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.