Bimetallic Zinc Catalysts for Ring-Opening Copolymerization Processes

Abstract

Novel bimetallic zinc acetate complexes supported by heteroscorpionate ligands have been developed for the ring-opening copolymerization of cyclohexene oxide and CO₂ and the terpolymerization of cyclohexene oxide, phthalic anhydride, and CO₂. Heteroscorpionate ligands precursors L₁–L₃ were reacted with two equivalents of zinc acetate to afford the dinuclear zinc complexes [{Zn(κ³-bpzappe)}(μ-O₂CCH₃)₃-{Zn(HO₂CCH₃)}] (1), [{Zn(κ³-bpzbdmape)}(μ-O₂CCH₃)₃-{Zn(HO₂CCH₃)}] (2), and [{Zn(κ³-bpzbdeape)}(μ-O₂CCH₃)₃{Zn(HO₂CCH₃)}] (3) in excellent yields. The molecular structure of these compounds was determined spectroscopically and confirmed by X-ray diffraction analysis. Zinc acetate complexes 1–3 were screened as catalysts for the copolymerization of cyclohexene oxide and CO₂ to produce poly(cyclohexene)carbonate, and complex 3 was found to be the most active catalyst for this process in the absence of a cocatalyst. Furthermore, the terpolymerization of cyclohexene oxide, phthalic anhydride, and CO₂ was studied using the combination of complex 3 and 4-dimethylaminopyridine as catalyst system yielding the corresponding polyester-polycarbonate materials.