Cobalt Complexes Supported by cis-Macrocyclic Diphosphines: Synthesis, Reactivity, and Activity toward Coupling Carbon Dioxide and Ethylene

The coordination chemistry of cis-macrocyclic diphosphines readily accessed from white phosphorus was explored, with a focus on preparing and studying cobalt complexes. cis-1,6-Dicyclohexyl-3,4,8,9-tetramethyl-2,5,7,10-tetrahydro-1,6-DiPhospheCine, or Cy2–DPC (1), was primarily used as a model diphosphine. Cobalt­(II) dihalide diphosphine complexes such as (Cy2–DPC)­CoX2, X = Cl (2) and I (3), were prepared, and their reactivity toward a variety of reducing agents was studied. We were successful in preparing and structurally characterizing an unusual iodide-bridged cobalt­(I) dimer, [(Cy2–DPC)­CoI]2 (8). These cobalt complexes were also investigated as potential catalysts for the coupling of carbon dioxide and ethylene to produce acrylate, a valuable polymer precursor. Although not yet catalytic, the first examples of cobalt complexes capable of mediating this transformation are reported. Notably, the well-known commercial complex ClCo­(PPh3)3 was also found to be active in mediating acrylate production. As part of our mechanistic investigation, a pseudotetrahedral cobalt methyl acrylate complex, (Cy2–DPC)­CoI­(CH2CHCOOMe) (10), was prepared and structurally characterized.