ACTIVATION OF CARBON DIOXIDE BY TRANSITION METAL COMPLEXES

Program year: 1989/1990Digitized from print original stored in HDRGroup 6 metal anionic complexes, (CO)₅M(O₂CR)⁻ (M = Cr, Mo, W; R = Me, OPh , were investigated for potential catalytic properties that would mediate a copolymer synthesis. Copolymers made of alternating carbon dioxide and epoxides have been activated by various reported organozinc complexes. A similar group 6 metal species was sought as a probe for the mechanistic features of a proposed catalytic cycle. At present, details about the mechanisms that facilitate carbon dioxide and epoxide copolymerization are poorly understood. In a proposed mechanistic scheme for a copolymer synthesis of CO₂ and epoxides, the activation of the CO₂ by group 6 metal complexes represents a very well-documented and important step, applicable in the chain propagation. The epoxide insertion, however, remains an elusive detail to the complete copolymer cycle. Two group 6 anionic species, (CO)₅M(O₂CCH₃)⁻, 1, and (CO)₅M(O₂COPh)⁻, 5, represent CO₂ insertion products that were investigated for potential catalytic activity toward propylene oxide