Mono- and dinuclear copper complexes coordinated on NNO-tridentate Schiff-base derivatives for copolymerization of cyclohexene oxide and cyclic anhydrides

Abstract

A series of bimetallic penta-coordinated copper complexes [Lⁿ₂Cu₂(OAc)₂] (1, 3–7), a mononuclear tetra-coordinated copper complex [LⁿCu(OAc)] (8 and 9), and a penta-coordinated copper complex [L²Cu(OAc)(H₂O)] (10) were prepared by the reaction of Cu(OAc)₂·H₂O with a variety of NNO-tridentate Schiff-base ligands (L¹-H–L⁹-H) in refluxing 95% ethanol, respectively. However, a dinuclear copper complex [(L²)₂Cu₂(OAc)₂] (2) can be obtained from the treatment of L²-H with a stoichiometric amount of anhydrous Cu(OAc)₂ in refluxing absolute EtOH under a dry nitrogen atmosphere. All of these copper complexes are active for the alternating copolymerization of cyclohexene oxide and cyclic anhydride, affording polyesters with moderate polydispersity. In particular, dinuclear copper complexes 1 and 2 performed satisfactorily to produce polyesters with controllable molecular weights and high ester linkages. This is the first example of well-defined copper acetate catalysts active for the copolymerization of cyclohexene oxide-phthalic anhydride or cyclohexene oxide-succinic anhydride which may be advantageous in terms of obviating the use of co-catalysts and low cost as well as an effective copolymerization for the formation of biodegradable polyesters in a controlled fashion.