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

Abstract

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 dif-[a] Synthesis and Characterization The reaction of ketoimine LH [L = MeNacac = MeNC(Me)-CHC(Me)O] with an equimolar amount of diethylzinc in THF at -60°C occurred with elimination of ethane and formation of Scheme 1. Synthesis of 1-5.

Zn(HMDS)2 as a Versatile Transesterification Catalyst for Polyesters Synthesis and Degradation toward a Circular Materials Economy Approach

“…Our group is committed to seeking such a multifunctional catalyst. Metal zinc represents one of the most attractive candidates due to its inexpensive, nontoxic, and biocompatible advantages. − Most of the reported zinc catalysts in ROP require the participation of delicate and complicated supporting ligands, such as β-diiminate Zn complex synthesized by Coates, to improve the reactivity and controllability, by changing the steric resistance and electrical properties of the central metal. − The synthesis of ligands increases the cost of catalysts and therefore reduces their practice industry application value. Herein, we report a catalyst based on a simple, supporting ligand-free zinc bis­[bis­(trimethylsilyl)­amide].…”

Heterolepic β‐Ketoiminate Zinc Phenoxide Complexes as Efficient Catalysts for the Ring Opening Polymerization of Lactide

“…They also found that the metal substituents as well as the electron‐donating substituents of the pyrrolidine‐ β ‐ketoiminate ligands play an important role in the activity and stereoselectivity of the polymerization process. Recently, we reported the ROP of LA by using homoleptic (L 2 Zn) and heteroleptic (LZnOAr) β ‐ketoiminate zinc complexes and demonstrated that the heteroleptic complexes LZnOAr containing a supplementary phenoxide or Lewis base coordinated to the Zn atom are highly active catalysts . In addition, a large number of β ‐ketoiminate metal complexes were reported, which showed excellent reactivity to the ROP of cyclic esters under milder reaction condition in a controlled mechanism…”

Fluorinated β‐Ketoiminate Zinc Complexes: Synthesis, Structure and Catalytic Activity in Ring Opening Polymerization of Lactide

“…These findings demonstrate that the reaction rates of the alcoholysis reaction of 1 and 2 with BnOH are comparable. Comparing the catalytic activity of fluorinated β ‐ketoiminate zinc complex 2 in the ROP of lactide with that of non‐fluorinated β ‐ketoiminate zinc analogues [5a] clearly shows, that the introduction of electron‐withdrawing CF 3 and C 6 F 5 groups to the β ‐ketoiminate ligand backbone reduces the catalytic activity.…”