Copper(II) complexes containing N′-aromatic group substituted N,N′,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)amines: Synthesis, structures, polymerization of methyl methacrylate and ring opening polymerization of rac-lactide

A series of Cu(II) complexes, [L_nCuCl₂] (L_n = L_A–L_F), supported by N′-aromatic-group-substituted N,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methylamine ligands have been synthesized. Variations of substituents at the ortho position of the aniline moiety influenced the solid-state structures of these complexes. The X-ray structures of [L_nCuCl₂] (L_n = L_A–L_C and L_F) revealed that ligands are coordinated in a N,N,N-tridentate fashion to Cu(II) center and adopted a distorted square-pyramidal geometry, while [L_DCuCl₂] with N,N-bidentate coordination adopts distorted tetrahedral geometry. These complexes were capable of polymerizing methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO), with [L_FCuCl₂] displaying the highest activity (2.81 × 10⁴ g PMMA (mol Cu)⁻¹h⁻¹). Regardless of ligand architecture, syndio-enriched PMMAs have been furnished with a slightly broader polydispersity index (PDI). Additionally, the in situ generated dimethyl derivatives, polymerized rac-LA and furnished PLA with mediocre heterotacticities at room temperature. Importantly, the catalytic efficiencies of the Cu(II) complexes studied have been found to be influenced by the steric and electronic properties of ligand.