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)]