Alkylidyne(carbaborane) complexes of the Group 6 metals. Part 4. Formation of unsaturated dimetal species, including ‘reverse’ polytopal isomerisation, and reactions with trimethylphosphine

Abstract

Treatment of a mixture of [NEt4][W(CMe)(CO)2(η5-7,8-C2B9H9-7,8-Me2)] and [W(CMe)(CO)2(η-C5H5)] with HBF4·Et2O in CH2Cl2 at –78 °C affords the dimetal complex [W2(µ-CMe)(CO)3(η-C5H5){η5-7,8-C2B9H8-10-Et-7,8-Me2}], which with PMe3 gives [W2(µ-CMe)(CO)3(PMe3)(η-C5H5){η5-7,8-C2B9H8-10-Et-7,8-Me2}]. Mixtures of the salts [X][WI(CO)3{η5-2,8-C2B9H8-10-(CH2R)-2,8-Me2}](X = NMe3Ph or AsPh4, R = C6H4Me-4) and the compounds [M(CR)(CO)2(η-C5H5)](M = W or Mo) in CH2Cl2 react with AgBF4 to yield the dimetal complexes [MW(µ-CR)(CO)3(η-C5H5){η5-2,8-C2B9H8-10-(CH2C6H4Me-4)-2,8-Me2}] and [W2(µ-CC6H4Me-4)(CO)4(η-C5H5){η5-2,8-C2B9H8-10-(CH2C6H4Me-4)-2,8-Me2}]. The corresponding reaction between a mixture of [AsPh4][WI(CO)3{η5-2,8-C2B9H8-10-(CH2R)-2,8-Me2}](R = C6H4Me-4) and [W(CMe)(CO)2(η-C5H5)], in the presence of TIBF4, affords equal amounts of the two isomers [W2(µ-CMe)(CO)3-(η-C5H5){η52,8-C2B9H8-10-(CH2R)-2,8-Me2}] and [W2(µ-CMe)(CO)3(η-C5H5){η5-7,8-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(µ-CMe)(CO)3(η-C5H5){η5-7,8-C2B9H8-10-(CH2R)-7,8-Me2}](R = Me or C6H4Me-4) from reactions of AgBF4 with mixtures of [X][WI(CO)3{η5-2,8-C2B9H8-10-(CH2R)-2,8-Me2}] and [W(CMe)(CO)2-(η-C5H5)]. Some reactions of the dimetal compounds containing η5-C2B9H8-10-(CH2R)-Me2 groups with PMe3 have been studied, and the crystal structure of [W2(µ-CC6H4Me-4)(CO)3(PMe3)(η-C5H5){η5-2,8-C2B9H8-10-(CH2C6H4Me-4)-2,8-Me2}] has been determined by X-ray crystallography. The W–W bond [2.798(1)Å] is spanned essentially symmetrically by the p-tolylmethylidyne group [µ-C–W (average) 2.03 Å]. One W atom carries the C5H5 ring, a CO group and the PMe3 ligand [W–P 2.478(3)Å]. 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 (1H, 13C-{1H}, 11B-{1H}, 11B, and 31P-{1H}) for the new compounds are reported and discussed.