Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 111. Protonation of the salts [NEt4][M(CR)(CO)2(ηx-C2BnHnMe2)](M = Mo or W; R = Me or C6H4Me-4; x= 5, n= 9; x= 6, n= 10) in the presence of the alkylidynemetal compounds [M(CR)(CO)2(η-C5H5)]; crystal structures of [W2(µ-CMe)(CO)3{η5-C2B9H8(CH2C6H4Me-4)Me2}(η-C5H5)], [W2(µ-CC6H4Me-4)(CO)3(η5-C2B9H9Me2)(η-C5H5)] and [MoW(µ-CC6H4Me-4)(CO)2(PMe3)(η6-C2B10H10Me2)(η5-C5H5)]

Abstract

Treatment of mixtures of [NEt₄][W(CC₆H₄Me-4)(CO)₂(η⁵-C₂B₉H₉Me₂)] and [M(CR)(CO)₂(η-C₅H₅)](M = W, R = Me; M = Mo, R = C₆H₄Me-4) in CH₂Cl₂ at –78 °C with HBF₄·Et₂O affords, respectively, the complexes [MW(µ-CR)(CO)₃{η⁵-C₂B₉H₈(CH₂C₆H₄Me-4)Me₂}(η⁵-C₅H₅)]. The structure of the ditungsten compound was determined by X-ray crystallography. The W–W bond [2.651(1)Å] is spanned essentially symmetrically by the ethylidyne group [µ-C–W 1.95(1) and 2.03(1)Å]. One W atom is co-ordinated by two CO groups and the open pentagonal face of a nido-icosahedral C₂B₉ cage. A boron atom in the β site of the [graphic omitted] face carries a CH₂C₆H₄Me-4 substituent, and a BH group in the face α to the carbon atoms forms an exopolyhedral B–H⇀W bond to the other tungsten, which carries a CO molecule and the C₅H₅ ring. In contrast, protonation of a mixture of [NEt₄][W(CC₆H₄Me-4)(CO)₂(η⁵-C₂B₉H₉Me₂)] and [W(CC₆H₄Me-4)(CO)₂(η-C₅H₅)] yields the complex. [W₂(µ-CC₆H₄Me-4)(CO)₂(η⁵-C₂B₉H₉Me₂)(η-C₅H₅)]. The latter in toluene at 80 °C undergoes a polytopal rearrangement affording an isomer in which the nido-icosahedral C₂B₉H₉Me₂ fragment has a 7,9-C₂ rather than the 7,8-C₂ configuration present in the [C₂B₉H₉Me₂]^2– dianion in the precursor. This was confirmed by an X-ray diffraction study on the 7,9 isomer, which was also obtained by treating a mixture of [NEt₄][W(CC₆H₄Me-4)(CO)₂(η⁶-C₂B₁₀H₁₀Me₂)] and [W(CC₆H₄Me-4)(CO)₂(η-C₅H₅)] in CH₂Cl₂ at –78 °C with HBF₄·Et₂O. This is a remarkable 13- to 12-vertex cage degradation process. In both isomers of [W₂(µ-CC₆H₄Me-4)(CO)₃(η⁵-C₂B₉H₉Me₂)(η-C₅H₅)] the metal–metal bonds are spanned by B–H⇀W three-centre two-electron bonds as well as p-tolymethylidyne groups. Protonation of a mixture of [NEt₄][W(CC₆H₄Me-4)(CO)₂(η⁶-C₂B₁₀H₁₀Me₂)] and [Mo(CC₆H₄Me-4)(CO)₂(η-C₅H₅)] gave two dimetal compounds: [MoW(µ-CC₆H₄Me-4)(CO)₃(η⁵-7,9-C₂B₉H₉Me₂)(η-C₅H₅)] and [MoW(µ-CC₆H₄Me-4)(CO)₃(η⁶-C₂B₁₀H₁₀Me₂)(η-C₅H₅)]. Treatment of the latter with PMe₃ yields [MoW(µ-CC₆H₄Me-4)(CO)₂(PMe₃)(η⁶-C₂B₁₀H₁₀Me₂)(η-C₅H₅)], the structure of which has been determined by X-ray diffraction. The Mo–W bond [2.702(1)Å] is bridged on one side by the CC₆H₄Me-4 group [µ-C–Mo 1.94(1), µ-C–W 2.10(1)Å] and on the other by the C₂B₁₀H₁₀Me₂ cage. The latter is η⁶ co-ordinated to the W atom via an open [graphic omitted]B face, and this metal atom also carries two CO ligands. The boron atom [graphic omitted]B in the face of the cage which is in a β site with respect to the carbons forms an exopolyhedral B–H⇀Mo bond across the Mo–W bond. The Mo atom is co-ordinated by the PMe₃ ligand [Mo–P 2.496(4)Å] and the C₅H₅ ring. The NMR data (¹H, ¹³C-{¹H}, ¹¹B-{¹H}, ³¹P-{¹H}) for the new complexes are reported and discussed.