Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 111. Protonation of the salts [NEt₄][M(CR)(CO)₂(η^x-C₂B_nH_nMe₂)](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.