Synthesis of ChiralC2-Symmetric Bimetallic Zinc Complexes of Amido-Oxazolinates and Their Application in Copolymerization of CO2and Cyclohexene Oxide

Abstract

A family of new chiral C2 symmetric amido-oxazolinate ligands H2L (1 a-1 d) that are bridged by three different linkers based on m-phenylenediamine, 4-(4’-aminobenzyl)benzenamine, and 1,8-diaminoanthracene have been synthesized in high yields (85-90 %). Treatment of ligands (1 a-1 d) with two equiv. of Zn[N(SiMe3)2]2 in dry toluene generated a series of heteroleptic dizinc complexes (L)[ZnN(SiMe3)2]2 (2 a-2 d) and reaction of 1 b with one equiv. of Zn[N(SiMe3)2]2 leads to formation of a homoleptic binuclear zinc complex (L)2Zn2 (3 b) in good yield. Complexes 2 a-2 d were found to be effective catalysts for asymmetric alternating copolymerization of CO2 and cyclohexene oxide (CHO). The catalyst 2 a is more active towards polycarbonate formation (78 % carbonate linkages), while the catalyst 2 d generates highly isotactic poly(cyclohexene carbonate) (86 % of m-centered tetrads).