Flash Communication: Reactivity of Bis(phosphine) Ligands with Dicobalt Octacarbonyl

A series of bis-(phosphine) cobalt carbonyl complexes were prepared and investigated in situ using cyclic voltammetry, ¹H, ³¹P, and ⁵⁹Co NMR spectroscopy (including DOSY), and IR spectroscopy. X-ray diffraction analysis on isolated single crystals confirmed that complex speciation was highly dependent on the nature of the bis-(phosphine) and ligand-to-metal stoichiometry. Reactions of [Co₂(CO)₈] with 1,2-bis-(dicyclohexylphosphino)-ethane (DCyPE) and 1,2-bis-(diphenylphosphino)-benzene (DPPBz) led to disproportionation of the precursor, affording cationic κ ²-Co-(I) bis-(phosphine) complexes with Co-(-I) tetracarbonyl cobaltate counteranions. In contrast, ferrocenyl bis-(phosphine) ligands 1,1'-bis-(diphenylphosphino)-ferrocene (DPPF), 1,1'-bis-(di-isopropylphosphino)-ferrocene (DⁱPrPF), and 1,1'-bis-(dicyclohexylphosphino)-ferrocene (DCyPF), displayed different reactivity. DⁱPrPF and DCyPF appeared to form polymeric species at 1:1 ligand-to-metal ratios but favored the formation of discrete neutral dinuclear complexes of the type [(μ²-L)-Co₂(CO)₆] when 0.5 equiv of ligand was employed. Reaction of [Co₂(CO)₈] with DPPF yielded a significantly larger molecular assembly. Single-crystal X-ray diffraction revealed an unprecedented metallocyclic structure comprising six cobalt tricarbonyl centers interconnected by four bridging DPPF ligands.