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

Abstract

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 Cy 2 –DPC ( 1 ), was primarily used as a model diphosphine. Cobalt(II) dihalide diphosphine complexes such as (Cy 2 –DPC)CoX 2, 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, [(Cy 2 –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(PPh 3 ) 3 was also found to be active in mediating acrylate production. As part of our mechanistic investigation, a pseudotetrahedral cobalt methyl acrylate complex, (Cy 2 –DPC)CoI(CH 2 CHCOOMe) ( 10 ), was prepared and structurally characterized.