Bimetallic Zinc Catalysts for Ring-Opening Copolymerization Processes

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 L-1-L-3 were reacted with two equivalents of zinc acetate to afford the dinuclear zinc complexes [{Zn(kappa(3)-bpzappe)}(mu-O2CCH3)(3)-{Zn(HO2CCH3)}] (1), [{Zn(kappa(3)-bpzbdmape)}(mu-O2CCH3)(3)-{Zn(HO2CCH3)}] (2), and [{Zn(kappa(3)-bpzbdeape)}(mu-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.