Diphosphine Substitution and Carbyne Ligand Transfer in the Reaction of 2,3-Bis(diphenylphosphino)maleic Anhydride (bma) with the Methylidyne-capped Clusters HCCo2MCp(CO)8 (where M=Mo, W): Synthesis and X-ray Diffraction Structures of the Vinylidene-bridged Clusters Co2MCp(CO)6[μ–C=C(H)CH2C(PPh2)C(PPh2)C(O)OC(O)] |