Synthesis and structures of N-arylcyano-β-diketiminate zinc complexes and adducts and their application in ring‐opening polymerization of l-lactide

Abstract

Zinc amide complexes ZnL₁N(SiMe₃)₂, ZnL₂N(SiMe₃)₂ (1 and 2), their tris(pentafluorophenyl)borane adducts ZnL₁N(SiMe₃)₂·B(C₆F₅)₃ (3), ZnL₂N(SiMe₃)₂·2B(C₆F₅)₃ (4), pentafluorophenyl zinc complex ZnL₁C₆F₅ (5) and its adduct ZnL₁C₆F₅·B(C₆F₅) (6) supported by N-arylcyano-β-diketiminate ligands, as well as bis-ligated Zn(L₂)₂ (7) were synthesized and characterized by NMR, IR, elemental analysis and X-ray diffraction. Zinc crystal structures of 1, 4, and 7 showed mononuclear complexes, while 2 and 5 were dimmers. ROP of L-lactide with zinc complexes and their B(C₆F₅)₃ adducts leads to generation of poly(L-LA) with high molecular weight and relatively narrow molecular weight distribution. The monomer conversion reached completion in 40 min only for zinc amide complex 1, while for other compounds it was necessary to use at least 5 hours to achieve significant polymerization yields. Coordination of the B(C₆F₅)₃ molecule close to the metal center blocks L-lactide insertion and thus decreases the activity of respective adducts in comparison with borane-free zinc complexes.