Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 58. Some reactions of the compounds [MW(µ-CC6H4Me-4)(CO)3(η5-C9H7)(η5-C2B9H9Me2)](M = Mo or W); crystal structures of the complexes [W2(µ-CC6H4Me-4)(CO)2(L)(η5-C9H7)(η5-C2B9H9Me2)][L = N2C(C6H4Me-4)2 or O]