Salinger and C. L. Frye, ibid. 4, 1815 (1965); d). S. Papetti and T. L. Heying, ibid. 3, 1448 (1964); e). H. A. Schroeder, S. Papetti, R. P. Alexander, J . F. Sieckhaus, and T. L. Heying, ibid. 8, 2444 (1969). 118. S. Papetti, Β . B . Schaeffer, H. J . Troscianiec, and T. L. Heying, Inorg. Chem. 3, 1444 (1964). 119. a). Μ. M. Fein, N. Schwartz, and S. I. Karlan, French Patent 1,436,574 (1966); b). N. Mayes and M. S. Cohen, J . Polym. Sci., Part A-1 5, 365 (1967); c). N. Schwartz, E. A. O'Brien, S. L. Karlan, and Μ. M. Fein, Inorg. Chem. 4, 661 (1965). 120. A. L. Klebanskii, V. F . Gridina, L. P. Dorofeenko, A. F. Zhigach, Ν. V. Kozlova, E. Krupnova, G. E. Zahharova, and Ν. I. Shkambarnaya, Khim. Geterotsikl. Soedin. 4, 976 (1968). 121. a). Μ. M. Fein, J . Green, and N. Mayes, U.S. Patent 3,354,193 (1967); b). Μ. M. Fein, J . Green, and E. L. O'Brien, U.S. Patent 3,355,478 (1967); c). A. S. Shapatin, S. A. Golubtsov, A. A. Solov-ev, A. F. Zhigach, and V. N. Siryatskaya, Plast. Massy 12, 19 (1965). 122. a). S. Bresadola, F . Rossetto, and G. Tagliavini, Chem. Commun. p. 623 (1966); b). S. Bresadola, F . Rossetto, and G. Tagliavini, Eur. Polym. J . 4, 75 (1968); c). S. Bresadola, F . Rossetto, and G. Tagliavini, Ann. Chim. (Rome) 58, 597 (1968). 123. V. I. Bregadze and O. Yu. Okhlobystin, Izv. Akad. Nauk SSSR, Ser. Khim. p. 2084 (1967). 124. J . M. Kauffman, J . Green, M. S. Cohen, Μ. M. Fein, and E. L. Cottrill, / . Amer. Chem. Soc. 86, 4210 (1964). 125. L. I. Zakharkin and A. I. L'vov, Zh. Obshch. Khim. 36, 761 (1966). 126. L. I. Zakharkin and V. N. Kalinin, Zh. Obshch. Khim. 35, 1882 (1965). 127. J . L. Boone, R. J . Brotherton, and L. L. Petterson, Inorg. Chem. 4, 910 (1965). 128. R. P. Alexander and H. A. Schroeder, Inorg. Chem. 5, 493 (1966). 129. a). H. D. Smith, / . Amer. Chem. Soc. 87, 1817 (1965); b). L. I. Zakharkin and G. G. Zhigareva, Izv. Akad. Nauk SSSR, Ser. Khim. p. 932 (1965); c). L. I. Zak­ harkin and G. G. Zhigareva, Zh. Obshch. Khim. 37, 1791 (1967). 130. a). H. D. Smith, Inorg. Chem. 8, 676 (1969); b). R. Zaborowski and K. Cohn, Inorg. Chem. 8, 678 (1969); c). V. I. Bregadze, D. N. Sadzhaya, and O. Yu. Okhlo­ bystin, Soobshch. Akad. Nauk Gruz. SSR 63, 77 (1971). 131. a). L. I. Zakharkin and G. G. Zhigareva, Zh. Obshch. Khim. 39, 1894 (1969); b). L. I. Zakharkin and G. G. Zhigareva, ibid., 40, 2333 (1970). 132. V. A. Brattsev and V. I. Stanko, Zh. Obshch. Khim. 40, 1664 (1970). 133. H. D. Smith, C. O. Obenland, and S. Papetti, Inorg. Chem. 5, 1013 (1966). 134. L. I. Zakharkin and G. G. Zhigareva, Izv. Akad. Nauk SSSR, Ser. Khim. p. 1358 (1967).

9. ICOSAHEDRAL CARBORANES

347

135. Ν. S. Semenuk, S. Papetti, and H. A. Schroeder, Inorg. Chem. 8, 2441 (1969). 136. a). H. D. Smith, M. A. Robinson, and S. Papetti, Inorg. Chem. 6, 1014 (1967); b). L. I. Zakharkin and G. G. Zhigareva, Zh. Obshch. Khim. 37, 2781 (1967). 137. H. D. Smith and L. F . Hohnstedt, Inorg. Chem. 7, 1061 (1968). 138. a). J . Green, N. Mayes and M. S. Cohen, / . Polym. Sci., Part A 2, 3113 (1964); b). J . Green, N. Mayes, A. P. Kotolby, and M. S. Cohen, ibid. p. 3135; c). J . Green, N. Mayes, A. P. Kotloby, Μ. M. Fein, E. L. O'Brien, and M. S. Cohen, /. Polym. Sci., Part Β 2, 109 (1964); d). A. F . Zhigach, Μ. V. Sobolevskii, I. G. Sarishvili, and B . A. Akimov, Plast. Massy 5, 20 (1965); e). I. G. Sarishvili, A. F . Zhigach, Μ. V. Sobolevskii, B . A. Akimov, and Ε. M. Kozyreva, ibid. 10, 37 (1967). 139. V. V. Korshak, S. Vinogradova, P. M. Valetskii, V. I. Stanko, Τ. N. Vostrikova, and L. A. Glivka, Otkrytiya Izobret., Prom. Obraztsy, Povarnye Znaki 47, 206 (1970). 140. V. Gregor, J . Plesek, and S. Hermanek, Int. Union Pure Appl. Chem., Int. Symp. MacromoL Chem., 1965. 141. a). T. J . Klingen and J . R. Wright, Mol. Cryst. Liquid Cryst. 13, 173 (1971); b). J . R. Wright and T. J . Klingen, / . Inorg. Nucl. Chem. 32, 2853 (1970); c). A. F . Zhigach, Yu. G. Chikishev, V. N. Siryatskaya, S. L. Sosin, and V. V. Korshak, Vysokomol. Soedin., Ser. Β 12, 771 (1970). 142. a). T. L. Heying, S. Papetti, and O. G. Schaffling, U.S. Patent 3,388,090 (1968); b). T. L. Heying, S. Papetti, and O. G. Schaffling, U.S. Patent 3,388,091 (1968); c). T. L. Heying, S. Papetti, and O. G. Schaffling, U.S. Patent 3,388,092 (1968); d). S. Papetti, Β . B . Schaeffer, A. P. Grey, and T. L. Heying, / . Polym. Sci., Part A-l 4, 1623, (1966); e). H. A. Schroeder, Inorg. Macromol. Rev. 1, 45 (1970). 143. a). A. D. Delman, A. A. Stein, J . J . Kelly, and Β . B . Simms, / . Appl. Polym. Sci. 11, 1979 (1967); b). J . Green and N. Mayes, J . Macromol. Sci. Chem. 1, 135 (1967); c). L. H. Sperling, S. L. Cooper, and Α. V. Tobolsky, / . Appl. Polym. Sci. 10, 1725 (1966); d). L. H. Sperling, E. J . Zaganiaris, and Α. V. Tobolsky, U.S. Clearing­ house Fed. Sci. Tech. Inform., AD Rep. AD-656049 (1967) (Avail. CFSTI); e). E. J . Zaganiaris, L. H. Sperling, and Α. V. Tobolsky, J . Macromol. Sci. Chem, 1, 1111 (1967); f). H. A. Schroeder, O. G. Schaffling, Τ. B . Larchar, F. F. Frulla, and T. L. Heying, Rubber Chem. Technol. 39, 1184 (1966). 144. a). N. S. Semenuk, S. Papetti, and H. A. Schroeder, Angew. Chem., Int. Ed. Engl. 6, 997 (1967); b). S. Bresadola, F. Rossetto, and G. Tagliavini, Chim. Ind. (Milan) 50, 452 (1968). 145. a). R. A. Wiesboeck, and M. F. Hawthorne, / . Amer. Chem. Soc. 86, 1642 (1964); b). P. M. Garrett, F. N. Tebbe, and M. F . Hawthorne, ibid. p. 5016; c). M. F. Hawthorne, P. A. Wegner, and R. C. Stafford, Inorg. Chem. 4, 1675 (1965); d). M. F . Hawthorne, D. C. Young, P. M. Garrett, D. A. Owen, S. G. Schwerin, F. N. Tebbe, and P. A. Wegner, / . Amer. Chem. Soc. 90, 862 (1968); e). L. I. Zakharkin and V. N. Kalinin, Izv. Akad. Nauk SSSR, Ser. Khim. p. 462 (1967). 146. D. V. Howe, C. J . Jones, R. J . Wiersema, and M. F . Hawthorne, Inorg. Chem. 10, 2516 (1971). 147. a). M. F. Hawthorne, D. C. Young, and P. A. Wegner, / . Amer. Chem. Soc. 87, 1818 (1965); b). L. I. Zakharkin, Ε. I. Kukulina, and L. S. Podvisotskaya, Izv. Akad. Nauk SSSR, Ser. Khim. p. 1866 (1966); c). J . S. Roscoe, S. Kongpricha, and S. Papetti, Inorg. Chem. 9, 1561 (1970). 148. a). M. F. Hawthorne and P. A. Wegner, / . Amer. Chem. Soc. 87, 4392 (1965); b). M. F. Hawthorne and P. A. Wegner, ibid., 90, 896 (1968).