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Molybdenum and tungsten Cp∗ complexes that contain 2,2′-diamidodiphenylamido or 2-amido-2′-oxydiphenylamido ligands
PolyhedronVol. 17, No. 5-6, pp. 749 758, 1998
~
Pergamon PII : S0277-5387(97)00394-X
',c 1998 Elsevier Science Ltd All rights reserved. Printed in Great Britain 0277 5387/98 $19.00+0.00
Molybdenum and tungsten Cp* complexes that contain 2,2'-diamidodiphenylamido or 2amido-2'-oxydiphenylamido ligands Shi'ang Cai, Richard R. Schrock,* Rhett R. Kempe and W. M. Davis Department of Chemistry 6-331, Massachusetts Institute of Technology Cambridge, MA 02139, U.S.A.
(Received 25 April 1997; accepted 1 August 1997)
Abstract Cp*MC14
compounds (M = Mo or W) react with 2-amino-2'-hydroxydiphenylamine ([H2NNHOH]) to yield complexes of the type Cp*M[HNNO]CI. An X-ray study of the one electron reduction product, {Na(C2Hs)20}{Cp*Mo[HNNO]C1}, showed it to contain square pyramidal {Cp*Mo[HNNO]C1] ions weakly connected by bridging Na(ether) units. Cp* W[HNNO]C1 could be oxidized readily by AgOTf in acetonitrile to produce {Cp*W[HNNO]C1} +OTf . Both Cp*M[HNNO]CI compounds are reduced by hydrazinc to give the diamagnetic compound, Cp*M[HNNO](NH3). An X-ray structure of Cp*Mo[HNNO](NH3) showed that the almost planar [HNNO] 3 ligand and the ammonia ligand occupy the four basal positions in an approximately square pyramidal "piano stool" complex. Red crystalline Cp*W[HNNNH]CI ([HNNNH] 3 = [(2-NHC6H4)2N] 3-) could be prepared from Cp*WC14 and 2,2'-diaminodiphenylamine. It can be oxidized with AgOTf or NOPF6 to yield {Cp*W[HNNNH]CI}X (X = OTf or PF0. {Cp*W[HNNNH]CI]PF6 reacts with three equivalents of NH2NMe2 to afford Cp*W[HNNNH](NNMe2), with four equivalents of isopropylamine to produce Cp*W[HNNNH](N-i-Pr), and with water in the presence of K2CO3 to yield Cp*W[HNNNH](O). Cp*W[(HNNNH]CI reacts with dimethyl zinc at 80 '= to give Cp*W[HNNNH]Me, which can be subsequently oxidized by silver triflate to give {Cp*W[HNNNH]Me}OTf. Deprotonation of {Cp*W[HNNNH]Me}OTf with DBU yielded an imido complex, Cp*W[(2-N-C6H4)(2'-NHC6H4)N]Me via loss of one of the two ligand NH protons. '.f211998 Elsevier Science Ltd. All rights reserved
Keywords: molybdenum : tungsten ; 2,2'-diamidodiphenylamido; 2-amido-2'-oxydiphenylamido.
In the past few years we have synthesized and explored the chemistry of relatively high oxidation state tungsten or molybdenum complexes that will activate and reduce dinitrogen. In a series of studies we focused on complexes that contain the Cp*MMe~ core (M = W [1 5], Mo [3,6,7], or Re[8]). Some of the results that have emerged from these studies are as follows: (i) metals in a relatively high oxidation state (e.g. W(III) or W(IV)) can bind N2 or partially reduce (N2Hx) ligands ; (ii) a 2~, 1a arrangement of orbitals in such circumstances is favorable for stabilizing N2Hx ligands; and (iii) a complex that contains bound hydrazine is a likely intermediate in which the N - - N bond is cleaved to give ammonia. Recent investigations of the chemistry of tungsten and molybdenum phosphine complexes that is relevant to dinitrogen fixation has also begun to focus on the
* A u t h o r to w h o m c o r r e s p o n d e n c e s h o u l d be a d d r e s s e d .
"mid" oxidation states for binding partially reduced (N2H0 ligands [9]. Unfortunately, there is at least one significant disadvantage to complexes that contain the Cp*MMe3 core. If we are to have any hope of reaching our longterm goal of developing a catalytic system for the reduction of dinitrogen using protons and electrons, methyl ligands eventually are protonated and lost as methane. Complexes that contain monodentate alkoxide ligands [10] did not prove to be suitable, in part because alkoxides also are readily protonated and can undergo ligand redistribution reactions that significantly complicate the chemistry in which we are interested. Therefore we looked for multidentate trianionic ligands that could take the place of the three methyl groups in the Cp*MMe3 core and that would be less susceptible than methyl ligands toward protonation and subsequent dissociation from the metal. 2,2'-Diaminodiphenylamine [11] and 2-amino-2'hydroxydiphenylamine can be prepared by reducing
749
750
S. Cai et al.
the corresponding nitro compounds [12]. We felt that trianions derived from such compounds, [HNNNH] 3or [HNNO] 3 (see below), would bind to Mo or W to yield complexes that contain Cp*M(HNNNH) or Cp*M(HNNO) cores. The o-phenylene rings should enforce planarity of the ligand system and therefore should encourage formation of pseudo five-coordinate complexes having a "piano stool" geometry. They also should discourage protonation of the amido nitrogen atoms. In this paper we report the synthesis of MCp*[HNNO] (M = Mo or W) and WCp*[HNNNH] complexes, X-ray structures of two MoCp*[HNNO] derivatives, and some chemistry that suggests that such ligands may prove useful for high oxidation state Mo or W chemistry.
N/
-N
N/
\
H
H
-O
H
[HNNO]3-
[HNNNH] 3-
RESULTS AND DISCUSSION Complexes contain&9 (M = Mo, W)
the
Cp*M[HNNO]
Core
Cp*MoC14 reacts with 2-amino-2'-hydroxydiphenylamine in the presence of three equivalents of triethylamine to yield the 2-amido-2'-oxydiphenylamido ([HNNO] 3 ) derivative la [eqn (1)] as brown-black microcrystals in 65% isolated yield. An analogous reaction starting with Cp*WC14 yielded Cp*W[HNNO]C1 (lb). Both la and lh show ESR signals at g ~ 2, consistent with the presence of one unpaired electron. Although resonance forms can be drawn in which the metal is in a more reduced state, we prefer to view these as d ~M(V) complexes.
Cp*MCI4 + NH 2
HO H
+ 3 Et3N
~
- 3Et3HC1 '~
~
Cp*
(1)
!
'"'" IVI'"'
CI
d ~
M:Mo (la); W (1 b).
Reaction of la with CpzCo yields a diamagnetic species that we formulate as the d 2 complex, {Cp2Co}{Cp*Mo[HNNO]CI} (2) formed by one elec-
tron reduction of la (Scheme 1). Reduction of la with sodium amalgam in THF yields an analogous species (3) that is isolated as a sodium salt containing one equivalent of diethyl ether. The proton on nitrogen in the HNNO ligand could be observed at 7.80 ppm in the proton NMR spectrum of 3 as a broad singlet, but not in 2 (at 22':C), perhaps because in 2 the NH proton cannot be differentiated from aryl protons between 7.20 and 6.00 ppm. An X-ray study of 3 showed it to contain approximately square pyramidal {Cp*Mo[HNNO]CI} ions weakly connected by bridging Na(ether) units (Fig. 1, Table 1) in a manner such that the O(2)--Na(I)--Na(2)--O(3) axis serves as a C: axis. The [HNNO] 3 ligand is approximately planar. Unfortunately, the structure had to be refined with the Cp* and phenyl rings as rigid groups, and therefore the quality is not high. The Na--C1 bond lengths are ~2.70 A, but the Na(1)--N(2) distance (2.55 A) and Na(2)--O(1) distance (2.51 A) suggest that these interactions are significant and that the sodium ions therefore are pseudo five-coordinate. The core bond lengths and angles in the {Cp*Mo [HNNO]CI}- ion are shown in Fig. 2 in order to illustrate that the approximately square pyramidal MoN2OCI core geometry is roughly the same as that found for a more accurately determined structure discussed below. Reduction of lb proceeds similarly to yield what appears, by proton NMR, to be the tungsten analog of 2, but this compound was not characterized further. Cp*W[HNNO]C1 could be oxidized readily by AgOTf in acetonitrile to produce {Cp*W[HNNO] CI} + OTf (4) essentially quantitatively. The NH proton in 4 was located at 11.37 ppm in the proton NMR spectrum. We assume that there is no room for the triflate ion to bind strongly to the metal and therefore have formulated 4 as an ionic species. In contrast, la was not oxidized under similar conditions to an analogous Mo(VI) species. Compounds la and lb are both reduced by hydrazine (2 equiv.) to give diamagnetic compounds with the formula Cp*M[HNNO](NH3) (5a and 5b, respectively). The only other observable product of these high yield reactions was N,H~ (according to N M R spectra), presumably as the chloride salt. The proton on nitrogen in the HNNO ligand and the ammonia protons could not be observed readily in either 5a or 5b as a consequence of facile proton exchange between these sites at room temperature. At low temperature the rate of the exchange process is slow enough that the HNNO proton can be observed near 8 ppm (8.34 ppm in 5a: 8.27 ppm in 5b) and the NH3 proton around 3 ppm (2.96 ppm in 5a ; 3.68 ppm in 5b). 5a is also formed upon addition of excess hydrazine to 3. We speculate that the mode of formation of compounds 5a and 5b from la and lb involves formation and decomposition of intermediate hydrazido(1-) species, Cp*M[HNNO](N2H3), as shown in eqns (2) and (3). This proposal is based on the fact that the W(V) complex, Cp*WMe3(N,H0, which is pro-
751
Molybdenum and tungsten Cp* complexes Cp*
I
HN .......... Mo ~ CI [CoCp2]
N
[NaO(C2Hs)2Cp*M°[HNNO]CI }2 (3)
~
a (Hg) ~ + CoCp2
+ excess N2H 4
2
/''(p*
HN ........... M
CI
N AgOTf "x,• "~
+ 2 N2H4/
- NzHsC1 Cp*
I
HN ...........M ~
/x
la (M = Mo) lb (M = W)
"AgO
Cp*
NH3
o
5a (M = Mo) 5b (M = W)
Scheme, I.
2.51
it
Na( 1)
Fig. 1. Molecular structure of {Na[O(C~H~)z]Cp*Mo[(2-NH-CoH4I(2"-O-C6H4)N]CI}2 (3). Hydrogen aloms are omitted for clarity,
posed to be formed upon deprotonation of [Cp*WMe3(NeH4)] +, decomposes to yield 0.5 equiv, of Cp*Me~W---NNH2, 0.5 equiv, of C p * M % W
= N H , and 0.5 equiv, of NH~ [1]. Since the proposed C p * M [ H N N O ] ( N 2 H 0 compounds would also contain the metal in the M(V) oxidation state, we propose
S. Cai et al.
752
Table 1. Selected bond lengths (A) and bond angles (:) in INa[O(C:Hs)2]Cp*Mo[HNNO]C1)_~ (3)
Table 2. Selected bond lengths (A) and bond angles ( ) in Cp*Mo[HNNO](NH0 (5a)
Mo--O(1) Mo--N(2) Na(I)--CI Na(I)--N(2) Na(1)--O(2)
2.13(2) 1.94(2) 2.70(2) 2.55(2) 2.20(4)
Mo--N(I) Mo--C1 Na(2)--CI Na(2)--O(l) Na(2)--O(3)
Mo--O(l) Mo--N(2) Mo--C(13) Mo--C(17) Mo--2(21)
O(I)--Mo--N(I) N(I)--Mo--N(2) N(2)--Mo--CI Na(1)--C1--Na(2)
73(1) 81(1) 80.6(6) 85.1(4)
O(I)--Mo--CI 84.9(5) O(1)--Mo--N(I) 77.0(2) N(I)--Mo--CI 131.1(4) N(I)--Mo--N(3) 87.9(2) N(2)--Mo--O(I} 128.7(9) N(3)--Mo--O(I) 126.0(2) CI--Na(1 )--CI' 95.4(7)
2.01(1) 2.510(4) 2.72(2) 2.51(2) 2.36(3)
that they also are likely to be unstable with respect to an intermolecular decomposition reaction shown in eqn (3). However, details of the decomposition reaction are unclear at this stage. It is also not clear why M(IV) ammonia complexes are formed rather than M = NNH2 or M = NH species. Cp* M[HNNO]CI + 2N2H4
N2HsCI+"Cp*M[HNNO](N2H3)'"
(2)
"Cp*M[HNNO](N2H3)'" Cp*M[HNNO](NH3) + 0.5N2
(3)
Crystals of 5a suitable for X-ray studies were obtained by recrystallization from an ether solution layered with pentane. The core structure of 5a (Fig. 3) is similar to that found in 3 (Fig. 2). Relevant bond lengths and angles are listed in Table 2 and the core of 5a is compared to that of 3 in Fig. 2. The 2-amidophenyl-2'-oxydiphenylamido ligand and the ammonia ligand occupy the four basal positions in a square pyramidal or "piano stool" arrangement typically found for pseudo-five-coordinate monocylopentadienyl complexes [13]. The [HNNO] 3 ligand is close to being planar and the two M o - - N and one M o - - O bonds are all essentially the same length and relatively short (2.02 to 2.05 /k). The N(3)--Mo--N(2) and N ( 2 ) - - M o - - O ( I ) bond angles are essentially equal, but the N(3)--Mo--N(1) bond
73o
2.049(5) 2.024(6) 2.238(7) 2.435(7) 2.208(7)
Mo--N(I) Mo--NI3) Mo--C(15) Mo--C(19)
O(1)--Mo--N(2) 77.1(2) N(2)--Mo--N(3) 75.3(2) N(2)--Mo--N(1) 131.3(2)
angle is larger than the O ( 1 ) - - M o - - N ( I ) bond angle by ~ 10~:, perhaps because of steric repulsion between the proton on N(3) and the protons on ammonia. The Mo--N(1) distance (2.225(6) A) is what one might expect for a dative M o - - N bond. The Cp* ligand is coordinated in an acentric fashion, with the Mo--C(17) distance being statistically longer that the other M o - - C distances. This circumstance is not unusual [14] and probably can be ascribed to greater repulsive forces between the ammonia ligand and the Cp* ligand compared to those between the flat HNNO ligand and the Cp* ligand. The protons on the ammonia ligand were not located in the X-ray study.
Synthesis and reactA, iO' o/ complexes containing the Cp*W[(2-NH-C6H4)_~N] core Cp*W[HNNNH]C1 (6; Scheme 2 ; [HNNNH] 3 = [(2-NHC6H4)2N]3 ) could be prepared from Cp*WCl4 and 2,2'-diaminodiphenylaminein the presence of at least three equivalents of triethylamine. Compound 6 is a red crystalline solid that is relatively soluble in CH2C12 and THF, but sparingly soluble in CH3CN and hydrocarbons. It can be stored in air over a period of several weeks without significant decomposition. It does not react with water or methanol in the presence of triethylamine, nor does it react readily with NH3 or N_~H+ Compound 6 was not reduced by cobaltocene or zinc amalgam. It did react with excess sodium
8,°
3
C1
2.226(6) 2.017(6) 2.356(7) 2.296(7)
5a
N
O-Mo-N =129°;N-Mo-C1= 131° O-Mo-N =126°; N-Mo-N= 131° Fig. 2. A comparison of bond lengths and angles in 3 and 5a.
Molybdenum and tungsten Cp* complexes
753
C(~7)
N(I) Fig. 3. Molecular structure of Cp*Mo[(2-NH-C~HD(Y-O-C~HDN](NH3) (Sa). Hydrogen atoms are omitted for clarity.
Cp*
Cp* 1 ]+ + H2NNMe2 HN ........W - - CI/ X " ~ HN
AgOTf HN
........
W ~ CI
Cp*
I
........
W - - - NNMe2
or NOPF6
6 7a (X = OTf)
~ +Zn(CH3)2
7b (X = PFs)
N ~ + H2NCHMe2
\
K2CO3 ~ H20 Cp*
Cp*
f
1
HN ........W ~
CH3
HN ........W --- NCHMe2
9
8b
+ AgOTf or HOTf
Cp*
i
I
HN ........W ---" O
10
~
Cp*
Cp*
+ DBU
N~
4
l
W~CH 3
+ HOTf 11
12 Scheme. 2.
amalgam in T H F to produce an extremely air-sensitive diamagnetic species in low yield (30% from acetonitrile), but this product was not characterized. C o m p o u n d 6 can be oxidized readily, For example, it reacts cleanly with A g O T f or NOPF~ to afford {Cp*W[HNNNH]C1}X (X = OTf, 7a ; PF~, 7b) quantitatively, Both compounds are soluble in acetonitrile, but insoluble in other c o m m o n organic solvents. 'H N M R spectra of the two in CD3CN are ahnost identical, consistent with their proposed ionic nature. The [ H N N N H ] 3- ligand N H resonance is found as a broad
singlet at 10.22 ppm in the proton N M R spectrum in CD~CN. Compound 7b reacts with three equivalents of N H z N M e : to afford C p * W [ H N N N H ] ( N N M e 2) (Sa) in moderate (37% isolated) yield. C o m p o u n d 7b also reacts with four equivalents of isopropylamine to produce Cp*W[HNNNH](N-i-Pr) (8b), and with water in the presence of KzCO3 to yield C p * W [ H N N N H ] ( O ) (9). Proton N M R spectra of 8 and 9 in C~D6 reveal the [ H N N N H ] 3- ligand N H resonance at ~6.5 ppm. Compound 6 reacts with dimethyl zinc slowly at
754
S. Cai et al.
room temperature, and at 80': Cp*W[HNNNH]Me (10) is formed in good yield (67% isolated) in 1 h. Compound 10 is oxidized quantitatively by silver triflate to give {Cp*W[HNNNH]MelOTf (11). Interestingly, an attempt to protonate 10 with one equivalent of triflic acid in CH2C12 led (slowly over a period of 3 days) to its oxidation to give 11 in moderate yield (65% isolated). The proton NMR spectrum of 11 in CD3CN showed a resonance at 0.71 ppm, for the methyl group. Only four different aromatic protons were observed, consistent with the molecule having mirror symmetry. Compound 11 is a rare example of a cationic W(VI) alkyl complex (cf. [Cp*WMes]+). [15]. Deprotonation of 11 with DBU did not give Cp*W[HNNNH](CH2), but an imido complex, Cp*W[(2-N-C6H4)(2'-NH-C6H4)N]Me (12), formed via loss of one of the two ligand NH protons. The NMR spectrum of 12 is relatively complex, as expected for a molecule having no symmetry. Normally eight proton resonances are observed in the aromatic region, but if 12 is contaminated with a trace of a proton source, even DBUHOTf, only four different aromatic proton resonances are observed, consistent with protonation and deprotonation of 12 being a fast and reversible process. Addition of one equivalent of HOTf to 12 yields 11 quantitatively. Formation of 12 should be compared to deprotonation of [Cp*WMes] + to yield unstable Cp*WMe3(CH2) [15].
CONCLUSIONS Multidentate amido ligands that contain o-phenylene links between amido nitrogens show some promise as supporting ligands for high oxidation state Cp*Mo or Cp*W chemistry. Among the interesting features of complexes that contain such ligands are the planar tridentate ligand backbone, the stability of the backbone to proton abstraction and cleavage reactions, and the ability of several complexes to be smoothly oxidized or reduced. For steric reasons, the parent (proton-substituted) versions of the two ligands described here are likely to be the only ones that can be put on Cp*M complexes to give approximately square pyramidal complexes. Conversely, more steric protection against bimolecular reactions is likely to be required if multidentate amido ligands are employed in the absence of other bulky ligands. In this context it should be noted that several tantalum complexes have been prepared that contain a pentafluorophenyl-substituted or trimethylsilyl-substituted version of the [HNNNH] 3 ligand [16]. Other types of conformationally rigid multidentate amido ligands have appeared in the literature relatively recently [17 25]. It is interesting to note that cationic zirconium(IV) complexes containing the [(t-BuN-oC6H4)20]-' ligand [22] are catalysts for the living polymerization of 1-hexene at room temperature or below.
We expect that other examples of the utility of appropriately substituted multidentate amido ligands in high oxidation state chemistry, especially those that contain the o-phenylene backbone, will be forthcoming. EXPERIMENTAL
General details
Standard experimental procedures can be found elsewhere [1]. All N M R chemical shifts are reported in ppm downfield from TSM (~H and ~3C) external reference. Microanalyses (C, H, N) were performed in our laboratory using a Perkin-Elmer PE2400 microanalyzer. Cp*MoCI 4 [26], Cp*WC14 [15], 2,2'dinitrodiphenylamine [11], and 2-nitro-2'-hydroxydiphenylamine [12] were prepared as described in the literature. Preparation qlcompounds
Cp*Mo[HNNO]C1 (la). A yellow solution of 2amino-2'-hydroxy diphenylamine (0.537 g, 2.68 mmol) and Et3N (0.841 g, 8.31 mmol) in THF (10 ml) was added dropwise to a slurry of purple Cp*MoCI4 (1.00 g, 2.68 mmol) in 50 ml of THF at - 4 0 C. The solution color changed to red-brown and some solid precipitated. The mixture was warmed to room temperature, stirred for 22 h, and filtered. The solid was washed with THF until the washings were colorless. The solvents were removed from the red-brown filtrate and the brown residue was recrystallized from a small amount of dichloromethane to give almost black microcrystals; yield 0.810 g (65%): ESR (CHzC1,) 9 = 1.98 : AI~2 = 9.9 g. Anal. Calc. for Q,2H,4C1MoN20: C, 56.97: H, 5.22; N, 6.04; CI, 7.64. Found: C, 56.30: H, 5.19; N, 6.00: CI, 7.69. Cp*W[HNNO]C1 (lb). A yellow solution of 2amino-2'-hydroxy diphenylamine (1.91 g, 9.55 mmol) and NEt~ (3.00 g, 29.65 mmol) in THF (20 ml) was added to a red suspension of Cp*WCI~ (4.40 g, 9.55 mmol) in THF (100 ml) at - 4 0 C. The solution color changed gradually to green-brown as a white solid deposited. The mixture was warmed to room temperature and stirred for 42 h. The reaction mixture was filtered and the solid was washed with THF until the washings were colorless. The volatile solvents were removed from the green-brown filtrate in vacuo and the residue was washed with cold dichloromethane (4 x 5 ml) to give a green solid: yield 4.48 g (85%): ESR (CH2CI2),q = 1.93: Avl:~ = 18.5 g. Anal. Calc. for C=He4C1N2OW: C, 47.89; H, 4.38; N, 5.08. Found : C, 48.23 ; H, 4.44 ; N, 5.04. {Cp2Co}{Cp*Mo[HNNO]CI} (2). A solution of 40 mg (0.21 mmol) of cobaltocene in 5 ml ether was added dropwise to a red-brown solution of 0.100 g (0.21 mmol) Cp*Mo[HNNO]CI in 10 ml of THF. The color of the solution changed immediately to red.
Molybdenum and tungsten Cp* complexes After 24 h pentane was layered on top of the solution and the sample was kept at -30':C for 24 h to give brown microcrystals ; yield 0.120 g (0.18 mmol, 86% ) : IN NMR (THF-ds) 6 7.20-6.00 (m, 8, ArHL 3.95 (s, 10, Cp), 1.25 (s, 15, Cp*). The [HNNO] 3 ligand~s NH proton was not located. It is believed either to be in the region of 7.20-6.00 ppm or to be too broad at 22"C to be observed readily. Anal. Calc. For C3,H~4CICoMoN20: C, 58.86; H, 5.25; N, 4.29. Found : C, 58.87 : H, 5.44 : N, 4.08. {Na[O(C2Hs)2]Cp*Mo[HNNO]CII, (3). Sodium amalgam (1 equiv, of 0.05% Na/Hg) was added to a red brown solution of 200 mg (0.43 mmol) Cp*Mo[HNNO]CI in 10 ml of THF. The mixture was stirred until the color changed to orange (20-30 min). The mixture was filtered and the residue was washed with THF until the washings were colorless. The solvents were removed from the orange filtrate & t,acuo to give an orange glass. The orange glass was dissolved in a mixture of ether and pentane (1 : 1 ; 10 ml) and 10 ml of pentane was layered on top. Large brown crystals formed with time; yield 160 mg (0.33 mmol, 77%): IH NMR (THF-d~) 6 7.80 (br s, 1 N H ) , 6.89 6.55 (m, 8, ArH), 3.43 3.30 (q, 4, ether CH2), 1.141.03 (t, 6, ether CH3), 1.11 (s, 15 Cp*). Anal. Calc. for C,6H34CIMoN2NaO2 : C, 55.67 ; H, 6.11 : N, 4.99. Found: C, 55.42; H, 5.76; N, 5.32. {Cp*W[HNNO]C1}OTf (4). A solution of AgOTf (0.265 g, 1.03 mmol) in CH3CN (5 ml) was added dropwise to a green suspension of Cp*W[HNNO]C1 (0.570 g, 1.03 mmol) in CH3CN (10 ml). A gray solid formed immediately and the color of the solution changed to red. The mixture was stirred at room temperature for 4 h and filtered. The solvent was removed from the filtrate in z,acuo and the residue was extracted with dichloromethane. The red extract was reduced in volume and diethyl ether (15 ml) was layered on top. The mixture was cooled to - 3 0 C to produce redpurple crystals which were isolated by filtration and dried in eacuo : yield 0.662 g (91%) : 1H NMR (CDCI3 6 11.37 (s, 1, NH), 7.65-6.80 (4 doublets and 4 triplets, 8, ArH), 2.59 (s, 15, Cp*). Anal. Calc. for Cz3H24CIF3N~O4SW: C, 39.42; H, 3.45; N, 4.00. Found: C, 39.52 ; H, 3.75 : N, 3.85. Cp*Mo[HNNO](NH3) (5a). Hydrazine (28.9 ilk 0.91 mmol) was added to a red-brown solution of Cp*Mo[HNNO]C1 (0.210 g, 0.45 mmol) in THF (10 ml) at - 4 0 C . The mixture was allowed to warm to room temperature. Over a period of 22 h the color changed gradually to green and a white solid formed. The mixture was filtered and the solvent was removed from the filtrate in racuo. The residue was dissolved in ether (5 ml) and pentane was added just short of precipitating the product. Upon cooling this solution to - 4 0 : C , green crystals were formed and isolated by filtration; yield 0.188 g (93%): ~H NMR (THF-d,~, --88 C) 6 8.34 (br s, 1 NH), 7.90 6.66 (m, 8, ArH), 2.96 (br s, 3, NH~), 1.1 (s, 15, Cp*). Anal. Calc. for C22H27MoN30: C, 59.32; H, 6.11; N, 9.43. Found: C, 59.44; H, 5.84; N, 9.19.
755
Cp*W[HNNO](NH3) (5b). Hydrazine (73 /A, 2.29 mmol) was added to a green suspension of Cp*W [HNNO]CI (0.418 g, 0.76 mmol) in THF (20 ml). The mixture was stirred at room temperature for 72 h. The color gradually changed to green-brown and a white solid formed. The mixture was filtered and the filtrate was reduced in volume in vacuo. Pentane (20 ml) was added to precipitate the product ; yield 0.376 g (93%) : hH NMR (THF-d~, 23-C) 6 7.84-6.60 (m, 8, ArH), 1.17 (s, 15, Cp*): IH NMR (THF-ds, - 8 4 C ) 6 8.27 (br s, 1, NH), 7.85 6.58 (m, 8, ArH), 3.68 (br s, 3, NH3L 1.39 (s, 15, Cp*). Cp*W[HNNNH]CI (6). A solution of 2,2'-diaminodiphenylamine (2.86 g, 14.4 mmol) and triethylamine (4.50 g, 44.5 mmol) in THF (20 ml) was added dropwise to a red suspension of Cp*WC14 (6.62 g, 14.4 mmol) in THF (100 ml) at --40 C. The color changed to dark red immediately and a white solid gradually deposited. After the addition was completed, the mixture was warmed to room temperature and stirred for 22 h. The reaction mixture was filtered and the solid was washed with THF until the washings were almost colorless. All volatile components were removed from the filtrate in t,actto and the red residue was dissolved in a minimum amount of hot dichloromethane. The solution was cooled to - 4 0 'C to yield small red crystals, which were isolated by filtration and dried #l t,acuo; yield 5.98 g (76%): ESR (CH,C12),q = 1.94; Avl: = 20.0 g; IR (KBr, Nujol) cm ~ 3322 (VNH). Anal. Calc. for C2_,H2sC1N~W: C, 47.98 ; H, 4.58 ; N, 7.63. Found : C, 47.87 ; H, 4.70 : N, 7.89. [Cp*W[HNNNH]CI]OTf (7a). A solution of AgOTf (1.706 g, 6.64 mmol) in CH~CN (10 ml) was added dropwise to a red slurry of Cp*W[HNNNH]C1 (3.66 g, 6.64 mmol) in CH3CN (50 ml) at room temperature. Silver metal formed and the solution changed to red-brown. The mixture was stirred for 1 h and filtered and the solid was washed with CH3CN until the washings were colorless. The filtrate was reduced in volume (10 ml) and CH2CI: added to precipitate the product; yield 4.46 g (96%): ~H NMR (CD~CN) 6 10.23 (br s, 2, NH), 7.83 (d, 2, ArH), 7.28 (d, 2, ArH), 7.11 (t, 2, ArH), 6.90 (t, 2, ArH), 2.49 (s, 15, Cp*); IR (KBr, Nujol) cm i 3307 (vxlt). [Cp*W[HNNNH]CI}PF6 (7b). A solution of NOPF6 (0.284 g, 1.62 mmol) in CH3CN (5 ml) was added dropwise to a cold ( - 4 0 C ) suspension of Cp*W[HNNNH]C1 (0.894 g, 1.62 mmol) in CH3CN ( 10 ml). Gas evolved and the color changed to yellowbrown. The mixture was warmed to room temperature and stirred for another hour. Solvents were removed in t,acuo leaving a brown solid; yield 1.10 g (98%): ~H NMR (CD~CN) 6 10.22 (br s, 2, N H ) , 7.84 (d, 2, ArH), 7.27 (d, 2, ArH), 7.12 (t, 2, ArH), 6.90 (t, 2, ArH), 2.49 (s, 15, Cp*); IR (KBr, Nujol) cm ~ 3352 (v~H). Anal. Calc. for C22H2sCIF6N3PW: C, 37.98; H, 3.62; N, 6.04. Found: C, 37.76; H, 3.65; N, 6.10. Cp*W[HNNNH]01~-NNMe2) (Sa). 1,1-Dimethylhydrazine (38/~1, 0.51 retool) was added to a yellowbrown solution of [Cp*W[HNNNH]CII PF6 C0.116 g,
756
S. Cai et al.
0.17 mmol) in CH3CN (15 ml) at - 40"C. The solution changed to green, then a yellow precipitate formed. The mixture was allowed to warm to room temperature and was stirred for 30 rain. The reaction mixture was filtered and the yellow solid was washed with cold CH3CN (5 ml) and dried in vacuo: yield 0.035 g (37%): ~H N M R (C6D6) 6 8.11-6.90 (m, 8, ArH), 6.35 (s, 2, NH), 3.04 (s, 6, NNMe2), 1.50 (s, 15, Cp*); ~H N M R (CD2C12) 6 7.86 6.75 (m, 8, ArH), 6.69 (s, 2, NH), 3.63 (s, 6, NNMe2), 1.60 (s, 15, Cp*); ~3C{~H} NMR (CD2C12) 0 153.5 115.0 (6 singlets, ARC), 111.8 (s, CsMe5), 48.9 (s, NNMe2), 10.4 (s, CsMes). Anal. Calc. for C24H31N5W: C, 50.27; H, 5.45: N, 12.21. Found: C, 50.64; H, 5.22; N, 12.26. Cp*W[HNNNH](N-i-Pr) (Sb). A solution of iPrNH2 (0.49 ml, 5.75 mmol) in CH3CN (5 ml) was added dropwise to a brown solution of [Cp*W[HNNNH]CI}PF6 (1.00 g, 1.44 retool) in CH3CN (10 ml) at -40"C. The solution changed to red immediately and a red precipitate formed. The mixture was warmed to room temperature and stirred for 16 h. The mixture was then cooled to - 4 0 ° C and allowed to stand at this temperature for 12 h. The red solid was collected by filtration and washed with cold CH3CN (5 ml). It was then extracted with toluene until the extracts were colorless. Solvents were removed from the combined extracts to give the red product: yield 0.575 g (70%): ~H NMR (CD2CI2) 7.75 6.68 (m, 8, ArH), 6.49 (s, 2, NH), 5.63 (septet, 1, NCHMe2), 1.74 (s, 15, Cp*), 1.29 (d~ 6, NCHMe,). Anal. Calc. for C,sH32N4W: C~ 52.46; H, 5.63; N, 9.79. Found: C, 52.17; H, 5.83; N, 9.71. Cp*W[HNNNH](O) (9). This complex could be prepared either from {Cp*W[HNNNH]C1}PF6 or {Cp*W[HNNNH]CI}OTf. Degassed H20 (29/~1, 1.61 retool) was added to a mixture of {Cp*W [HNNNH]CIlOTf (0.750 g, 1.07 retool) and K2CO3 (0.760 g, 5.50 mmol) in CH3CN (20 ml) at 0'C. The mixture was stirred at 0':C for 2 h, then warmed to room temperature and stirred for another 18 h. The volatile components were removed in vacuo. The residue was extracted with dichloromethane until the extracts were colorless. Dichloromethane was removed from the combined extracts in vacuo and the brown crystalline solid was washed with CH3CN (2 x 5 ml) and dried in vacuo ; yield 0.555 g, 98%7 : IH N M R (CDCI3) 6 7.80-6.76 (m, 8, Ark/), 6.59 (s, 2, NH), 1.83 (s, 15, Cp*); 1R (KBr, Nujol) cm i 3376 and 3247 (VNH), 885 (Vwo). Anal. Calc. for C~2H25N3OW : C, 49.73 ; H, 4.74; N, 7.91. Found: C, 49.84 ; H, 5.07 : N, 7.87. Cp*W[HNNNH]Me (10). ZnMe2 (0.16 ml, 2.32 mmol) was added to a suspension of Cp*W [HNNNH]C1 (0.920 g, 1.67 mmol) in toluene (15 ml). The reaction flask was sealed with a septum and was heated at 80~C for l h. The solution changed to redpurple and a green solid deposited. The mixture was cooled to room temperature and filtered. The green solid was washed with toluene until the washings were almost colorless. The residue was extracted with
diethyl ether until the extracts were colorless. The combined ether extracts were chromatographed on a short alumina column using diethyl ether as eluent solvent. A red-purple band was collected. The volume of the solution was then reduced to ~ 3 ml 01 racuo. The solution was cooled to - 4 0 : C . The red-purple solid was collected by decanting the supernatant liquid and was dried in vacuo: yield 0.570 g (64%): ESR (CH2C12) 9 = 1.98; Av~2 = 17.3 g. Anal. Calc. for C~3H2~N3W: C, 52.09; H, 5.32; N, 7.92. Found: C, 52.39 ; H, 5.42 ; N, 7.89. {Cp*W[HNNNH]Me}OTf (11). M e t h o d A. A cold (-40'~'C) solution of Cp*W[HNNNH]Me (0.114 g, 0.21 mmol) in CH2C12 (5 ml) was added quickly to a suspension of triflic acid (19 pl, 0.21 mmol) in CH2C12 (10 ml) at -40"C. The mixture was slowly warmed to room temperature and stirred for 3 days. The solution gradually changed from red-purple to green and a small amount of white solid formed. The mixture was filtered through a frit and the green filtrate reduced in volume (3 ml). Diethyl ether (15 ml) was layered on top. Green crystals grew slowly at 2TC. The crystals were isolated by decanting the mother liquor; yield 95 mg (65%): ~H NMR (CD3CN) 6 9.80 (br s, 2, NH), 7.68 (d, 2, ArH), 7.07 (t, 2, ArHL 7.05 (d, 2, ArH), 6.85 (t, 2, ArH), 2.31 (s, 15, Cp*), 0.71 (s, 3, Me). Anal. Calc. for C24H28F3N303SW : C, 42.43 ; H, 4.15 ; N, 6.18. Found: C, 43.01 ; H, 4.26; N, 6.50. M e t h o d B. To a purple solution of Cp*W [HNNNH]Me (0.300 g, 0.57 retool) in THF (5 ml) was added dropwise a solution of AgOTf (0.145 g, 0.57 mmol) in THF (5 ml) at room temperature. A silver mirror formed immediately and a green solid deposited. Acetonitrile (10 ml) was added to the reaction mixture and the mixture was stirred for 30 min. The resulting mixture was filtered through a medium frit bedded with Celite. The green filtrate was reduced to ~ 3 ml b7 vacuo. Diethyl ether (15 ml) was layered on top. Green crystals formed with time at room temperature. The crystals were collected by decanting the supernatant liquid and dried hi t,acuo; yield 0.353 g (92%). Cp*W[(2-N-C6H4)(2'-NH-C6H4)N]Me (12). DBU (27.3 pl, 0.18 mmol) was added to a green slurry of {Cp*W[HNNNH]Me}OTf (0.124 g, 0.18 mmol) in CH.,CI2 (10 ml) at - 4 0 ' C . The color of the solution changed to red immediately. The mixture was warmed to room temperature and stirred for 1 h. All volatile components were removed in vacuo and the residue was extracted with diethyl ether until the extracts were colorless. The solvents were removed from the red extracts to give a red solid; yield 0.080 g (83%): IH N M R (CD2C12) 6 8.25 (br s, 1, NH), 7.54-6.26 (m, 8, ArH), 2.01 (s, 15, Cp*), 0.46 (s, 3, Me); IH NMR (CDCI3) 6 8.17 (br s, 1, NH), 7.61 6.30 (m, 8, ArH), 2.01 (s, 15, Cp*), 0.54 (s, 3, M e ) ; 13C{~H} NMR (CDC13) 6 158.8 114.6 (11 singlets, ARC), 113.6 (s, CsMe5), 18.4 (s, W M e ) , 11.2 (s, CsMes). Anal Calc. for C23H27N3W: C, 52.19; H, 5.14; N, 7.94. Found: C, 52.61 ; H, 5.30; N, 8.15.
Molybdenum and tungsten Cp* complexes
Crystal structure o[ {Na[O(C2Hs)2]Cp*Mo[HNNO]CI}2 (3). An orange-brown prismatic crystal of dimension 0.25 x 0.28 x 0.47 mm was mounted in a glass capillary in a nitrogen atmosphere. The data were collected at room temperature on a Rigaku diffractometer with a graphite-monochromated M o K~ radiation (2 = 0.71069 A). Of the 3276 reflections that were collected, 3131 were unique, and equivalent reflections were merged. The intensities of three representative reflections measured after every 150 reflections remained constant throughout data collectiom obtained from a least-squares refinement using the setting angles of 23 carefully centered reflections in the range 13.94: < 20 < 20.44 '~ corresponded to a monoclinic cell with the dimensions a = 15.367(4) A, b = 20.850(37 A, c = 12.271(2) /k and /~ = 113.71(3) for Z = 4. Based on systematic absences the space group was determined to be C_, (#5). The calculated density is 1.456 g/cm 3. A numerical absorption correction, using the program DIFABS, was applied, resulting in transmission factors ranging from 0.76 to 1.32. The structure was solved by Patterson's method. The final cycle of full matrix least-squares refinement was based on 1288 observed reflections (1 > 4a(I)) and 91 variable parameters and converged (largest parameter shift was 3.8 times its esd) with unweighted and weighted agreement factors of R = 0.082 and R, = 0.091. The maximum and minimum peaks on the final difference Fourier correspond to 1.13 and - 0 . 9 3 e-//k 3, respectively. All calculations were performed using the TEXAN crystallographic software package. Due to a disorder problem the pentamethylcyclopentadienyl ligand and all phenyl rings were refined as rigid groups. Crystal structure q/CCp*Mo[HNNO](NH3) (5a). A green prismatic crystal with dimensions 0.3 x 0.2 x 0.2 mm was mounted on a glass fiber under a stream of cold nitrogen gas from a liquid nitrogen bath. Data were collected at 72:C on an Enraf-Nonius CAD 4 diffractometer with a graphite-monochromated M o K~ radiation (2 = 0.71069/~). Of the 8525 reflections that were collected, 4146 were unique, and equivalent reflections were merged. The intensities of three representative reflections measured after every 60 min remained constant throughout data collection, obtained from a least-squares refinement using the setting angles of 25 carefully centered reflections in the range 18.00: < 20 < 26.00 :~ corresponded to a tetragonal cell with the dimensions a = 19.105(2) A and c = 12.271(2) A for Z = 8. Based on systematic absences the space group was determined to be P4,.n (#86). The calculated density is 1.322 g/cm 3. An empirical absorption correction, based on azimuthal scans of five reflections, was applied, resulting in transmission factors ranging from 0.95 to 1.00. The structure was solved by Patterson's method. The final cycle of full matrix least-squares refinement was based on 2044 observed reflections (I > 4a(/)) and 252 variable parameters and converged (largest parameter shift was 0.00 times its esd) with unweighted and weighted
757
agreement factors of R = 0.045 and R,. = 0.037. The maximum and minimum peaks on the final difference Fourier correspond to 0.47 and - 0 . 6 9 e - / A 3, respectively. All calculations were performed using the TEXAN crystallographic software package. Supplementary information covering experimental details, labelled ORTEP drawing, final positional parameters, final thermal parameters, and final observed and calculated structure factors for [NaO(C_,Hs), Cp*Mo[(2-NH-C6H4)(2'-O-C6H4)N]C1}2 (16 pp) and Cp*Mo[(2-NH-C6H4)(2'-O-C,,H4)N](NH3) (20 pp) is available upon request.
Acknowledgements--R.R.S. thanks the National Institutes of Health for support (GM 341978) and R.R.K. thanks the German AcademicExchange Servicefor a HEP postdoctoral fellowship.
REFERENCES
1. Glassman, T. E., Vale, M. G., Schrock, R. R. and Kol, M., J. Am. Chem. Soc., 1993, 115, 1760. 2. Glassman, T. E., Vale, M. G. and Schrock, R. R., J. Am. Chem. Soc., 1992, 114, 8098. 3. Glassman, T. E., Vale, M. G. and Schrock, R. R., Organometallics, 1991, 10, 4046. 4. Glassman, T. E., Liu, A. H. and Schrock, R. R., lnor.q. Chem., 1991, 30, 4723. 5. O'Regan, M. B., Liu, A. H., Finch, W. C., Schrock, R. R. and Davis, W. M., J. Am. Chem. Soc., 1990, 112, 4331. 6. Schrock, R. R., Glassman, T. E. and Vale, M. G., J. Am. Chem. Soc., 1991, 113, 725. 7. Schrock, R. R., Kolodziej, R. M., Liu, A. H., Davis, W. M. and Vale, M. G., J. Am. Ctwm. Soc., 1990, 112, 4338. 8. Vale, M. G. and Schrock, R. R., Organometallics, 1993, 12, 1140. 9. Hidai, M. and Mizobe, Y., Chem. Rev., 1995, 95, 1115. 10. O'Regan, M. B., Vale, M. G., Payack, J. F. and Schrock, R. R. hmr#. Chem., 1992, 31, 1112. 11. Tomlinson, M. L., J. Chem. Soc., 1939, 158. 12. Wilshire, J. F. K. Aust. J. Chem., 1988, 41,995. 13. Kubacek, P., Hoffmann, R. and Havlas, Z. Or,qanometallics, 1982, 1,180. 14. Sundermeyer, J., Radius, U. and Burschka, C. Chem. Bet'., 1992, 125, 2379. 15. Liu, A. H., Murray, R. C., Dewan, J. C., Santarsiero, B. D. and Schrock, R. R., J. Am. Chem. Sot., 1987, 109, 4282. 16. Schrock, R. R., Lee, J., Liang, L.-C. and Davis, W. M., Inor9. Chhn. Acta, in press. 17. Guerin, F., McConville, D. H. and Vittal, J. J., Organometallics, 1995, 14, 3154. 18. Gu6rin, F., McConville, D. H. and Vittal, J. J., Organometallics, 1996, 15, 5586. 19. Gu6rin, F., McConville, D. H. and Payne, N. C. Organometallics, 1996, 15, 5085. 20. Guarin, F., McConville, D. H. and Vittal, J. J., Organometallics, 1997, 16, 1491.
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21. Fryzuk, M. D., Love, J. B., Rettig, S. J. and Young, V. G., Science, 1977, 275, 1445. 22. Baumann, R., Davis, W. M. and Schrock, R. R., J. Am. Chem. Soc., 1997, 119, 3830. 23. Cloke, F. G. N., Hitchcock, P. B. and Love, J. B., J. Chem. Sot., Dalton Trans., 1995, 25. 24. Horton, A. D., de With, J., van der Linden, A. J.
and van de Weg, H., Organometallics, 1996, lfi, 2672. 25. Clark, H. C. S., Cloke, F. G. N., Hitchcock, P. B., Love, J. B. and Wainwright, A. P., J. Organometal. Chem., 1995, fi01, 333. 26. Murray, R. C., Blum, L., Liu, A. H. and Schrock, R. R., Organometallics, 1985, 4, 954.
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Pergamon PII : S0277-5387(97)00394-X
',c 1998 Elsevier Science Ltd All rights reserved. Printed in Great Britain 0277 5387/98 $19.00+0.00
Molybdenum and tungsten Cp* complexes that contain 2,2'-diamidodiphenylamido or 2amido-2'-oxydiphenylamido ligands Shi'ang Cai, Richard R. Schrock,* Rhett R. Kempe and W. M. Davis Department of Chemistry 6-331, Massachusetts Institute of Technology Cambridge, MA 02139, U.S.A.
(Received 25 April 1997; accepted 1 August 1997)
Abstract Cp*MC14
compounds (M = Mo or W) react with 2-amino-2'-hydroxydiphenylamine ([H2NNHOH]) to yield complexes of the type Cp*M[HNNO]CI. An X-ray study of the one electron reduction product, {Na(C2Hs)20}{Cp*Mo[HNNO]C1}, showed it to contain square pyramidal {Cp*Mo[HNNO]C1] ions weakly connected by bridging Na(ether) units. Cp* W[HNNO]C1 could be oxidized readily by AgOTf in acetonitrile to produce {Cp*W[HNNO]C1} +OTf . Both Cp*M[HNNO]CI compounds are reduced by hydrazinc to give the diamagnetic compound, Cp*M[HNNO](NH3). An X-ray structure of Cp*Mo[HNNO](NH3) showed that the almost planar [HNNO] 3 ligand and the ammonia ligand occupy the four basal positions in an approximately square pyramidal "piano stool" complex. Red crystalline Cp*W[HNNNH]CI ([HNNNH] 3 = [(2-NHC6H4)2N] 3-) could be prepared from Cp*WC14 and 2,2'-diaminodiphenylamine. It can be oxidized with AgOTf or NOPF6 to yield {Cp*W[HNNNH]CI}X (X = OTf or PF0. {Cp*W[HNNNH]CI]PF6 reacts with three equivalents of NH2NMe2 to afford Cp*W[HNNNH](NNMe2), with four equivalents of isopropylamine to produce Cp*W[HNNNH](N-i-Pr), and with water in the presence of K2CO3 to yield Cp*W[HNNNH](O). Cp*W[(HNNNH]CI reacts with dimethyl zinc at 80 '= to give Cp*W[HNNNH]Me, which can be subsequently oxidized by silver triflate to give {Cp*W[HNNNH]Me}OTf. Deprotonation of {Cp*W[HNNNH]Me}OTf with DBU yielded an imido complex, Cp*W[(2-N-C6H4)(2'-NHC6H4)N]Me via loss of one of the two ligand NH protons. '.f211998 Elsevier Science Ltd. All rights reserved
Keywords: molybdenum : tungsten ; 2,2'-diamidodiphenylamido; 2-amido-2'-oxydiphenylamido.
In the past few years we have synthesized and explored the chemistry of relatively high oxidation state tungsten or molybdenum complexes that will activate and reduce dinitrogen. In a series of studies we focused on complexes that contain the Cp*MMe~ core (M = W [1 5], Mo [3,6,7], or Re[8]). Some of the results that have emerged from these studies are as follows: (i) metals in a relatively high oxidation state (e.g. W(III) or W(IV)) can bind N2 or partially reduce (N2Hx) ligands ; (ii) a 2~, 1a arrangement of orbitals in such circumstances is favorable for stabilizing N2Hx ligands; and (iii) a complex that contains bound hydrazine is a likely intermediate in which the N - - N bond is cleaved to give ammonia. Recent investigations of the chemistry of tungsten and molybdenum phosphine complexes that is relevant to dinitrogen fixation has also begun to focus on the
* A u t h o r to w h o m c o r r e s p o n d e n c e s h o u l d be a d d r e s s e d .
"mid" oxidation states for binding partially reduced (N2H0 ligands [9]. Unfortunately, there is at least one significant disadvantage to complexes that contain the Cp*MMe3 core. If we are to have any hope of reaching our longterm goal of developing a catalytic system for the reduction of dinitrogen using protons and electrons, methyl ligands eventually are protonated and lost as methane. Complexes that contain monodentate alkoxide ligands [10] did not prove to be suitable, in part because alkoxides also are readily protonated and can undergo ligand redistribution reactions that significantly complicate the chemistry in which we are interested. Therefore we looked for multidentate trianionic ligands that could take the place of the three methyl groups in the Cp*MMe3 core and that would be less susceptible than methyl ligands toward protonation and subsequent dissociation from the metal. 2,2'-Diaminodiphenylamine [11] and 2-amino-2'hydroxydiphenylamine can be prepared by reducing
749
750
S. Cai et al.
the corresponding nitro compounds [12]. We felt that trianions derived from such compounds, [HNNNH] 3or [HNNO] 3 (see below), would bind to Mo or W to yield complexes that contain Cp*M(HNNNH) or Cp*M(HNNO) cores. The o-phenylene rings should enforce planarity of the ligand system and therefore should encourage formation of pseudo five-coordinate complexes having a "piano stool" geometry. They also should discourage protonation of the amido nitrogen atoms. In this paper we report the synthesis of MCp*[HNNO] (M = Mo or W) and WCp*[HNNNH] complexes, X-ray structures of two MoCp*[HNNO] derivatives, and some chemistry that suggests that such ligands may prove useful for high oxidation state Mo or W chemistry.
N/
-N
N/
\
H
H
-O
H
[HNNO]3-
[HNNNH] 3-
RESULTS AND DISCUSSION Complexes contain&9 (M = Mo, W)
the
Cp*M[HNNO]
Core
Cp*MoC14 reacts with 2-amino-2'-hydroxydiphenylamine in the presence of three equivalents of triethylamine to yield the 2-amido-2'-oxydiphenylamido ([HNNO] 3 ) derivative la [eqn (1)] as brown-black microcrystals in 65% isolated yield. An analogous reaction starting with Cp*WC14 yielded Cp*W[HNNO]C1 (lb). Both la and lh show ESR signals at g ~ 2, consistent with the presence of one unpaired electron. Although resonance forms can be drawn in which the metal is in a more reduced state, we prefer to view these as d ~M(V) complexes.
Cp*MCI4 + NH 2
HO H
+ 3 Et3N
~
- 3Et3HC1 '~
~
Cp*
(1)
!
'"'" IVI'"'
CI
d ~
M:Mo (la); W (1 b).
Reaction of la with CpzCo yields a diamagnetic species that we formulate as the d 2 complex, {Cp2Co}{Cp*Mo[HNNO]CI} (2) formed by one elec-
tron reduction of la (Scheme 1). Reduction of la with sodium amalgam in THF yields an analogous species (3) that is isolated as a sodium salt containing one equivalent of diethyl ether. The proton on nitrogen in the HNNO ligand could be observed at 7.80 ppm in the proton NMR spectrum of 3 as a broad singlet, but not in 2 (at 22':C), perhaps because in 2 the NH proton cannot be differentiated from aryl protons between 7.20 and 6.00 ppm. An X-ray study of 3 showed it to contain approximately square pyramidal {Cp*Mo[HNNO]CI} ions weakly connected by bridging Na(ether) units (Fig. 1, Table 1) in a manner such that the O(2)--Na(I)--Na(2)--O(3) axis serves as a C: axis. The [HNNO] 3 ligand is approximately planar. Unfortunately, the structure had to be refined with the Cp* and phenyl rings as rigid groups, and therefore the quality is not high. The Na--C1 bond lengths are ~2.70 A, but the Na(1)--N(2) distance (2.55 A) and Na(2)--O(1) distance (2.51 A) suggest that these interactions are significant and that the sodium ions therefore are pseudo five-coordinate. The core bond lengths and angles in the {Cp*Mo [HNNO]CI}- ion are shown in Fig. 2 in order to illustrate that the approximately square pyramidal MoN2OCI core geometry is roughly the same as that found for a more accurately determined structure discussed below. Reduction of lb proceeds similarly to yield what appears, by proton NMR, to be the tungsten analog of 2, but this compound was not characterized further. Cp*W[HNNO]C1 could be oxidized readily by AgOTf in acetonitrile to produce {Cp*W[HNNO] CI} + OTf (4) essentially quantitatively. The NH proton in 4 was located at 11.37 ppm in the proton NMR spectrum. We assume that there is no room for the triflate ion to bind strongly to the metal and therefore have formulated 4 as an ionic species. In contrast, la was not oxidized under similar conditions to an analogous Mo(VI) species. Compounds la and lb are both reduced by hydrazine (2 equiv.) to give diamagnetic compounds with the formula Cp*M[HNNO](NH3) (5a and 5b, respectively). The only other observable product of these high yield reactions was N,H~ (according to N M R spectra), presumably as the chloride salt. The proton on nitrogen in the HNNO ligand and the ammonia protons could not be observed readily in either 5a or 5b as a consequence of facile proton exchange between these sites at room temperature. At low temperature the rate of the exchange process is slow enough that the HNNO proton can be observed near 8 ppm (8.34 ppm in 5a: 8.27 ppm in 5b) and the NH3 proton around 3 ppm (2.96 ppm in 5a ; 3.68 ppm in 5b). 5a is also formed upon addition of excess hydrazine to 3. We speculate that the mode of formation of compounds 5a and 5b from la and lb involves formation and decomposition of intermediate hydrazido(1-) species, Cp*M[HNNO](N2H3), as shown in eqns (2) and (3). This proposal is based on the fact that the W(V) complex, Cp*WMe3(N,H0, which is pro-
751
Molybdenum and tungsten Cp* complexes Cp*
I
HN .......... Mo ~ CI [CoCp2]
N
[NaO(C2Hs)2Cp*M°[HNNO]CI }2 (3)
~
a (Hg) ~ + CoCp2
+ excess N2H 4
2
/''(p*
HN ........... M
CI
N AgOTf "x,• "~
+ 2 N2H4/
- NzHsC1 Cp*
I
HN ...........M ~
/x
la (M = Mo) lb (M = W)
"AgO
Cp*
NH3
o
5a (M = Mo) 5b (M = W)
Scheme, I.
2.51
it
Na( 1)
Fig. 1. Molecular structure of {Na[O(C~H~)z]Cp*Mo[(2-NH-CoH4I(2"-O-C6H4)N]CI}2 (3). Hydrogen aloms are omitted for clarity,
posed to be formed upon deprotonation of [Cp*WMe3(NeH4)] +, decomposes to yield 0.5 equiv, of Cp*Me~W---NNH2, 0.5 equiv, of C p * M % W
= N H , and 0.5 equiv, of NH~ [1]. Since the proposed C p * M [ H N N O ] ( N 2 H 0 compounds would also contain the metal in the M(V) oxidation state, we propose
S. Cai et al.
752
Table 1. Selected bond lengths (A) and bond angles (:) in INa[O(C:Hs)2]Cp*Mo[HNNO]C1)_~ (3)
Table 2. Selected bond lengths (A) and bond angles ( ) in Cp*Mo[HNNO](NH0 (5a)
Mo--O(1) Mo--N(2) Na(I)--CI Na(I)--N(2) Na(1)--O(2)
2.13(2) 1.94(2) 2.70(2) 2.55(2) 2.20(4)
Mo--N(I) Mo--C1 Na(2)--CI Na(2)--O(l) Na(2)--O(3)
Mo--O(l) Mo--N(2) Mo--C(13) Mo--C(17) Mo--2(21)
O(I)--Mo--N(I) N(I)--Mo--N(2) N(2)--Mo--CI Na(1)--C1--Na(2)
73(1) 81(1) 80.6(6) 85.1(4)
O(I)--Mo--CI 84.9(5) O(1)--Mo--N(I) 77.0(2) N(I)--Mo--CI 131.1(4) N(I)--Mo--N(3) 87.9(2) N(2)--Mo--O(I} 128.7(9) N(3)--Mo--O(I) 126.0(2) CI--Na(1 )--CI' 95.4(7)
2.01(1) 2.510(4) 2.72(2) 2.51(2) 2.36(3)
that they also are likely to be unstable with respect to an intermolecular decomposition reaction shown in eqn (3). However, details of the decomposition reaction are unclear at this stage. It is also not clear why M(IV) ammonia complexes are formed rather than M = NNH2 or M = NH species. Cp* M[HNNO]CI + 2N2H4
N2HsCI+"Cp*M[HNNO](N2H3)'"
(2)
"Cp*M[HNNO](N2H3)'" Cp*M[HNNO](NH3) + 0.5N2
(3)
Crystals of 5a suitable for X-ray studies were obtained by recrystallization from an ether solution layered with pentane. The core structure of 5a (Fig. 3) is similar to that found in 3 (Fig. 2). Relevant bond lengths and angles are listed in Table 2 and the core of 5a is compared to that of 3 in Fig. 2. The 2-amidophenyl-2'-oxydiphenylamido ligand and the ammonia ligand occupy the four basal positions in a square pyramidal or "piano stool" arrangement typically found for pseudo-five-coordinate monocylopentadienyl complexes [13]. The [HNNO] 3 ligand is close to being planar and the two M o - - N and one M o - - O bonds are all essentially the same length and relatively short (2.02 to 2.05 /k). The N(3)--Mo--N(2) and N ( 2 ) - - M o - - O ( I ) bond angles are essentially equal, but the N(3)--Mo--N(1) bond
73o
2.049(5) 2.024(6) 2.238(7) 2.435(7) 2.208(7)
Mo--N(I) Mo--NI3) Mo--C(15) Mo--C(19)
O(1)--Mo--N(2) 77.1(2) N(2)--Mo--N(3) 75.3(2) N(2)--Mo--N(1) 131.3(2)
angle is larger than the O ( 1 ) - - M o - - N ( I ) bond angle by ~ 10~:, perhaps because of steric repulsion between the proton on N(3) and the protons on ammonia. The Mo--N(1) distance (2.225(6) A) is what one might expect for a dative M o - - N bond. The Cp* ligand is coordinated in an acentric fashion, with the Mo--C(17) distance being statistically longer that the other M o - - C distances. This circumstance is not unusual [14] and probably can be ascribed to greater repulsive forces between the ammonia ligand and the Cp* ligand compared to those between the flat HNNO ligand and the Cp* ligand. The protons on the ammonia ligand were not located in the X-ray study.
Synthesis and reactA, iO' o/ complexes containing the Cp*W[(2-NH-C6H4)_~N] core Cp*W[HNNNH]C1 (6; Scheme 2 ; [HNNNH] 3 = [(2-NHC6H4)2N]3 ) could be prepared from Cp*WCl4 and 2,2'-diaminodiphenylaminein the presence of at least three equivalents of triethylamine. Compound 6 is a red crystalline solid that is relatively soluble in CH2C12 and THF, but sparingly soluble in CH3CN and hydrocarbons. It can be stored in air over a period of several weeks without significant decomposition. It does not react with water or methanol in the presence of triethylamine, nor does it react readily with NH3 or N_~H+ Compound 6 was not reduced by cobaltocene or zinc amalgam. It did react with excess sodium
8,°
3
C1
2.226(6) 2.017(6) 2.356(7) 2.296(7)
5a
N
O-Mo-N =129°;N-Mo-C1= 131° O-Mo-N =126°; N-Mo-N= 131° Fig. 2. A comparison of bond lengths and angles in 3 and 5a.
Molybdenum and tungsten Cp* complexes
753
C(~7)
N(I) Fig. 3. Molecular structure of Cp*Mo[(2-NH-C~HD(Y-O-C~HDN](NH3) (Sa). Hydrogen atoms are omitted for clarity.
Cp*
Cp* 1 ]+ + H2NNMe2 HN ........W - - CI/ X " ~ HN
AgOTf HN
........
W ~ CI
Cp*
I
........
W - - - NNMe2
or NOPF6
6 7a (X = OTf)
~ +Zn(CH3)2
7b (X = PFs)
N ~ + H2NCHMe2
\
K2CO3 ~ H20 Cp*
Cp*
f
1
HN ........W ~
CH3
HN ........W --- NCHMe2
9
8b
+ AgOTf or HOTf
Cp*
i
I
HN ........W ---" O
10
~
Cp*
Cp*
+ DBU
N~
4
l
W~CH 3
+ HOTf 11
12 Scheme. 2.
amalgam in T H F to produce an extremely air-sensitive diamagnetic species in low yield (30% from acetonitrile), but this product was not characterized. C o m p o u n d 6 can be oxidized readily, For example, it reacts cleanly with A g O T f or NOPF~ to afford {Cp*W[HNNNH]C1}X (X = OTf, 7a ; PF~, 7b) quantitatively, Both compounds are soluble in acetonitrile, but insoluble in other c o m m o n organic solvents. 'H N M R spectra of the two in CD3CN are ahnost identical, consistent with their proposed ionic nature. The [ H N N N H ] 3- ligand N H resonance is found as a broad
singlet at 10.22 ppm in the proton N M R spectrum in CD~CN. Compound 7b reacts with three equivalents of N H z N M e : to afford C p * W [ H N N N H ] ( N N M e 2) (Sa) in moderate (37% isolated) yield. C o m p o u n d 7b also reacts with four equivalents of isopropylamine to produce Cp*W[HNNNH](N-i-Pr) (8b), and with water in the presence of KzCO3 to yield C p * W [ H N N N H ] ( O ) (9). Proton N M R spectra of 8 and 9 in C~D6 reveal the [ H N N N H ] 3- ligand N H resonance at ~6.5 ppm. Compound 6 reacts with dimethyl zinc slowly at
754
S. Cai et al.
room temperature, and at 80': Cp*W[HNNNH]Me (10) is formed in good yield (67% isolated) in 1 h. Compound 10 is oxidized quantitatively by silver triflate to give {Cp*W[HNNNH]MelOTf (11). Interestingly, an attempt to protonate 10 with one equivalent of triflic acid in CH2C12 led (slowly over a period of 3 days) to its oxidation to give 11 in moderate yield (65% isolated). The proton NMR spectrum of 11 in CD3CN showed a resonance at 0.71 ppm, for the methyl group. Only four different aromatic protons were observed, consistent with the molecule having mirror symmetry. Compound 11 is a rare example of a cationic W(VI) alkyl complex (cf. [Cp*WMes]+). [15]. Deprotonation of 11 with DBU did not give Cp*W[HNNNH](CH2), but an imido complex, Cp*W[(2-N-C6H4)(2'-NH-C6H4)N]Me (12), formed via loss of one of the two ligand NH protons. The NMR spectrum of 12 is relatively complex, as expected for a molecule having no symmetry. Normally eight proton resonances are observed in the aromatic region, but if 12 is contaminated with a trace of a proton source, even DBUHOTf, only four different aromatic proton resonances are observed, consistent with protonation and deprotonation of 12 being a fast and reversible process. Addition of one equivalent of HOTf to 12 yields 11 quantitatively. Formation of 12 should be compared to deprotonation of [Cp*WMes] + to yield unstable Cp*WMe3(CH2) [15].
CONCLUSIONS Multidentate amido ligands that contain o-phenylene links between amido nitrogens show some promise as supporting ligands for high oxidation state Cp*Mo or Cp*W chemistry. Among the interesting features of complexes that contain such ligands are the planar tridentate ligand backbone, the stability of the backbone to proton abstraction and cleavage reactions, and the ability of several complexes to be smoothly oxidized or reduced. For steric reasons, the parent (proton-substituted) versions of the two ligands described here are likely to be the only ones that can be put on Cp*M complexes to give approximately square pyramidal complexes. Conversely, more steric protection against bimolecular reactions is likely to be required if multidentate amido ligands are employed in the absence of other bulky ligands. In this context it should be noted that several tantalum complexes have been prepared that contain a pentafluorophenyl-substituted or trimethylsilyl-substituted version of the [HNNNH] 3 ligand [16]. Other types of conformationally rigid multidentate amido ligands have appeared in the literature relatively recently [17 25]. It is interesting to note that cationic zirconium(IV) complexes containing the [(t-BuN-oC6H4)20]-' ligand [22] are catalysts for the living polymerization of 1-hexene at room temperature or below.
We expect that other examples of the utility of appropriately substituted multidentate amido ligands in high oxidation state chemistry, especially those that contain the o-phenylene backbone, will be forthcoming. EXPERIMENTAL
General details
Standard experimental procedures can be found elsewhere [1]. All N M R chemical shifts are reported in ppm downfield from TSM (~H and ~3C) external reference. Microanalyses (C, H, N) were performed in our laboratory using a Perkin-Elmer PE2400 microanalyzer. Cp*MoCI 4 [26], Cp*WC14 [15], 2,2'dinitrodiphenylamine [11], and 2-nitro-2'-hydroxydiphenylamine [12] were prepared as described in the literature. Preparation qlcompounds
Cp*Mo[HNNO]C1 (la). A yellow solution of 2amino-2'-hydroxy diphenylamine (0.537 g, 2.68 mmol) and Et3N (0.841 g, 8.31 mmol) in THF (10 ml) was added dropwise to a slurry of purple Cp*MoCI4 (1.00 g, 2.68 mmol) in 50 ml of THF at - 4 0 C. The solution color changed to red-brown and some solid precipitated. The mixture was warmed to room temperature, stirred for 22 h, and filtered. The solid was washed with THF until the washings were colorless. The solvents were removed from the red-brown filtrate and the brown residue was recrystallized from a small amount of dichloromethane to give almost black microcrystals; yield 0.810 g (65%): ESR (CHzC1,) 9 = 1.98 : AI~2 = 9.9 g. Anal. Calc. for Q,2H,4C1MoN20: C, 56.97: H, 5.22; N, 6.04; CI, 7.64. Found: C, 56.30: H, 5.19; N, 6.00: CI, 7.69. Cp*W[HNNO]C1 (lb). A yellow solution of 2amino-2'-hydroxy diphenylamine (1.91 g, 9.55 mmol) and NEt~ (3.00 g, 29.65 mmol) in THF (20 ml) was added to a red suspension of Cp*WCI~ (4.40 g, 9.55 mmol) in THF (100 ml) at - 4 0 C. The solution color changed gradually to green-brown as a white solid deposited. The mixture was warmed to room temperature and stirred for 42 h. The reaction mixture was filtered and the solid was washed with THF until the washings were colorless. The volatile solvents were removed from the green-brown filtrate in vacuo and the residue was washed with cold dichloromethane (4 x 5 ml) to give a green solid: yield 4.48 g (85%): ESR (CH2CI2),q = 1.93: Avl:~ = 18.5 g. Anal. Calc. for C=He4C1N2OW: C, 47.89; H, 4.38; N, 5.08. Found : C, 48.23 ; H, 4.44 ; N, 5.04. {Cp2Co}{Cp*Mo[HNNO]CI} (2). A solution of 40 mg (0.21 mmol) of cobaltocene in 5 ml ether was added dropwise to a red-brown solution of 0.100 g (0.21 mmol) Cp*Mo[HNNO]CI in 10 ml of THF. The color of the solution changed immediately to red.
Molybdenum and tungsten Cp* complexes After 24 h pentane was layered on top of the solution and the sample was kept at -30':C for 24 h to give brown microcrystals ; yield 0.120 g (0.18 mmol, 86% ) : IN NMR (THF-ds) 6 7.20-6.00 (m, 8, ArHL 3.95 (s, 10, Cp), 1.25 (s, 15, Cp*). The [HNNO] 3 ligand~s NH proton was not located. It is believed either to be in the region of 7.20-6.00 ppm or to be too broad at 22"C to be observed readily. Anal. Calc. For C3,H~4CICoMoN20: C, 58.86; H, 5.25; N, 4.29. Found : C, 58.87 : H, 5.44 : N, 4.08. {Na[O(C2Hs)2]Cp*Mo[HNNO]CII, (3). Sodium amalgam (1 equiv, of 0.05% Na/Hg) was added to a red brown solution of 200 mg (0.43 mmol) Cp*Mo[HNNO]CI in 10 ml of THF. The mixture was stirred until the color changed to orange (20-30 min). The mixture was filtered and the residue was washed with THF until the washings were colorless. The solvents were removed from the orange filtrate & t,acuo to give an orange glass. The orange glass was dissolved in a mixture of ether and pentane (1 : 1 ; 10 ml) and 10 ml of pentane was layered on top. Large brown crystals formed with time; yield 160 mg (0.33 mmol, 77%): IH NMR (THF-d~) 6 7.80 (br s, 1 N H ) , 6.89 6.55 (m, 8, ArH), 3.43 3.30 (q, 4, ether CH2), 1.141.03 (t, 6, ether CH3), 1.11 (s, 15 Cp*). Anal. Calc. for C,6H34CIMoN2NaO2 : C, 55.67 ; H, 6.11 : N, 4.99. Found: C, 55.42; H, 5.76; N, 5.32. {Cp*W[HNNO]C1}OTf (4). A solution of AgOTf (0.265 g, 1.03 mmol) in CH3CN (5 ml) was added dropwise to a green suspension of Cp*W[HNNO]C1 (0.570 g, 1.03 mmol) in CH3CN (10 ml). A gray solid formed immediately and the color of the solution changed to red. The mixture was stirred at room temperature for 4 h and filtered. The solvent was removed from the filtrate in z,acuo and the residue was extracted with dichloromethane. The red extract was reduced in volume and diethyl ether (15 ml) was layered on top. The mixture was cooled to - 3 0 C to produce redpurple crystals which were isolated by filtration and dried in eacuo : yield 0.662 g (91%) : 1H NMR (CDCI3 6 11.37 (s, 1, NH), 7.65-6.80 (4 doublets and 4 triplets, 8, ArH), 2.59 (s, 15, Cp*). Anal. Calc. for Cz3H24CIF3N~O4SW: C, 39.42; H, 3.45; N, 4.00. Found: C, 39.52 ; H, 3.75 : N, 3.85. Cp*Mo[HNNO](NH3) (5a). Hydrazine (28.9 ilk 0.91 mmol) was added to a red-brown solution of Cp*Mo[HNNO]C1 (0.210 g, 0.45 mmol) in THF (10 ml) at - 4 0 C . The mixture was allowed to warm to room temperature. Over a period of 22 h the color changed gradually to green and a white solid formed. The mixture was filtered and the solvent was removed from the filtrate in racuo. The residue was dissolved in ether (5 ml) and pentane was added just short of precipitating the product. Upon cooling this solution to - 4 0 : C , green crystals were formed and isolated by filtration; yield 0.188 g (93%): ~H NMR (THF-d,~, --88 C) 6 8.34 (br s, 1 NH), 7.90 6.66 (m, 8, ArH), 2.96 (br s, 3, NH~), 1.1 (s, 15, Cp*). Anal. Calc. for C22H27MoN30: C, 59.32; H, 6.11; N, 9.43. Found: C, 59.44; H, 5.84; N, 9.19.
755
Cp*W[HNNO](NH3) (5b). Hydrazine (73 /A, 2.29 mmol) was added to a green suspension of Cp*W [HNNO]CI (0.418 g, 0.76 mmol) in THF (20 ml). The mixture was stirred at room temperature for 72 h. The color gradually changed to green-brown and a white solid formed. The mixture was filtered and the filtrate was reduced in volume in vacuo. Pentane (20 ml) was added to precipitate the product ; yield 0.376 g (93%) : hH NMR (THF-d~, 23-C) 6 7.84-6.60 (m, 8, ArH), 1.17 (s, 15, Cp*): IH NMR (THF-ds, - 8 4 C ) 6 8.27 (br s, 1, NH), 7.85 6.58 (m, 8, ArH), 3.68 (br s, 3, NH3L 1.39 (s, 15, Cp*). Cp*W[HNNNH]CI (6). A solution of 2,2'-diaminodiphenylamine (2.86 g, 14.4 mmol) and triethylamine (4.50 g, 44.5 mmol) in THF (20 ml) was added dropwise to a red suspension of Cp*WC14 (6.62 g, 14.4 mmol) in THF (100 ml) at --40 C. The color changed to dark red immediately and a white solid gradually deposited. After the addition was completed, the mixture was warmed to room temperature and stirred for 22 h. The reaction mixture was filtered and the solid was washed with THF until the washings were almost colorless. All volatile components were removed from the filtrate in t,actto and the red residue was dissolved in a minimum amount of hot dichloromethane. The solution was cooled to - 4 0 'C to yield small red crystals, which were isolated by filtration and dried #l t,acuo; yield 5.98 g (76%): ESR (CH,C12),q = 1.94; Avl: = 20.0 g; IR (KBr, Nujol) cm ~ 3322 (VNH). Anal. Calc. for C2_,H2sC1N~W: C, 47.98 ; H, 4.58 ; N, 7.63. Found : C, 47.87 ; H, 4.70 : N, 7.89. [Cp*W[HNNNH]CI]OTf (7a). A solution of AgOTf (1.706 g, 6.64 mmol) in CH~CN (10 ml) was added dropwise to a red slurry of Cp*W[HNNNH]C1 (3.66 g, 6.64 mmol) in CH3CN (50 ml) at room temperature. Silver metal formed and the solution changed to red-brown. The mixture was stirred for 1 h and filtered and the solid was washed with CH3CN until the washings were colorless. The filtrate was reduced in volume (10 ml) and CH2CI: added to precipitate the product; yield 4.46 g (96%): ~H NMR (CD~CN) 6 10.23 (br s, 2, NH), 7.83 (d, 2, ArH), 7.28 (d, 2, ArH), 7.11 (t, 2, ArH), 6.90 (t, 2, ArH), 2.49 (s, 15, Cp*); IR (KBr, Nujol) cm i 3307 (vxlt). [Cp*W[HNNNH]CI}PF6 (7b). A solution of NOPF6 (0.284 g, 1.62 mmol) in CH3CN (5 ml) was added dropwise to a cold ( - 4 0 C ) suspension of Cp*W[HNNNH]C1 (0.894 g, 1.62 mmol) in CH3CN ( 10 ml). Gas evolved and the color changed to yellowbrown. The mixture was warmed to room temperature and stirred for another hour. Solvents were removed in t,acuo leaving a brown solid; yield 1.10 g (98%): ~H NMR (CD~CN) 6 10.22 (br s, 2, N H ) , 7.84 (d, 2, ArH), 7.27 (d, 2, ArH), 7.12 (t, 2, ArH), 6.90 (t, 2, ArH), 2.49 (s, 15, Cp*); IR (KBr, Nujol) cm ~ 3352 (v~H). Anal. Calc. for C22H2sCIF6N3PW: C, 37.98; H, 3.62; N, 6.04. Found: C, 37.76; H, 3.65; N, 6.10. Cp*W[HNNNH]01~-NNMe2) (Sa). 1,1-Dimethylhydrazine (38/~1, 0.51 retool) was added to a yellowbrown solution of [Cp*W[HNNNH]CII PF6 C0.116 g,
756
S. Cai et al.
0.17 mmol) in CH3CN (15 ml) at - 40"C. The solution changed to green, then a yellow precipitate formed. The mixture was allowed to warm to room temperature and was stirred for 30 rain. The reaction mixture was filtered and the yellow solid was washed with cold CH3CN (5 ml) and dried in vacuo: yield 0.035 g (37%): ~H N M R (C6D6) 6 8.11-6.90 (m, 8, ArH), 6.35 (s, 2, NH), 3.04 (s, 6, NNMe2), 1.50 (s, 15, Cp*); ~H N M R (CD2C12) 6 7.86 6.75 (m, 8, ArH), 6.69 (s, 2, NH), 3.63 (s, 6, NNMe2), 1.60 (s, 15, Cp*); ~3C{~H} NMR (CD2C12) 0 153.5 115.0 (6 singlets, ARC), 111.8 (s, CsMe5), 48.9 (s, NNMe2), 10.4 (s, CsMes). Anal. Calc. for C24H31N5W: C, 50.27; H, 5.45: N, 12.21. Found: C, 50.64; H, 5.22; N, 12.26. Cp*W[HNNNH](N-i-Pr) (Sb). A solution of iPrNH2 (0.49 ml, 5.75 mmol) in CH3CN (5 ml) was added dropwise to a brown solution of [Cp*W[HNNNH]CI}PF6 (1.00 g, 1.44 retool) in CH3CN (10 ml) at -40"C. The solution changed to red immediately and a red precipitate formed. The mixture was warmed to room temperature and stirred for 16 h. The mixture was then cooled to - 4 0 ° C and allowed to stand at this temperature for 12 h. The red solid was collected by filtration and washed with cold CH3CN (5 ml). It was then extracted with toluene until the extracts were colorless. Solvents were removed from the combined extracts to give the red product: yield 0.575 g (70%): ~H NMR (CD2CI2) 7.75 6.68 (m, 8, ArH), 6.49 (s, 2, NH), 5.63 (septet, 1, NCHMe2), 1.74 (s, 15, Cp*), 1.29 (d~ 6, NCHMe,). Anal. Calc. for C,sH32N4W: C~ 52.46; H, 5.63; N, 9.79. Found: C, 52.17; H, 5.83; N, 9.71. Cp*W[HNNNH](O) (9). This complex could be prepared either from {Cp*W[HNNNH]C1}PF6 or {Cp*W[HNNNH]CI}OTf. Degassed H20 (29/~1, 1.61 retool) was added to a mixture of {Cp*W [HNNNH]CIlOTf (0.750 g, 1.07 retool) and K2CO3 (0.760 g, 5.50 mmol) in CH3CN (20 ml) at 0'C. The mixture was stirred at 0':C for 2 h, then warmed to room temperature and stirred for another 18 h. The volatile components were removed in vacuo. The residue was extracted with dichloromethane until the extracts were colorless. Dichloromethane was removed from the combined extracts in vacuo and the brown crystalline solid was washed with CH3CN (2 x 5 ml) and dried in vacuo ; yield 0.555 g, 98%7 : IH N M R (CDCI3) 6 7.80-6.76 (m, 8, Ark/), 6.59 (s, 2, NH), 1.83 (s, 15, Cp*); 1R (KBr, Nujol) cm i 3376 and 3247 (VNH), 885 (Vwo). Anal. Calc. for C~2H25N3OW : C, 49.73 ; H, 4.74; N, 7.91. Found: C, 49.84 ; H, 5.07 : N, 7.87. Cp*W[HNNNH]Me (10). ZnMe2 (0.16 ml, 2.32 mmol) was added to a suspension of Cp*W [HNNNH]C1 (0.920 g, 1.67 mmol) in toluene (15 ml). The reaction flask was sealed with a septum and was heated at 80~C for l h. The solution changed to redpurple and a green solid deposited. The mixture was cooled to room temperature and filtered. The green solid was washed with toluene until the washings were almost colorless. The residue was extracted with
diethyl ether until the extracts were colorless. The combined ether extracts were chromatographed on a short alumina column using diethyl ether as eluent solvent. A red-purple band was collected. The volume of the solution was then reduced to ~ 3 ml 01 racuo. The solution was cooled to - 4 0 : C . The red-purple solid was collected by decanting the supernatant liquid and was dried in vacuo: yield 0.570 g (64%): ESR (CH2C12) 9 = 1.98; Av~2 = 17.3 g. Anal. Calc. for C~3H2~N3W: C, 52.09; H, 5.32; N, 7.92. Found: C, 52.39 ; H, 5.42 ; N, 7.89. {Cp*W[HNNNH]Me}OTf (11). M e t h o d A. A cold (-40'~'C) solution of Cp*W[HNNNH]Me (0.114 g, 0.21 mmol) in CH2C12 (5 ml) was added quickly to a suspension of triflic acid (19 pl, 0.21 mmol) in CH2C12 (10 ml) at -40"C. The mixture was slowly warmed to room temperature and stirred for 3 days. The solution gradually changed from red-purple to green and a small amount of white solid formed. The mixture was filtered through a frit and the green filtrate reduced in volume (3 ml). Diethyl ether (15 ml) was layered on top. Green crystals grew slowly at 2TC. The crystals were isolated by decanting the mother liquor; yield 95 mg (65%): ~H NMR (CD3CN) 6 9.80 (br s, 2, NH), 7.68 (d, 2, ArH), 7.07 (t, 2, ArHL 7.05 (d, 2, ArH), 6.85 (t, 2, ArH), 2.31 (s, 15, Cp*), 0.71 (s, 3, Me). Anal. Calc. for C24H28F3N303SW : C, 42.43 ; H, 4.15 ; N, 6.18. Found: C, 43.01 ; H, 4.26; N, 6.50. M e t h o d B. To a purple solution of Cp*W [HNNNH]Me (0.300 g, 0.57 retool) in THF (5 ml) was added dropwise a solution of AgOTf (0.145 g, 0.57 mmol) in THF (5 ml) at room temperature. A silver mirror formed immediately and a green solid deposited. Acetonitrile (10 ml) was added to the reaction mixture and the mixture was stirred for 30 min. The resulting mixture was filtered through a medium frit bedded with Celite. The green filtrate was reduced to ~ 3 ml b7 vacuo. Diethyl ether (15 ml) was layered on top. Green crystals formed with time at room temperature. The crystals were collected by decanting the supernatant liquid and dried hi t,acuo; yield 0.353 g (92%). Cp*W[(2-N-C6H4)(2'-NH-C6H4)N]Me (12). DBU (27.3 pl, 0.18 mmol) was added to a green slurry of {Cp*W[HNNNH]Me}OTf (0.124 g, 0.18 mmol) in CH.,CI2 (10 ml) at - 4 0 ' C . The color of the solution changed to red immediately. The mixture was warmed to room temperature and stirred for 1 h. All volatile components were removed in vacuo and the residue was extracted with diethyl ether until the extracts were colorless. The solvents were removed from the red extracts to give a red solid; yield 0.080 g (83%): IH N M R (CD2C12) 6 8.25 (br s, 1, NH), 7.54-6.26 (m, 8, ArH), 2.01 (s, 15, Cp*), 0.46 (s, 3, Me); IH NMR (CDCI3) 6 8.17 (br s, 1, NH), 7.61 6.30 (m, 8, ArH), 2.01 (s, 15, Cp*), 0.54 (s, 3, M e ) ; 13C{~H} NMR (CDC13) 6 158.8 114.6 (11 singlets, ARC), 113.6 (s, CsMe5), 18.4 (s, W M e ) , 11.2 (s, CsMes). Anal Calc. for C23H27N3W: C, 52.19; H, 5.14; N, 7.94. Found: C, 52.61 ; H, 5.30; N, 8.15.
Molybdenum and tungsten Cp* complexes
Crystal structure o[ {Na[O(C2Hs)2]Cp*Mo[HNNO]CI}2 (3). An orange-brown prismatic crystal of dimension 0.25 x 0.28 x 0.47 mm was mounted in a glass capillary in a nitrogen atmosphere. The data were collected at room temperature on a Rigaku diffractometer with a graphite-monochromated M o K~ radiation (2 = 0.71069 A). Of the 3276 reflections that were collected, 3131 were unique, and equivalent reflections were merged. The intensities of three representative reflections measured after every 150 reflections remained constant throughout data collectiom obtained from a least-squares refinement using the setting angles of 23 carefully centered reflections in the range 13.94: < 20 < 20.44 '~ corresponded to a monoclinic cell with the dimensions a = 15.367(4) A, b = 20.850(37 A, c = 12.271(2) /k and /~ = 113.71(3) for Z = 4. Based on systematic absences the space group was determined to be C_, (#5). The calculated density is 1.456 g/cm 3. A numerical absorption correction, using the program DIFABS, was applied, resulting in transmission factors ranging from 0.76 to 1.32. The structure was solved by Patterson's method. The final cycle of full matrix least-squares refinement was based on 1288 observed reflections (1 > 4a(I)) and 91 variable parameters and converged (largest parameter shift was 3.8 times its esd) with unweighted and weighted agreement factors of R = 0.082 and R, = 0.091. The maximum and minimum peaks on the final difference Fourier correspond to 1.13 and - 0 . 9 3 e-//k 3, respectively. All calculations were performed using the TEXAN crystallographic software package. Due to a disorder problem the pentamethylcyclopentadienyl ligand and all phenyl rings were refined as rigid groups. Crystal structure q/CCp*Mo[HNNO](NH3) (5a). A green prismatic crystal with dimensions 0.3 x 0.2 x 0.2 mm was mounted on a glass fiber under a stream of cold nitrogen gas from a liquid nitrogen bath. Data were collected at 72:C on an Enraf-Nonius CAD 4 diffractometer with a graphite-monochromated M o K~ radiation (2 = 0.71069/~). Of the 8525 reflections that were collected, 4146 were unique, and equivalent reflections were merged. The intensities of three representative reflections measured after every 60 min remained constant throughout data collection, obtained from a least-squares refinement using the setting angles of 25 carefully centered reflections in the range 18.00: < 20 < 26.00 :~ corresponded to a tetragonal cell with the dimensions a = 19.105(2) A and c = 12.271(2) A for Z = 8. Based on systematic absences the space group was determined to be P4,.n (#86). The calculated density is 1.322 g/cm 3. An empirical absorption correction, based on azimuthal scans of five reflections, was applied, resulting in transmission factors ranging from 0.95 to 1.00. The structure was solved by Patterson's method. The final cycle of full matrix least-squares refinement was based on 2044 observed reflections (I > 4a(/)) and 252 variable parameters and converged (largest parameter shift was 0.00 times its esd) with unweighted and weighted
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agreement factors of R = 0.045 and R,. = 0.037. The maximum and minimum peaks on the final difference Fourier correspond to 0.47 and - 0 . 6 9 e - / A 3, respectively. All calculations were performed using the TEXAN crystallographic software package. Supplementary information covering experimental details, labelled ORTEP drawing, final positional parameters, final thermal parameters, and final observed and calculated structure factors for [NaO(C_,Hs), Cp*Mo[(2-NH-C6H4)(2'-O-C6H4)N]C1}2 (16 pp) and Cp*Mo[(2-NH-C6H4)(2'-O-C,,H4)N](NH3) (20 pp) is available upon request.
Acknowledgements--R.R.S. thanks the National Institutes of Health for support (GM 341978) and R.R.K. thanks the German AcademicExchange Servicefor a HEP postdoctoral fellowship.
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