Synthesis of the chiral tetrahedral clusters RCCo2NiCp(CO)4(bmf) (R = H, Ph) and thermally promoted diphosphine ligand activation: Regiospecific P–C bond scission and X-ray diffraction structure of Co2NiCp(CO)4[μ2,η2,η1-C(H)Cdouble bond; length as m-dashC

Controlled thermolysis of the mixed-metal clusters RCCo2NiCp(CO)6 (R = H, Ph) with the chiral diphosphine ligand 3,4-bis(diphenylphosphino)-5-methoxy-2(5H)-furanone (bmf) leads to CO substitution and formation of the corresponding bmf-bridged clusters RCCo2NiCp(CO)4(bmf) (R = H, Ph). These clusters exist in solution as a non-interconverting mixture of diastereomers, as determined by NMR spectroscopy. Whereas the benzylidyne-capped cluster PhCCo2NiCp(CO)4(bmf) decomposes in 1,2-dichloroethane (DCE) during prolonged heating at 83 °C, thermolysis of HCCo2NiCp(CO)4(bmf) affords the new phosphido-bridged cluster Co2NiCp(CO)4[μ2,η2,η1-C(H)Cdouble bond; length as m-dashC(PPh2)C(O)OCH(OMe)](μ-PPh2) under the same conditions. This latter cluster has been isolated and characterized in solution by IR and NMR spectroscopies and the solid-state structure determined by X-ray diffraction analysis. The structural highlights for Co2NiCp(CO)4[μ2,η2,η1-C(H)Cdouble bond; length as m-dashC(PPh2)C(O)OCH(OMe)](μ-PPh2) include the regioselective cleavage of the P–C(furanone ring) bond, coupled with polyhedral opening of the Co2Ni core and attack on the CpNi center by the other phosphine moiety of the bmf ligand. The diastereoselectivity accompanying the formation of cluster Co2NiCp(CO)4[μ2,η2,η1-C(H)Cdouble bond; length as m-dashC(PPh2)C(O)OCH(OMe)](μ-PPh2) is discussed relative to steric effects within the cluster polyhedron.