Synthesis, Structures, and Catalytic Activity of Homo‐ and Heteroleptic Ketoiminate Zinc Complexes in Lactide Polymerization

摘要

> The heteroleptic complex LZnEt [( 1 ); L = MeNacac = MeNC(Me)CHC(Me)O] containing the sterically less demanding N , O ‐chelating ketoiminate (MeNacac) ligand was synthesized by reaction of ZnEt ₂ with an equimolar amount of MeNacacH, whereas the reaction with two equivalents MeNacacH gave the homoleptic complex L ₂ Zn 5 . 1 reacts with ArOH (Ar = 2,6‐Me ₂ ‐Ph) with ethane elimination and formation of LZnOAr ( 2 ). Addition of the Lewis base dmap (dmap = 4‐dimethylamino pyridine) to 1 and 2 yielded the corresponding Lewis acid‐base adducts dmap‐Zn(L)Et 3 and dmap‐Zn(L)OAr 4 . Compounds 1 – 5 were characterized by heteronuclear NMR ( 1 H, 13 C) and IR spectroscopy, elemental analysis, and single‐crystal X‐ray diffraction ( 1 – 3 , 5 ). Their technical application as catalysts in ring‐opening polymerization (ROP) of rac ‐lactide in CD ₂ Cl ₂ or CDCl ₃ solutions at ambient temperature was investigated. 2 and 3 show the highest activities, whereas those of 1 and 5 are substantially lower. 2 and 3 polymerize rac ‐lactide (90?% conversion) within 140 ( 3 ) and 180 ( 2 ) minut