Stereoselective polymerization of methyl methacrylate and rac-lactide mediated by iminomethylpyridine based Cu(ii) complexes

Abstract

Iminomethylpyridine based copper(II) complexes [L_nCuCl₂] (L_n = L_A, L_C–L_F) and [L_BCu(μ-Cl)Cl]₂ have been synthesized and characterized. [L_CCuCl₂] and [L_ECuCl₂] were identified to possess distorted square pyramidal geometries obtained via N,N′-bidentate coordination, whereas [L_FCuCl₂] showed N,N′,N′′-coordination of the corresponding ligand (L_F). [L_BCu(μ-Cl)Cl]₂ was found to be dimeric with a distorted square pyramidal geometry around the Cu(II) center. The catalytic properties of dimethyl derivatives, generated in situ, towards the ring opening polymerization (ROP) of rac-LA were investigated. All the complexes efficiently polymerized rac-LA and yielded heterotactic poly(lactide) (PLA) (P_r up to 0.88 at −25 °C). Further, these complexes could effectively polymerize methyl methacrylate (MMA) at 60 °C in the presence of modified methylaluminoxane (MMAO), to furnish syndio-enriched PMMA. The catalytic efficacies of synthesized complexes can be correlated to the suitable complexity of the substituents attached to the ligand architecture. Thus, both the steric and electronic properties as well as the orientation of the various substituents relative to the xy plane of the pyridyl moiety and metal center play an influential role in steering catalytic activities, whereas the selectivities remain unaffected.