Dinuclear iminophenoxide copper complexes in rac-lactide polymerisation

Abstract

Dinuclear bis(R′-(R′′-iminomethyl)phenoxide) copper complexes L₂Cu₂(μ-OR)₂ were prepared from the reaction of copper methoxide with ROH and LH (ROH = dimethylaminoethanol or pyridylmethanol, R′ = H, 4,6-tBu, 1,3-Cl, R′′ = benzyl, cyclohexyl, diphenylmethyl and 2,6-dimethylphenyl). Preparation was complicated by formation of homoleptic L₂Cu and only 9 of the 24 possible combinations could be prepared. All complexes were characterized by single crystal X-ray diffraction studies and crystallized as dinuclear penta-coordinated complexes. Homoleptic complexes L₂Cu were inactive in lactide polymerization at room temperature. Most heteroleptic complexes showed modest to good activities with full conversion in less than 6 h at room temperature. Complexes with R′ = H showed poor molecular weight control, complexes with R′ = Cl were inactive in polymerization. In pyridylmethoxide-containing complexes, only one alkoxide initiated chain growth. All complexes produced atactic polymer.