Phosphine Ligand Attack at Both the Methylidyne Cap and the CpNi Center in HCCo2NiCp(CO)6by 2,3-Bis(diphenylphosphino)maleic Anhydride (bma): P−C Bond Cleavage Reactivity, Kinetics, and X-ray Structures of the Zwitterionic Clusters Co2NiCp(CO)4(μ-CO)[μ2,η2,η1-C(H)PPh2CC(PPh2)C(O)OC(O)] and Co2NiCp(CO)4[μ2,η2,σ-C(H)PPh2CCC(O)OC(O)](μ2-PPh2)

Abstract

Thermolysis of the hydrogen-capped cluster HCCo2NiCp(CO)6 (1) with the redox-active diphosphine 2,3-bis(diphenylphosphino)maleic anhydride (bma) in DCE at ca. 80 °C affords the zwitterionic cluster (2) as the first observable product. Cluster 2 is not stable and transforms into the phosphido-bridged cluster (3). Both clusters 2 and 3 have been isolated and characterized in solution by IR and 31P NMR spectroscopies, and the solid-state structures of both 2 and 3 have been determined by X-ray crystallography. Cluster 2 exhibits an open Co2Ni core having one Co−Co and Co−Ni bond. The bma ligand is attached to the hydrocarbyl and CpNi moieties via the PPh2 groups, and one of the Co centers is tethered to the π bond of the bma ligand. The opened Co2Ni core of cluster 3 is structurally similar to 2 and consists of a μ2-PPh2 ligand that spans the Co−Co bond and a Ni−C σ bond resulting from the formal coupling of the maleic anhydride residue with the CpNi moiety. The reaction involving the conversion of 2 to 3 wa...