ALKYLIDYNE(CARBABORANE) COMPLEXES OF THE GROUP-6 METALS .4. FORMATION OF UNSATURATED DIMETAL SPECIES, INCLUDING REVERSE POLYTOPAL ISOMERIZATION, AND REACTIONS WITH TRIMETHYLPHOSPHINE

Treatment of a mixture of [NEt4][W( = CMe)(CO)2(eta(5)-7,8-C2B9H9-7,8-Me2)] and [W( = CMe)(CO)2(eta-C5H5)] with HBF4.Et2O in CH2Cl2 at -78-degrees-C affords the dimetal complex [W2(mu-CMe)(CO)3(eta-C5H5){eta(5)-7,8-C2B9H8-10-Et-7,8-Me2}], which with PMe3 gives [W2(mu-CMe)(CO)3(PMe3)(eta-C5H5){eta(5)-7,8-C2B9H8-10-Et-7,8-Me2}]. Mixtures of the salts [X][WI(CO)3{eta(5)-2,8-C2B9H8-10-(CH2R)-2,8-Me2}] (X = NMe3Ph or AsPh4, R = C6H4Me-4) and the compounds [M( = CR)(CO)2(eta-C5H5)] (M = W or Mo) in CH2Cl2 react with AgBF4 to yield the dimetal complexes [MW(mu-CR)(CO)3(eta-C5H5){eta(5)-2,8-C2B9H8-10-(CH2C6H4Me-4)-2,8-Me2}] and [W2(mu-CC6H4Me-4)(CO)4(eta-C5H5){eta(5)-2,8-C2B9H8-10-(CH2C6H4Me-4)-2,8-Me2}]. The corresponding reaction between a mixture of [AsPh4][WI(CO)3{eta(5)-2,8-C2B9H8-10-(CH2R)-2,8-Me2}] (R = C6H4Me-4) and [W( = CMe)(CO)2-(eta-C5H5)], in the presence of TIBF4, affords equal amounts of the two isomers [W2(mu-CMe)(CO)3-(eta-C5H5){eta(5)-2,8-C2B9H8-10-(CH2R)-2,8-Me2}] and [W2(mu-CMe)(CO)3(eta-C5H5){eta(5)-7,8-C2B9H8-10-(CH2R)-7,8-Me2}]. The latter product is the result of a polytopal rearrangement of the cage CMe groups in the precursor. This isomerisation also occurs in the formation of the complexes [W2-(mu-CMe)(CO)3(eta-C5H5){eta(5)-7,8-C2B9H8-10-(CH2R)-7,8-Me2}] (R = Me or C6H4Me-4) from reactions of AgBF4 with mixtures of [X][WI(CO)3{eta(5)-2,8-C2B9H8-10-(CH2R)-2,8-Me2}] and [W( = CMe)(CO)2-(eta-C5H5)]. Some reactions of the dimetal compounds containing eta(5)-C2B9H8-10-(CH2R)-Me2 groups with PMe3 have been studied, and the crystal structure of [W2(mu-CC6H4Me-4)(CO)3(PMe3)(eta-C5H5)-{eta(5)-2,8-C2B9H8-10-(CH2C6H4Me-4)-2,8-Me2}] has been determined by X-ray crystallography. The W-W bond [2.798(1) angstrom] is spanned essentially symmetrically by the p-tolymethylidyne group [mu-C-W (average) 2.03 angstrom]. One W atom carries the C5H5 ring, a CO group and the PMe3 ligand [W-P 2.478(3) angstrom]. The other W atom is co-ordinated by two CO groups and a nido-2,8-C2B9H8-10-(CH2C6H4Me-4)-2,8-Me2 icosahedral fragment. The NMR data (H-1, C-13-{H-1}, B-11-{H-1}, B-11, and P-31-{H-1}) for the new compounds are reported and discussed.