Ligand substitution in the mixed-metal cluster PhCCo2Ni(CO)6Cp by 2,3-bis(diphenylphosphino)maleic anhydride (bma): An intimate picture involving the stepwise conversion of the trinuclear cluster PhCCo2Ni(CO)4(η2-bma)Cp to the mononuclear compound CpNi[P

Thermolysis of the tetrahedral cluster PhCCo2Ni(CO)6Cp (1) with the diphosphine ligand 2,3-bis(diphenylphosphino)maleic anhydride (bma) furnishes the cobalt-bridged cluster PhCCo2Ni(CO)4(η2-bma)Cp (2). Thermolysis of 2 proceeds in a stepwise fashion to give the clusters PhCCo2Ni(CO)3(μ,η2-bma)Cp (3), and Co2Ni(CO)4Cp[μ2,η2,η1-C(Ph)CC(PPh2)C(O)OC(O)](μ2-PPh2) (4), and the mononuclear nickel complex CpNi[PPh2CPhCC(PPh2)C(O)OC(O)] (5). These compounds have been fully characterized in solution by IR and NMR spectroscopies, and the molecular structures of clusters 2-5 have been crystallographically determined.