7111
J . Am. Chem. Soc. 1980,102, 7 11 1-7 113
Metal-Metal Bonded Complexes of the Early Transition Metals: Synthesis of a Binuclear Tantalum(II1) Trimethylphosphine Complex and Its Reactions with Hydrogen and Ethylene Sir: Binuclear complexes of tantalum(II1) are very rare, and the only well-characterized dimers are the tantalum(II1) halide adducts with tetrahydrothiophene (THT).' An X-ray crystallographic study of Ta2Br6(THT),, la, revealed the metal-metal bonded confacial bioctahedral structure.* The Ta-Ta separation
n
la
of 2.710(2) A has been interpreted as a formal metal-metal double bond on the basis of molecular orbital arguments. The chloro analogue of la is exceptionally reactive in the presence of organic substrates with triple bonds., Alkyl cyanides are reductively coupled by Ta2C16(THT)3,lb, with concomitant oxidation of the metal atoms (eq l), and simple alkynes are catalytically polymlb
+
RCN
-
CI3(RCN)zTa=N-C
/R
>CR
N=Ta(RCN12C13
(1)
erized to substituted arenes by l b . We report here a further elaboration of the noncyclopentadienyl chemistry of tantalum(II1) which has led to the structural characterization of two interesting binuclear tantalum complexes. Reduction of tantalum pentachloride in the presence of 2-2.5 equiv of trimethylphosphine (eq 2) provides an air-sensitive
+ 2Na/Hg + PMe,
PhCH,
Ta2C16(PMe3)4+ 2NaC1 (2) burgundy red diamagnetic solid, 3, in -75% yield. One recrystallization from toluene at -40 'C provided an analytically pure ample.^ 2 is dimeric in toluene, and its 31P{1H) NMR spectrumS shows two singlets (each of area one) at 6 -3 1.O and -57.1. These data led us to postulate an edge-sharing bioctahedral structure wherein two PMe, ligands adopt axial positions on one tantalum with the remaining phosphines in terminal equatorial positions on the second tantalum. This was confirmed in a single-crystal X-ray structure determination (vide infra). Further reduction of the isolated 3 with sodium amalgam in toluene or T H F has been attempted. Reduction, as evidenced by the formation of sodium chloride, does take place, but a mixture of products is formed (by 31PNMR) which we have not, as yet, been able to separate.6 Crystals of 2 were grown from concentrated toluene solutions, carefully layered with methylcyclohexane at -40 "C, and its structure was determined from diffraction data collected at -1 70 'C.' The molecular geometry with selected bond distances and angles is shown in Figure 1. The molecule consists of two TaCIS
(1) Templeton, J. L.; McCarley, R. E. Inorg. Chem. 1978, 1 7 , 2293. (2) Templeton, J. L.; Dorman, W. C.; Clardy, J. C.; McCarley, R. E. Inorg. Chem. 1978, 17, 1263. (3) Cotton, F. A.; Hall, W. T. J . Am. Chem. SOC.1979, 101, 5094. (4) Elemental analyses and molecular weight measurements were performed by Galbraith Laboratories, Knoxville, Tn. Anal. Calcd for Ta2Cl6P4CI2Hx:C, 16.40; H, 4.13; C1, 24.20; mol wt, 879. Found: C, 16.53; H, 4.12; C1, 24.42; mol wt, 876. (5) These 31P NMR measurements were recorded at 36.20 MHz on a JEOL FX90Q. Chemical shifts (6) are in ppm from external H3P04. Shifts are negative for lines upfield of HIPOI. Free PMea in benzene-d6 appears at 6 -63.3. (6) (a) It is interesting to note that sodium amalgam reductiodb of TaCIS in the presence of 1,2-bis(dimethylphosphino)ethane (dmpe) do nof provide Ta(II1) complexes. Only paramagnetic TaC14(dmpe) or TaC12(dmpe)2can be isolated from the reaction mixtures. (b) Datta, S.; Wreford, S. S. Inorg. Chem. 1977, 16, 1134.
0002-7863/80/1502-7111$01.00/0
i c Figure 1. ORTEP drawing of the structure of Ta$&(PMe3)4. Selected data not presented in the text: T a ( l ) C 1 ( 3 ) , 2.477 (3) A; Ta(l)-C1(5), 2.398 (3) A; Ta(1)-P(9), 2.666 (4) A; Ta(2)-C1(3), 2.427 (3) A; Ta(2)-C1(7), 2.472 (3) A; Ta(2)-P(1 l), 2.598 (4) A; P(9)-Ta(l)-P(IO), 98.9 (I)"; C1(7)-Ta(2)-C1(8), 86.6 (1)'; C1(3)-Ta(l)C1(4), 111.1 (1)'; and C1(3)-Ta(2)-C1(4), 114.1 (I)".
somewhat distorted octahedra sharing a common edge. The M-M separation in this dZ-d2dimer is 2.721 (1) (1) A, only slightly longer than that found in la. The only other structurally characterized metal complex with an overall geometry and ligand stereochemistry similar to 2 is the d3A3dimer, W2C16(pyridine)4 (3)? Comparison of these two structures is pertinent (vide infra) and reveals the following trends (tantalum data given first): (1) the metal-bridge chlorine-metal angle, Ob, increases from 67.4 (1)' to 69.8 (2)'; (2) the M-M separation increases from 2.721 (1) A to 2.737 (3) A; (3) the M(l)-M(2)-Lax,a, (L = PMe3, CSHSN)angle decreases from 97.6 (1)' to 94.1 (7)', and the M(2)-M(l)
