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 ZnEt₂ with an equimolar amount of MeNacacH, whereas the reaction with two equivalents MeNacacH gave the homoleptic complex L₂Zn 5. 1 reacts with ArOH (Ar = 2,6‐Me₂‐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 (¹H, ¹³C) 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 CD₂Cl₂ or CDCl₃ 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) minutes, respectively. In contrast, 4 could only be investigated in bulk polymerization reactions due to its very poor solubility in common organic solvents. These studies proved that 4 is active in bulk polymerization, converting 93 % lactide to polylactide at 140 °C within 20 minutes.

Dedicated to Prof. Dr. K. Jurkschat on the occasion of his retirement.