Ligand substitution in HC(O)CCo3(CO)9 with 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd): Diphosphine ligand fluxionality, decarbonylation of the formyl moiety and competitive P–Ph bond cleavage reactivity

The reaction of the formyl-capped cluster HC(O)CCo3(CO)9 (1) with the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) in the presence of added Me3NO leads to the production of the disubstituted cluster HC(O)CCo3(CO)7(bpcd) (2). Thermolysis of 2 in toluene at 60 °C gives the methylidyne-capped cluster HCCo3(CO)7(bpcd) (4) and the phosphido-bridged cluster Co3(CO)7[μ2,η2,η1-P(Ph)Cdouble bond; length as m-dashC(PPh2)C(O)CH2C(O)] (5). Cluster 4 has been independently prepared from HCCo3(CO)9 and bpcd and shown to serve as the precursor to 5. The new clusters 2, 4, and 5 have been isolated and characterized in solution by IR and NMR (1H and 31P) spectroscopies and their solid-state structures have been established by X-ray diffraction analyses. Both clusters 2 and 4 contain 48e- and exhibit triangular Co3 cores with a chelating and bridging bpcd ligand in the solid state, respectively. The structure of 5 provides unequivocal support for the loss of the methylidyne capping ligand and P–Ph bond cleavage attendant in the activation of 4 and confirms the presence of the face capping seven-electron μ2,η2,η1-P(Ph)Cdouble bond; length as m-dashC(PPh2)C(O)CH2C(O) ligand in the final product. The fluxionality displayed by the bpcd ligand in clusters 2 and 4 and the decarbonylation behavior of the formyl moiety in the former cluster are discussed relative to related alkylidyne-capped Co3 derivatives.