Early Metal Thiolato Species as Metalloligands in the Formation of

Complexes Cp,Ti(SMe), (1) and Cp,V(SMe), (2) have been prepared and structurally characterized. These complexes are isostructural, both crystallizing ...
0 downloads 0 Views 987KB Size
Download PDF
2836

Organometallics 1989, 8 , 2836-2843

Early Metal Thiolato Species as Metalloligands in the Formation of Early/Late Heterobimetallic Complexes: Syntheses and Molecular Structures of Cp,Ti(SMe),, Cp,V(SMe),,

Teresa A. Wark and Douglas W. Stephan" Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, Canada N9B 3P4 Received May 25, 1989

Complexes Cp,Ti(SMe), (1) and Cp,V(SMe), (2) have been prepared and structurally characterized. These complexes are isostructural, both crystallizing in the tetra onal space group p41212. For 1, a = 9.288 while for 2, a = 9.276 (4) A, c = 14.164 (5) 8, = 9.288 (5) A, c = 14.487 (5) A, 2 = 4, and V = 1249 (1) (4) A, 2 = 4, and V = 1218 (1) A3. Reactions of these early metal thiolato species with Ni(COD), have been studied. Complex 1 acts as a metalloligand affording the complex (Cp,Ti(p-SMe),),Ni (3). Equilibria involved in the formation of 3 are shifted by addition of PCy, affording the complex Cp2Ti(p-SMe),NiPCy3 (5). Complex 3 crystallizes in the tetragonal space group 14, with a = 8.100 (2) A, c = 20.021 (6) A, 2 = 2, and V = 1316 (1) A3. The structural data for 3 are consistent with the presence of dative donor bonds between the electron-rich, dO ' Ni center and the electron-poor, do Ti atoms. A similar reaction of 2 with Ni(COD), results in redox chemistry affording the Ni(I1) s ecies (Ni(p-SMe)& (6). Complex 6 crystallizes in the monoclinic space group P 2 1 / n , with a = 11.393 (3) b = 11.483 (3) A, c = 11.821 (4) A, 2 = 2, and V = 1547 (1) A3. Complex 6 is a cyclic Ni(I1) hexamer in which methanethiolate groups bridge the Ni centers. The mechanism of formation of 6 may involve an electron-transfer process that proceeds through a V analogue of 3.

i3,

1,

Introduction Interest in homogeneous complexes containing both early, oxophilic and late, electron-rich metal centers has arisen as a result of the potential applications in carbon oxide reduction chemistry.' Such heterobimetallic complexes combine the Lewis acidity of the early metals with the known abilities of the late metals for hydrogen activation. Interest in such species is also prompted by the observation of strong metal-support interactions in heterogeneous catalytic systems., Direct electronic communication between the late metal centers and the early metals of the supports is postulated to account for the unique reactivity. Numerous recent studies have developed synthetic routes to a variety of early/late heterobimetallic complexes and examined the nature and degree of metal-metal interactions in such species as well as investigated the effects of metal atom proximity on the chemistry of the constituent metals. Much of this work has been recently reviewed.' Our approach to the synthesis of complexes containing such early/late metal combinations involves the use of functionalized early metal complexes as metall~ligands.~-'~For example, we have described a number of heterobimetallic complexes in which (1) Recent examples of early/late heterobimetallic systems have been cited in ref 3-12 and reviewed in: Stephan, D. W. Coord. Chem. Reu. 1989, 95, 41. (2) Baker, R. T. K., Tauster, S. J., Dumesic, J. A., Eds. Strong Metal-Support Interactions; American Chemical Society: Washington, DC, 1986. (3) White, G. S.; Stephan, D. W. Inorg. Chem. 1985,24, 1499. (4) White, G. S.; Stephan, D. W. Organometallics 1987, 6, 2169. (5) White, G. S.; Stephan, D. W. Organometallics 1988, 7, 903. (6) Wark, T. A.; Stephan, D. W. Inorg. Chem. 1987,26, 363. (7) Gelmini, L.; Stephan, D. W. Inorg. Chim. Acta 1986, 1 1 1 , L17. (8) Gelmini, L.; Stephan, D. W. Inorg. Chem. 1986,25, 1222. (9) Gelmini, L.; Stephan, D. W. Organometallics 1988, 7, 849. (10) Gelmini, L.; Matassa, L. C.; Stephan, D. W. Inorg. Chem. 1985, 24, 2585. (11) Zheng, P. Y.; Nadasdi, T. T.; Stephan, D. W. Organometallics 1989, 8, 1393. (12) Zheng, P. Y.; Stephan, D. W. Can. J . Chem. 1989, 1393.

0276-7333/89/2308-2836$01.50/0

thiolate bridges link the constituent metal centers. Ti/Cu,3 Ti/Ni,4 and Ti/Rh5 systems based on pendant phosphine-thiolate metalloligands have been described. The form of these complexes is shown below.

L

J

L

J

M = Rh, n = 1; M=Ni; n = O

Related heterobimetallic complexes in which simple early metal thiolate complexes act as metalloligands have also been described. For example, the complexes of the form Cp,Ti(p-SR),M(CO), (M = Cr, Mo, W) have described by several group^.'^-'^ The chemistry of such species has been investigated by Rauchfuss et al.*O Reports describing related thiolato-bridged complexes containing Ti or V metalloligands and later transition metals are limited to the complexes of the form [Cp2Ti(pSR),CUL]+~P~' and [Cp,Ti(p-SR)2NiCp]+.22 (13) Davies, G. R.; Kilbourn, B. T. J. Chem. SOC.A 1971, 87. (14) (a) Kopf, H.; Rathlein, K. H. Angew. Chem., Int. Ed. Engl. 1969, 8, 980. (b) A previous report of a crystallographic study of molecule 1 appears in: De C. T. Carrondo, M.A.A.F.;Jeffrey, G. A. Acta Crystallogr. 1983, C39, 42. (15) Braterman, P. S.; Wilson, V. A.; Joshi, K. K. J. Chem. SOC.A 1971, 191. (16) Cameron, T. S.; Prout, K. C.; Rees, G. V.; Green, M. L. H.; Joshi, K. K.; Davies, G. R.; Kilbourn, B. T. J. Chem. SOC.,Chem. Commun. 1971, 14. (17) Braterman, P. S.; Wilson, V. A.; Joshi, K. K. J.Organomet. Chem. 1971, 31, 123. (18) Joshi, K. K.; Wardle, R.; Wilson, V. A. Inorg. Nucl. Chem. Lett. 1970, 6, 49. (19) Kotz, J. C.; Vining, W.; Coco, W.; Rosen, R.; Dias, A. R.; Garcia, M. H. Organometallics 1983, 2, 68. (20) Ruffing, C. J.; Rauchfuss, T. B. Organometallics 1985, 4, 524. (21) Braterman, P. S.; Wilson, V. A. J. Organomet. Chem. 1971, 31, 131.

0 1989 American Chemical Society

Organometallics, Vol. 8, No. 12, 1989 2037

Early Metal Thiolato Species as Metalloligands

r

R

R

L

M = Cr, Mo, W; R = H, alkyl, Ph

1+

2

M = Cu, L = phosphine, R = Me M = Ni, L=Cp, R = Me

In this report we extend t h e chemistry of such early metal thiolate metalloligands. Herein, we describe the syntheses and structures of t h e complexes Cp,M(SMe), (M = Ti ( l ) ,V (2)) as well as the reaction chemistry of these species with Ni(COD),. Cp,Ti(SMe), (1) is shown t o a c t as a metalloligand yielding t h e heterobimetallic complexes ( C p , T i ( ~ 4 3 M e ) ~ ) ~ N(3) i and Cp,Ti(pSMe),NiPCy, (5). In contrast, t h e analogous reaction involving the V species 2 results in electron transfer affording t h e Ni(I1) hexamer ( N i ( ~ - s M e ) , ) ~ Both products 3 and 6 a r e characterized b y X-ray crystallographic methods. The results of these studies are presented, and the implications of these results are discussed. Experimental Section General Data. All preparations were done under an atmosphere of dry, 02-free N2 by using either Schlenk line or drybox techniques. Solvents were reagent grade, distilled from the appropriate drying agents under N2,and degassed by the freezethaw method at least three times prior to use. 'H NMR spectra were recorded on Bruker AC-300 spectrometer operating at 300 MHz. Trace amounts of protonated solvents were used as references, and chemical shifts are reported relative to SiMel. 31P{1H)NMR spectra were recorded using a Bruker AC-200 NMR spectrometer operating a t 81 MHz and are reported with 85% H3P04 as an external reference. Cyclic voltammetric experiments were performed using a BAS CV-27 potentiostat, a platinum disk working electrode, and a Ag/AgCl reference electrode. [NBu,] [BF,] was used as the supporting electrolyte. Combustion analyses were performed by Galbraith Laboratories Inc. Knoxville, TN. Cp2TiClzand Me& were purchased from the Aldrich Chemical Co., Cp,VC12 and Ni(COD)2 were purchased from the Strem Chemical Co., and PCy3 was purchased from Pressure Chemical co. Preparation of NaSMe. To a 100-mL THF solution of Me2S2 (15.7 mL, 87 mmol) was added 2 g (87 mmol) of sodium metal, and the mixture was stirred overnight. The air-sensitive sodium salt was filtered under nitrogen and dried in vacuo. Preparation of Cp2Ti(SMe), (1). To Cp2TiC12(1.0 g, 4.0 mmol) in 50 mL of THF was added NaSMe (563 mg, 8.0 mmol), and the mixture was stirred overnight. Activated neutral alumina was added and the mixture stirred for 10 min and filtered. The alumina was washed with 5 X 20 mL portions of THF that were combined with the mother liquor. The resulting THF solution was stripped to dryness and the residue washed with 2 X 10 mL of pentane. The red-purple microcrystalline solid was dried in vacuo (yield 1.0 g, 92%): 'H NMR (C6D6)6 6.23 (s, 10 H), 2.45 (s, 6 H). Anal. Calcd for Cl2HlBS2Ti:C, 52.94; H, 5.92. Found: C, 53.06; H, 5.95. Preparation of Cp2V(SMe)2(2). This compound was prepared in a manner analogous to that described for the corresponding titanium species, using 300 mg (1.2 mmol) of Cp2VClz and 167 mg (2.4 "01) of NaSMe. However, the reaction mixture was stirred for 4 h, followed by a similar workup, giving a dark blue-black microcrystalline solid (yield 200 mg, 61%): EPR,g = 1.997, a(SIV) = 58.75 G. Anal. Calcd for C12HlBS2VC, 52.35; H, 5.86. Found: C, 52.30; H, 5.80. Preparation of (Cp2Ti(pSMe)2)2Ni (3). To a 30 mL benzene solution of Cp2Ti(SMe)2(100 mg, 0.36 "01) was added Ni(COD), (50 mg, 0.18 mmol) in benzene. After the solution was stirred for 2 h, there was a gradual color change from red-purple to (22)Wemer, H.; Ulrich, B.; Schubert, U.; Hofmann, P.; Zmmer-gasser, B. J. Organomet. Chem. 1985,297, 27.

purple-black. The solvent was removed in vacuo, and the residue was washed with 2 x 10 mL of pentane. The solid was isolated by filtration and washed with 2 X 10 mL portions of pentane. The black microcrystalline product dried in vacuo (yield 65 mg, 60%): 'H NMR (C6D6)6 5.37 (s, 20 H), 2.19 (5, 12 H). Anal. Calcd for C24H32NiS4Ti2:C, 47.78; H, 5.35. Found: C, 47.70; H, 5.30. Preparation of Cp2Ti(p-SMe)2NiPCy3(5). To a 30-mL benzene solution of Ni(COD), (100 mg, 0.36 mmol) was added PCy3 (205 mg, 0.7 mmol). Cp,Ti(SMe), (100 mg, 0.36 mmol) in benzene was added dropwise to the reaction flask with stirring. The mixture was stirred for 2 h, after which the solution was stripped to dryness. The resulting residue was dissolved in pentane and the solution filtered giving a purple-black solution and a gray solid. The pentane solution was stripped to dryness, giving a purple-black oily solid that solidified upon standing. The solid was washed with 5 mL of diethyl ether, the solvent decanted, and the residue dried in vacuo (yield 104 mg, 50%): 'H NMR (CP,) 6 5.28 (s, 10 H), 2.17-1.07 (br m, 39 H); 31P(1H)NMR ( c & ) 6 58.3. Anal. Calcd for C&149NiPS2Ti: C, 58.93; H, 8.08. Found C, 58.80; H, 7.90. Preparation of ( N i ( ~ - s M e ) (6). ~ ) ~ To a THF solution of Cp2V(SMe)2 (50 mg, 0.18 mmol) was added dropwise a T H F solution of Ni(COD)2 (25 nig, 0.09 mmol). Upon addition of Ni(COD)*, there was a gradual color change from green-black to brown. After being stirred for 3 h, the solution volume was reduced to 5 mL and pentane added to precipitate a brown solid that was isolated by filtration and dried in vacuo (yield 24 mg, 30%). Anal. Calcd for C12H36S12Ni6:c, 15.71; H, 3.96. Found: C, 15.20; H, 3.80. X-ray Data Collection and Reduction. Diffraction experiments were performed on a four-circle Syntex P2' diffractometer with graphite-monochromatized Mo K a radiation (A = 0.71069 A). The initial orientation matrices were obtained from 15 machine-centered reflections selected from rotation photographs. These data were used to determine the crystal systems and, in the case of 1, the reported cell parameters. Partial rotation photographs around each axis were consistent with tetragonal crystal systems for 1, 2, and 3 and a monoclinic crystal s y t e m for 6. The final lattice parameters and the orientation mal ices for 2, 3, and 6 were determined from 64, 64, and 45 high-angle data (20' < 20 < 25'), respectively. Crystal d7ta and data collection parameters are summarized in Table The observed extinctions were consistent with the space grot '41212 for 1 and were collected 2 , I J for 3, and P2Jn for 6. The +h,+k,+E d for 1,2, and 3 (4.5' < 28 < 45.0°), while for 6 f, t k , + l data were collected (4.5' < 20 < 45.0'). In each case, three standard reflections were recorded every 197 reflections. Their intensities showed no statistically significant change over the duration of the data collection. All data were collected at 24 'C, with a scan range of 1.0' below Kal and 1.0' above Ka2,using a background to scan time ratio of 0.5. The data were processed by using the SHELX-76 program package on the computing facilities at the University of Windsor. In the case of 3 and 6 an empirical absorption was applied to the data employing a locally modified version of ABSORB. S t r u c t u r e Solutions and Refinements. Non-hydrogen atomic scattering factors were taken from the literature tabulat i o n ~ . ~ The ~ - ~heavy ~ atoms positions for all structures were determined by using direct methods. The remaining non-hydrogen atoms were located from successive difference Fourier map calculations. The refinements were carried out by using full-matrix least-squares techniques on F, minimizing the function w(IF,I lFcl)2where the weight, w ,is defined as 4F:/2u(F:) and F, and F, are the observed and calculated structure factor amplitudes, respectively. In the final cycles of refinement, all the non-hydrogen atoms were assigned anisotropic temperature factors. Hydrogen atom positions were calculated and allowed to ride on the carbon to which they are bonded, assuming a C-H bond length of 0.95 A. Hydrogen atom temperature factors were fixed at 1.10 times (23)Cromer, D.T.;Mann, J. B. Acta Crystallogr., Sect. A: Cryst. Phys., Dzffr., Theor. Gen. Crystallogr. 1968, A24, 324. (24)Cromer, D. T.;Mann, J. B. Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1968, A24, 390. (25) Cromer, D. T.; Waber, J. T. International Tables for X-ray Crystallography; Kynoch Press: Birmingham, England, 1974.

2838 Organometallics, Vol. 8, No. 12, 1989

formula cryst color, form cryst system a, A

b, A c, A P , deg space group

v. A3

picalcd), g cm-3

z

cryst dimens, mm p, cm-' data collected no. of unique data F,2 > 3u(F,1) no. of variables R, % R,, % largest A/u final least-squares cycle max resid electron density, e/A3 atom associated

atom Ti

c1

c3 c5

(1)

(6) (5) (5)

v c1 c3 c5

-431 -1339 -2280 -2324

Ti S c2 c4 C6

0 -1147 (2) 7403 (8) 8977 (9) -3376 (7)

Nil Ni3 52 s4 S6

c2

c4 C6

Table I. Crystallographic Parameters molecule 1 molecule 2 C1ZH16SZTi C12H16S2V dark red prisms brown blocks tetragonal tetragonal 9.288 (5) 9.276 (4)

molecule 3 C24H32NiS4Ti2 black blocks tetragonal 8.100 (2)

14.487 (5)

14.164 (4)

20.021 (6)

P41212 1249 (1) . . 1.45 4 0.48 X 0.29 9.10 988

P41212 1218 (1) 1.50 4 0.46 X 0.27 10.46 957

I4

X

0.38

771 68 2.76 3.19 0.001 0.28 Ti

(1)

(6) (5) (5)

4459 (1) 6577 (1) 2766 (1) 2972 (1) 6089 (1) 2853 (6) 4183 (6) 6829 (6)

2

3

-2039 (2) 1398 (9) 1966 (11) -2101 (8)

Molecule 1391 (1) 10576 (1) 1297 (3) 2182 (4) 10444 (3) Molecule 6906 (lj 6238 (1) 6036 (1) 5443 (1) 7884 (1) 4702 (5) 6150 (5) 8240 (6)

6

6111 (1) 7074 (1) 5993 (1) 2230 (1) 6316 (1) 6751 (5) 1494 (5) 4958 (5)

0

black blocks monoclinic 11.393 (3) 11.483 (3) 11.821 (4) 90.08 (2) mlln 1547 (1) 0.98 n

z

L

0.31

742 68 3.66 4.39 0.003 0.37 v,s

Molecule loo00 8499 (3) 9507 (3) 9130 (3)

C12H36Ni6S12

n

X

0.46 X 0.15 15.42 1133

X

0.19

0.004

0.69 Ni

S

c2

c4 C6

0.31 X 0.15 X 0.23 42.44 2285 1503 136 2.85 3.05 0.002 0.58 n12

760 71 3.50 3.93

Table 11. Positional Parameters' z atom Molecule 1 -361 (1) loo00 S -538 (5) 8486 (3) c2 1090 (6) 9465 (3) c4 -1251 (6) 9096 (3) C6 -431 (1) -596 (6) 1083 (6) -1283 (6)

molecule 6

1316 (1) 1.53

Y

X

-361 -1350 -2308 -2299

Wark and Stephan

X

Y

2

1696 (1) -1366 (5) -2849 (5) 3318 (5)

81 (1) 935 (5) -249 (7) 138 (6)

9038 (1) 8721 (3) 9706 (3) 9739 (4)

1709 (1) -1323 (5) -2859 (5) 3275 (5)

91 (1) 8812 (5) -200 (7) 284 (6)

9056 (1) 8752 (3) 9752 (3) 9810 (4)

Ni

c1

0

c3 c5

7201 (8) 8477 (8) 8171 (9)

97 (10) 2549 (9) 466 (12)

1753 (3) 1550 (4) 2310 (4)

Ni2

2917 (1) 4193 (1) 1924 (1) 4858 (1) 3364 (6) 631 (5) 4856 (6)

4117 (1) 4231 (1) 4077 (1) 7936 (1) 4131 (6) 3172 (6) 8798 (5)

5744 (1) 7145 (1) 4122 (1) 6410 (1) 8450 (5) 4264 (6) 7701 (5)

s1 s3 s5

c1 c3 c5

0

0

Positions multiplied by lo4. the isotropic temperature factor of the carbon atom to which they are bonded. In all cases the hydrogen atom contributions were calculated, but not refined. The final values of R and R, are given in Table I. The maximum A/u on any of the parameters in the final cycles of the refinement and the location of the largest peaks in the final difference Fourier map calculation are also given in Table I. The residual electron densities were of no chemical significance. The following data are tabulated: positional parameters (Table 11) and selected bond distances and angles (Table 111). Thermal parameters (Table Sl),hydrogen atom parameters (Table S2), and values of 10Fo and lOF, (Table S3) have been deposited as supplementary material.

Results and Discussion The known complex C P , T ~ ( S M (~1)14* ) ~ was prepared by reaction of Cp2TiC12with 2 equiv of NaSMe in THF. The product is separated from small amounts of unreacted Cp2TiC12as well as monosubstitution product Cp2TiC1(SMe) by stirring the reaction mixture with activated

neutral alumina. Filtration and removal of solvent afford the dark red-purple, microcrystalline product 1 in 92 % yield. The 'H NMR spectrum of 1 shows singlet resonances attributable to the cyclopentadienyl and methyl moieties.

The analogous V complex C P ~ V ( S M(2) ~ )was ~ prepared in a similar manner to that used for 1. Reaction of Cp2VC12 with 2 equiv of NaSMe followed by treatment with alumina and subsequent isolation affords microcrystalline, blue-black 2 in 61% yield. In similar reactions of Cp2VC1, with HSPh and NES, reduction of V(IV) to V(II1) resulted in the formation of Cp2V2(p-SPh)4.26 Some degree of reduction in the present reaction may account for the comparatively low yield of 2. Further, it may also explain the observed sensitivity of yields to variations in scale, ~~

~~

(26) Muller, E. G.; Watkins, S. F.; Dahl,L.F.J. Organomet. Chem. 1976, 111, 73.

Organometallics, Vol. 8, No. 12, 1989 2839

Early Metal Thiolato Species as Metalloligands

Ti-S Ti-C3 S-C6 c3-c4

2.400 (1) 2.385 (4) 1.817 (5) 1.386 (8)

S-Ti-S’

93.7 (1)

v-s

v-c3 S-C6 c3-c4

2.442 (1) 2.324 (4) 1.811 (5) 1.351 (8)

s-v-S’

88.7 (1)

Ti-S Ti-C1 Ti-C4 C2-C3 Cl-C5

Table 111. Selected Bond Distances and Angles Molecule 1 Distances (A) Ti41 2.383 (4) Ti44 2.352 (5) Cl-C2 1.409 (6) c4-c5 1.381 (7)

2.503 (2) 2.384 (6) 2.396 (7) 1.37 (1) 1.40 (1)

C6-S-Ti

Angles (deg) 109.9 (2)

Molecule 2 Distances (A) v-c 1 2.292 (4) v-c4 2.289 (5) Cl-C2 1.416 (7) c4-c5 1.426 (7) Angles (deg) 110.4 (2)

C6-S-V

Ni-S Ti-C2 Ti-C5 c3-c4 Ti . Ni

.

Molecule 3 Distances (A) 2.220 (1) 2.400 (6) 2.392 (7) 1.41 (1) 2.786 (1)

Ti42 Ti45 C2-C3 Cl-C5

Cp-Ti-Cp’

2.399 (4) 2.375 (4) 1.396 (6) 1.412 (7) 127.0 (1)

v42 v-c5 C243 Clc5

2.300 (4) 2.286 (5) 1.403 (6) 1.428 (7)

cp-v-Cp‘

130.2 (1)

S-C6 Ti43 c1c2 c4-c5

1.828 (6) 2.429 (6) 1.41 (1) 1.40 (1)

Angles (deg) Ti-S-Ni S-Ni-S Cp-Ti-Cp’

72.0 (1) 105.6 (1) 129.3 (1)

s4-c4 Nil-Ni2

2.198 (2) 2.199 (1) 2.225 (2) 2.203 (1) 1.814 (7) 1.821 (6) 3.195 (1)

Nil-S1-Ni2 Nil-S6-Ni3 Sl-Nil-S:! S1-Nil-S6 S5-Nil-S6 S2-Ni2-S3 S5-Ni3-S6 C2-S2-Nil C4-S4-Ni2 C6-S6-Nil

93.0 (1) 78.0 (1) 83.0 (1) 98.9 (1) 82.2 (1) 96.7 (1) 82.6 (1) 109.4 (2) 113.9 (2) 114.8 (2)

Nil-S1 Nil-S6 Ni2-S3 Ni3-S4

s1-c1

98.6 (1) 118.7 (2)

S-Ni-S’ C6-S-Ni

117.4 (1) 111.1 (2)

Molecule 6 Distances (A) Nil-S2 2.188 (2) Ni2-S1 2.206 (2) Ni2-S4 2.197 (2) Ni3-S5 2.204 (2) s2-c2 1.805 (6) s5-c5 1.819 (6) Nil-Ni3 2.771 (1)

Nil-S5 Ni2-S2 Ni3-S3 Ni3-S6 s3c3 S646 Ni2-Ni3

2.224 (2) 2.188 (2) 2.201 (1) 2.204 (2) 1.812 (7) 1.822 (6) 2.774 (1)

S-Ti-S’ C6-S-Ti

Angles (deg) Nil-S2-Ni2 Ni2-S3-Ni3 Sl-Ni2-S2 S2-Nil-S5 Sl-Ni2-S3 S2-Ni2-S4 C1-S1-Nil C2-S2-Ni2 C5-S5-Nil C6-S6-Ni3

concentration, and duration of reaction. The formulation of 2 as a V(1V) species is substantiated by the EPR spectrum. The spectral parameters and eight-line pattern, resulting from coupling of the unpaired electron to a 51V nucleus ( ( g ) = 1.997, ( a ) = 58.75 G ) is typical of EPR spectra of CpzVLz specie^.^^*^^*^ X-ray structural studies for 1 and 2 showed that the compounds are isostructural (Figure l).14b In both cases, the crystals are made up of tetragonal unit cells each containing four discrete formula units. The closest approach between these molecules is 2.876 A (S--H5) in 1 and 2.629 A (H6A-.H2) in 2. The symmetry of the unit cells demands that the metal atoms of 1 and 2 sit on a crystallographically imposed 2-fold axis of symmetry. The coordination spheres, of both the Ti of 1 and the V of 2, are comprised of two .rr-bondedcyclopentadienyl rings and two methanethiolato moieties. Thus, the molecular geometries about the metal centers are best described as pseudotetrahedral with strict C2 symmetry. The imposed symmetry requires that the two cyclopentadienyl rings are exactly eclipsed. This is in contrast to that seen for

93.8 (1) 77.6 i i j 82.8 (1) 96.9 (1) 169.0 (1) 177.1 (1) 104.1 (2) 109.4 (2) 106.9 (2) 115.1 (2)

Nil-S5-Ni3 Ni2-S4-Ni3 S1-Nil-S5 S2-Nil-S6 Sl-Ni2-S4 S3-Ni2-S4 C1-S1-NIP C3-S3-Ni2 C5-S5-Ni3

77.5 (1) 78.2 (1) 171.0 (1) 175.4 (1) 99.3 (1) 81.6 (1) 107.0 (2) 110.2 (2) 108.9 (2)

Figure 1. ORTEP drawing of molecule 1 (20% thermal ellipsoids are shown). Hydrogen atoms are omitted for clarity. The labeled atoms are symmetry related to their unlabeled counterparts. The labeling scheme for 2 is identical with that shown here with the obvious replacement of T i with V.

Cp2M(SPh), (M = Ti, V) where the rings are rotated by 1 5 . 5 O with respect to one another.% The accessibility of the eclipsed conformation in 1 and 2 may reflect the lesser steric demands of the methanethiolate substituents versus those of the benzenethiolato ligands.

Wark and Stephan

2840 Organometallics, Vol. 8, No. 12, 1989 Scheme I

1

4

5

3

lies in the MS2 plane, perpendicular to the vector that bisects the S-M-S angle. Population of this nonbonding orbital by a single unpaired electron in d' complexes results in electrostatic repulsions that decrease the S-M-S angle. Employing extended Huckel methods, calculations were 70 86 94 102 performed in which S-M-S angles of the model systems Cp,M(SH), (M = Ti, V) were optimized on the basis of S-M-S ANGLE 0 the minimization of the total energy. The results of these Figure 2. Plots of total energy for CP~M(SH)~ (M = Ti, V) vs calculations are shown graphically in Figure 2. Analogous the S-M-S angle. The energy scale is in divisions of 0.05 eV. The calculations for Cp2MH, described by Lauher and Hoffenergy scales for the two plots are shifted relative to each other to allow presentation on the same figure. man33for Cp,MH, show similar but less distinct potential wells. The S-M-S angle values at minimum energy were The average M-C distances of 2.379 A in 1 and 2.298 found to be 93.5" and 87" for the Ti and V models, reA in 2 are similar to those seen in the related Cp,M(IV) spectively. Interestingly, the S-M-S found in 1 and 2 complexes (M = Ti, V), r e ~ p e c t i v e l y . ~ -The ~ ~ 0.1-A * ~ ~ ~ ~ ~ approach ~ these predicted values for the Cp,M(SH), difference in the V-C and Ti-C bond lengths is consistent models. This further suggests that the larger S-M-S anwith the difference in covalent radii for V (1.22 A) and Ti gles seen for the complexes Cp,M(SPh), (M = Ti, V) are (1.32 A). The Ti-S distance of 2.400 (1) A is shorter than a result of steric demands of the substituents. Extended that seen for Cp,Ti(SPh), (2.4395 (8), 2.424 (8) A),26 Huckel calculations also suggest that for Cp,ML2 systems, CP*~T~(SH (2.409 ) ~ (2), 2.418 (3) Cp2Ti(SPCy& the better the r-acceptor ability of the ligand, the greater (2.4203 (3), 2.427 (3) A),29and a number of other Cp2Tithe bending of the Cp,M fragment and, thus, the smaller (SR), complexes in which the sulfur containing ligand is the Cp-M-Cp angle. This is consistent with the present a chelate (2.416 (5)-2.42 (1) A).3w32 In a similar fashion, observations as the Cp-M-Cp angles (i.e., the angle bethe V-S distance of 2.442 (1) 8, in 2 is shorter than those tween the vectors joining the M and the centroids of the seen in Cp,V(SPh), (2.448 (3), 2.470 (2) A).26 These difCp rings) were found to be 127.0 (1)" and 130.2 (1)" for ferences may be attributed to the basicity and small steric 1 and 2, respectively; significantly smaller than the cordemands of the methanethiolato ligand. One exception responding angles found in Cp,(SPh), (M = Ti, 132.4'; M to this trend is Ti-S distances found in the species = V, 134.6°).26 Cp2Ti(SCH,CH2CH2PPhz)2(2.378 (6), 2.384 (6) A)5which Reactions of 1 with Ni(COD), were studied. Initially are shorter that those in 2. The reasons for this are not the Ni species was reacted with 2 equiv of 1. The purclear. ple-red solution of Ni(COD)2 and l gradually darkened The S-M-S angles in 2 (88.7 (1)O) and 1 (93.7 (1)")are over a 2-h period to a purple-black color. Removal of the significantly smaller than those seen in the related comsolvent and washing the residue with pentane yielded black plexes C P , M ( S P ~ (M ) ~ = V, 94.1 (1)O; M = Ti, 99.3 (1)"),% microcrystalline product 3. The 'H NMR spectrum of 3 reflecting the lesser steric demands of the methanethiolato showed resonances attributable to both cyclopentadienyl ligand. The differences in geometry of the do Ti species and methanethiolato fragments. The differences between and the d' V complex are consistent with predictions from the chemical shifts of compounds 3 and 1 were consistent extended Huckel calculation^^^ as well as the results of with coordination of the methanethiolato groups of 1 to single-crystal EPR ~tudies.3~ Such work has shown that Ni, thus bridging the two metal centers. The absence of the single unpaired electron of d' complexes occupies the COD resonances in the 'H NMR spectrum of 3 as well as molecular orbital derived from the lal frontier orbital of the reaction stoichiometry and combustion analyses data Cp,M fragment. For the present complexes such an orbital suggest the formulation of 3 as (Cp,Ti(p-SMe),),Ni. This formulation was confirmed by a crystallographic study (vide infra). (27) Benecke, J.; Drews, R.; Behrens, U.; Edelmann, F.; Keller, K.; Roesky, H. W. J. Organomet. Chem. 1987, 320, C31. The complex Cp,Ti(p-SMe),Ni(COD) (4) may be pos(28) Bottomley, F.; Drummond, D. F.; Egharevba, G. 0.;White, P. S. tulated as an intermediate in the formation of 3. Attempts Organometallics 1986,5, 1620. to spectroscopically observe and/or isolate this species (29) Gelmini, L.;Stephan, D. W. Organometallics 1988, 7, 1515. directly from reactions of 1 equiv of 1 with Ni(COD), were (30) Kutoglu, V. A. 2.Anorg. Allg. Chem. 1972, 390, 195. (31) Kutoglu, V. A. Acta Crystallogr., Sect. B 1973, B29, 2891. unsuccessful. In all cases, resonances attributable only to (32) Bolinger, C. M.;Rauchfuss, T. B. Znorg. Chem. 1982,21, 3947. compound 3 were observed and diminished yields of 3 (33) Lauher, J. W.; Hoffmann, R. J. Am. Chem. SOC.1976,98, 1729. obtained. These results suggest that the rate-determining (34) Petersen, J. L.; Dahl, L. F. J. Am. Chem. SOC.1974, 96,2248.

Organometallics, Vol. 8, No. 12, 1989 2841

Early Metal Thiolato Species as Metalloligands

'B

S

c6

Figure 4. Structural details of the TiSzNiSzTicore of 3. Fig-ure 3. ORTEP drawing of molecule 3 (20% thermal ellipsoids are shown). Hydrogen atoms are omitted for clarity. The labeled atoms are symmetry related to their unlabeled counterparts.

step in the formation of 3 is probably initial replacement of a COD on Ni with the chelating metalloligand 1 and that subsequent replacement of the remaining COD is rapid. Thus, the equilibrium involving 4 and 3 lies to the right (Scheme I). The position of this equilibrium is shifted by the addition of PCy3 to reaction mixtures of Ni(COD)2 with 1 equiv of 1. Solvent removal and washing of the residue with diethyl ether afford the isolation of compound 5 as a purple-black solid. The 31P(1H} NMR spectrum of 5 showed a single resonance at 58.3 ppm consistent with coordination of PCy3 to Ni. The 'H NMR spectrum showed resonances attributable to cyclopentadienyl, methyl, and cyclohexyl groups. These data as well as combustion analyses were consistent with the formulation of 5 as Cp,Ti(p-SMe),NiPCy,. This species is isoelectronic with previously reported complexes of the form [Cp,Ti(~-SE~)~CUPR~]+.~ An X-ray crystallographic study of 3 showed that the complex crystallizes in a tetragonal space group with two discrete molecules in the unit cell. The closest approach between the two molecules is 2.526 8, (H4--H5). The symmetry of the unit cell requires that the Ni atom occupies a special position with 3 symmetry and that the Ti atoms sit directly on a 2-fold axis of symmetry. Thus, the asymmetric unit is only one fourth of the trimetallic molecule. The geometry about both the Ti and Ni centers is best described as pseudotetrahedral (Figure 3). The coordination sphere of the Ti atoms is comprised of two a-bonded cyclopentadienyl groups and the two methanethiolato moieties, while the four symmetry-related sulfur atoms of the methanethiolato groups complete the coordination sphere of the Ni. The Ti-C bond distances are typical. The Ti-S bond length of 2.503 (2) 8, is substantially longer than the corresponding distance found in 1, as expected as a result of thiolate bridging to Ni. The Ni-S distance of 2.220 (1)8, is comparable to that found in Cp2Ti(p-SCH2CH2CH2PPh,),Ni,4and yet it is also considerably longer than the Ni-S bond lengths found in several Ni(I1) thiolate species (2.141 (2)-2.228 (2) 8,).4*35 These data as well as the pseudotetrahedral geometry are consistent with the formulation of 3 as a Ti(1V)-Ni(0) species. The TiS2NiS2Ticore of 3 is shown in Figure 4. Comparison of the structural parameters to those of a number of other early-late, thiolato-bridged heterobimetallics is facilitated by Table IV. The Ti-S-Ni angle in 3 is 72.0 (l)", which is the smallest Ti-S-M value reported. Angles at bridging atoms of less than 80" have been cited as ev(35) Rosenfield, S. G.; Wong, M. L. Y.; Stephan, D. W.; Marscharak,

P.K.Inorg. Chem. 1987,26,4119. (36) Wark,T. A.; Stephan, D. W., unpublished results, 1989.

Table IV. Thiolato-Bridged Early/Late Hete.robimetallicea compound M-M' M-S-M' S-M-S' S-M'-S' ref CpzTi(p-SMe)zMo3.321 (2) 82.4 (1) 99.9 (1) 94.d (1) 13 (CO), [Cp,Ti(p-S(CHz)3PPhz)zRhl+

3.127 (2)

83.2 (1) 81.5 i i j

96.8 (1)

100.1(1)

5

Cp,Ti(p-S(CHz)3PPhz)zNi

2.825 (2)

81.6 (1) 74.1 (2)

96.2 (2) 115.5 (2)

4

74.2 (1) 2.786 (1) 72.0 iij 2.846 (2) 73.5 (1) 74.1 (1) 3.024 (1) 78.1 (1) 2.803 (1)

117.4 (1)

97.5 (1)

106.4 (1)

this work 99.4 (1) 112.2 (1) 36 3

78.0 (1) 72.9 (1)

99.1 (2) 114.1 (2) 6

72.9 (2) 2.840 (1) 74.1 (1)

99.1 (1) 110.9 (1) 6

3.116 (2)

73.8 (1) 77.7 (1)

77.4 (1) 2.765 (5) 72.3 (3)

[(CpzTdrSMe)z)zPt]z+

98.6 (1)

101.8 (1)

103.1 (1) 42

98.0 (3) 106.0 (3) 37

2.776 (5) 72.6 (3) 97.8 (3) 104.4 (3) 72.7 (3) 72.3 (3) 2.788 (1) 70 (1) 104 (1) 115 (1) 38 2.809 (1) 71 (1) 70 (1) 69 (1)

105 (1)

109 (1)

"Distances are given A and angles in degrees; M and M' refer to the early and late metals, respectively.

idence for metal-metal intera~tion.lJ~J'.~' The S-Ti-S in 3 is 98.6 (1)"substantially greater than the corresponding S-Ti-S angle in 1 of 93.7 ( 1 ) O . The S-Ni-S angle of 117.4 (1)"is greater than expected for a tetrahedral Ni center and is also substantially larger than the S-M-S angles found in complexes containing simple dithio ligands.29 In some early-late heterobimetallics where metal-metal bonding has been implicated, core distortions from planarity have allowed a closer approach of the metal center~."'~In the present compound, presumably steric interactions between the two Cp,Ti(SMe), fragments precludes a "puckering" of the TiS2Ni cores. Consequently, the angular distortions about the TiS2Ni cores accommodate a close approach of the metal centers. The Ni-Ti distance of 2.786 (1)A is larger than the sum of the covalent radii (2.47 A); however, the Ti-Ni distance is 3 is shorter than the corresponding distance found in the isoelectronic Ti(1V)-Cu(1) complexes (Table IV). More generally, it is seen that for thiolato-bridged early/late heterobimetallics, the M-Ti distance decreases as the number of valence electrons on the late metal is increased. These trends are consistent with the presence of a weak, dative donation from the electron-rich, late metal to the electron-deficient, early metal center.

2842 Organometallics, Vol. 8, No. 12, 1989

Wark and Stephan

Compound 3 is isoelectronic with the d0-dl0-d0 complexes [Cp2Nb(p-SMe)2)2Ni]2+and [Cp2Ta(pa SMe)2)2Pt]2+.37.38 These cationic species have molecular geometries very similar to that of 3, although strict crystallographic symmetry is not seen for the Nb/Ni or Ta/Pt species. The metal-metal separations seen in the Nb-Ni species are 2.776 (5) and 2.765 (5) A, while in the Ta-Pt complex, the Ta-Pt distances are 2.788 (7) and 2.809 (7) A. These metal-metal separations are closer to the sum of the respective covalent radii (Nb/Ni 2.49 A,Ta/Pt 2.64 A) than that seen for 3. These data are consistent with an increased strength of the dative metal-metal interaction arising from the presence of a formal positive charge on d the early metal centers of the Nb-Ni and Ta-Pt species. c1 The notion of dative metal-metal bonding in these early/late heterobimetallic complexes is supported by theoretical calculations. For related phosphido-bridged Th-Ni and Th-Pt complexes, calculations reported by or ti^^^ are consistent with the presence of substantial dative metal-metal bonding. Although only preliminary results are available for models of thiolato-bridged early/late heterobimetallics, both extended Huckel and X a calculation for these systems suggest the presence of dative, metal-metal interactions.@ In the absence of detailed calculations, one might consider simple arguments in which Figure 5. ORTEP drawings of molecule 6 (a) is the view at 90° to (b) (20% thermal ellipsoids are shown). Hydrogen atoms are these early/late heterobimetallic systems are viewed as omitted for clarity. The labeled atoms are symmetry related to perturbations of the Cp2MH3 systems for which a full their unlabeled counterparts. frontier orbital treatment has been reported.33 The possibility of redox chemistry at one the metal of compound 6 crystallized from the reaction mixture. The centers of 1,2, or 3 was investigated by cyclic voltammetric combustion analyses were consistent with the empirical studies. A Pt electrode was used, employing [NBu4][BF4] formulation Ni(SMe),. as the electrolyte in THF with scan rates of between 200 A crystallographic study of 6 was undertaken. The and 500 mV/min. Complex 1 exhibited only a chemically compound crystallizes in a monoclinic system. The emirreversible wave at about +0.5 V attributable to ligand pirical formula units aggregate to give the hexamer (Nioxidation in the range of -1.70 to +1.00 V vs Ag/AgCl. ( P - S M ~ ) two ~ ) ~of , which occupy each unit cell (Figure 5). Complex 2 showed only chemically irreversible waves at The closest approach between the molecules is 2.37 A -0.95 and +0.75 V vs Ag/AgCl. Although it is uncertain, (H5B-eH2A). The coordination sphere of each Ni atom these features may arise from V(1V)-V(II1) and V(1V)-Vis comprised of four sulfur atoms each of which bridge to (V) redox chemistry. In the case of complex 3, features another Ni center. The Ni-S distances range from 2.188 were observed at +0.2 and +0.4 V vs Ag/AgCl. These (2) to 2.224 (2) A, which are typical of Ni(I1) thiolate waves may be attributable to the sequential oxidation of s p e ~ i e s . ~ S-C B ~ distance are also typical. The S-Ni-S Ni(0) to Ni(1) and Ni(I1) by comparison to similar potenangles where both sulfurs bridge the same two Ni atoms however, tials found for [Cp2Ti(p-SCH2CH2CH2PPh2)2Ni]o; are about 81-83’, while the S-Ni-S between adjacent the assignment is uncertain as the waves observed for 3 sulfur bridges is 96-99’. Thus, the coordination geometry were not reversible. Thus, in contrast to related thiolaat Ni is best described as pseudo-square-planar. The to-bridged early/late heterobimetallics (i.e., [Cp2Ti(pNi-S-Ni angles at S1 and S2 are 93.0 ( 1 ) O and 93.8 (l)’, SCH2CH2PPh,)2Cu]+,[Cp2Ti(p-SCH2CH2CH2PPh2)2Rh]+, respectively, resulting in a Nil-Ni2 separation of 3.195 and [Cp2Ti(p-SCH2CH2CH2PPh2)2Ni]0),3-5 no other oxi(1)A. In contrast, the Ni-S-Ni angles at S3, S4,S5, and dation states of 3 appear to be readily accessible. A similar S6 range from 77 to 78’ giving rise to Ni-Ni separations result was observed for the thiolato-bridged complexes of 2.771 (1)and 2.774 (1)A. These data demonstrate the [CP~T~(~-SE~)~CUL]+. It may be that the stability to redox range of angles that can be accommodated by a bridging chemistry of the phosphine-thiolate linked heterobithiolato sulfur atom. This tolerance of such geometric metallics is associated with the chelating nature of the variations at sulfur results in the cyclization of the present metalloligands. compound; that is, the two asymmetric units each conIn attempts to prepare related heterobimetallic species taining a Ni3(SMe)6fragment pair up, g k h g the hexameric containing d’ metal centers, the reaction of 2 with Ni(Cstructure. The geometry of the total molecule can be OD)2 was investigated. The reaction was monitored by likened to that of a “basketball net”. The “hoop” is oval EPR spectroscopy, employing a variety of reaction conwith cross “hoop” Ni-Ni distances of 5.325 (Nil-Nil’), ditions, solvents, and stoichiometries. In all cases, a signal 5.455 (Ni2-.N2’), and 6.644 A (Ni3-Ni3’). The “net” is attributable to 2 was seen to rapidly diminish in intensity comprised of the pseudo-square-planar coordination with time. Typically, within 1 h of reagent mixing, the spheres of the Ni atoms, each containing four sulfur atoms. solutions showed no EPR signal. On standing, black blocks The “net” is woven together by two methanethiolato groups bridging the Ni centers. Related Ni thiolate oli(37)Prout, K.;Critchley, S.R.; Rees, G. V. Acta Crystallogr., Sect. B gomers have been reported by the research groups of 1974, B30, 2305. Dahl,4l Dance,43and other^.^.^^ (38)Daran,J. C.; Meunier, B.; Prout, K. Acta Crystallogr., Sect. B

1

1979, B35, 1709.

(39)Ortiz, J. V. J. Am. Chem. SOC.1986, 108, 550. (40)White, G.S.;Wark,T.A.;Tse, J. S.;Stephan, D.W., unpublished results, 1989.

(41)Woodward,P.;Dahl,L. F.; Abel, E. W.;Crosse, B. C. J. Am.

Chem. SOC.1965,87, 5252.

Organometallics 1989,8, 2843-2850 The mechanism of formation of 6 from the reaction of 2 with Ni(COD), is not known. However, it is noteworthy that in the related reaction involving of Cp,V(SPh), and [Cp3Ni2][BF,], redox chemistry is accompanied by ligand transfer, yielding [Cp2V][BF,] and [CpNi(r-SPh)],. Isolation of 3 suggests that the initial step in the reaction may be coordination of 2 to Ni. Although the V byproduct is not isolated or characterized in this reaction, the isolation of a Ni(I1) product from the reaction suggests the V(1V) dithiolate 2 is reduced to a V(II1) species. These data suggest that the formation of the Ni(I1) product 6 may proceed via two inner-sphere, one-electron transfers from Ni to V, which are accommodated by the formation of a VzNi intermediate analogous to 3. (42)Darensbourg, M. Y.;Silva, R.; Reibenspies, J.; Prout, C. K. Organometallics 1989,8,1315. (43)Dance, I. G.; Scudder, M. L.; Secomb, R. Inorg. Chem. 1985,24, 1201. (44)Gould, R. 0.; Harding, M. M. J. Chem. SOC. A 1970,875. (45)Gaete, W.; Ros, J.; Solans, X.; Font-Altaba, M.; Brianso, J. L. Inorg. Chem. 1984,23,39.

2843

Summary Complexes 1 and 2 have been prepared and characterized. In reactions with Ni(COD)2, use of 1 affords the heterobimetallic complex 3. The structural data for 3 are consistent with the presence of a dative bond between the dl0 Ni(0) center and the do Ti(1V) metal centers. In contrast, reaction of 2 with Ni(COD),, results in electron and ligand transfer affording the hexameric Ni(I1) species 6. It is suggested that the formation of 6 proceeds through an VzNi analogue of 3. In a subsequent paper, we will describe a series of stable V(1V) heterobimetallics of the form [Cp2V(p-SR)2CuPR3]+.36 Acknowledgment. Financial support from NSERC of Canada is gratefully acknowledged. The authors of ref 42 are thanked for a communication of results prior to publication. Supplementary Material Available: Tables of thermal and hydrogen atom parameters (3 pages); listings of values of lOF, and lOF, (18 pages). Ordering information is given on any current masthead page.

Formal Transfers of Hydride from Carbon-Hydrogen Bonds. Synthesis, Structure, and Reactions of [Cp(CO),FeCH,]&H Michio Kobayashi and James D. Wuest" Gpartement de Chimie, Universit6 de Montrhi, Montkai, Ougbec, H3C 3 7 Canada Received June 26, 1989

The reaction of Cp(CO),FeNa with (CH3S020CH2)3CH(4) provided [Cp(C0)zFeCH2]3CH(3) in 50% yield. Thermal decomposition of compound 3 occurred rapidly in solution at 25 O C and produced approximately equimolar amounts of [Cp(CO),Fe], (5) and dicarbonyl(cyclopentadienyl)(cyclopropylmethyl)iron (6). These products presumably result from decarbonylation of compound 3, formation of carbonyl-bridged intermediate 8, and reductive elimination. The reaction of compound 3 with 2 equiv of Ph3C+PF{ yielded the Cp(CO),Fe+complex 11 of Cp(C0),FeCH2CH2CH=CH2and negligible amounts of triphenylmethane. Ph&+ may accept an electron from compound 3, triggering loss of Cp(CO),Fe*and a shift of Cp(C0)2FeCH2 that converts the isobutyl skeleton of the starting material into the n-butyl skeleton of product 11. Irradiation of compound 3 at 350 nm produced [Cp(CO),FeIz (5) and an exo/endo mixture of carbonyl(cyc1opentadienyl)(q3-2-methyl-2-propenyl)iron(34). These products appear to result from decarbonylation, formation of carbonyl-bridged intermediate 8, further decarbonylation, formation of iron hydride 33 by @-elimination,reductive elimination, and further irradiation of dicarbonyl(cyclopentadieny1) (Zmethyl2-propeny1)iron (2 1). Carbon-hydrogen bonds act as formal donors of hydride in many well-known redox reactions, including enzymatic reductions involving the coenzyme NADH, Cannizzaro reactions, and Meerwein-Ponndorf-Verley reductions. The subdued reactivity of these bonds is a distinct advantage since it allows a reducible substrate to be recognized and oriented by a receptor before the transfer of hydride takes place. Ordinary carbon-hydrogen bonds are not reactive enough to be useful, but those activated by adjacent lone pairs or carbon-metal bonds are very good formal donors of hydride. For example, tris[ (triphenylstanny1)methyllmethane (1) contains a carbon-hydrogen SnPh,

+P S h an ,

f,

F+cP:oe-)( \Ph

Ph >Lin-S-?

F~(CO):CP

-S SnPh,

1 -

Fe(C0XCp

Ph

-2

in high yie1d.l" Similar carbon-hydrogen bonds constrained to be antiperiplanar to several carbon-metal bonds are even more reactive formal donors of hydride. For example, the central carbon-hydrogen bond of stannaadamantane 2 is weaker than typical tin-hydrogen bonds? allowing compound 2 to reduce activated halides to the corresponding hydrocarbons.lc Since related compounds containing more electropositive metals like iron promised to be even more reactive formal donors of hydride, we decided to synthesize [Cp(CO),FeCH2l3CH(3)3 and study its reactions. After extensive experimentation, we found that compound 3 could be prepared efficiently by treating a solution

-3

bond activated by adjacent carbon-tin bonds, and it is therefore able to reduce Ph3C+PF6-to triphenylmethane 0276-7333/89/2308-2843$01.50/0

(1)(a) Ducharme, Y.;Latour, S.; Wuest, J. D. Organometallics 1984, 3,208-211. (b) Beauchamp, A. L.; Latour, S.; Olivier, M. J.; Wuest, J. D. J. Oganomet. Chem. 1983,254,283-291.(c) Ducharme, Y.;Latour, S.; Wuest, J. D. J.Am. Chem. SOC. 1984,106,1499-1500. Beauchamp, A. L.;Latour, S.; Olivier, M. J.; Wuest, J. D. Ibid. 1983,105,7778-7780. (2)Burkey, T.J.; Majewski, M.; Griller, D. J. Am. Chem. SOC.1986, 108,2218-2221. Dewar, M. J. S.; Grady, G.L. Organometallics 1985,4, 1327-1329. (3) Cp = ~6-2,4-cyclopentadien-l-yl.

0 1989 American Chemical Society