Synthesis of Chiral C2-Symmetric Bimetallic Zinc Complexes of Amido-Oxazolinates and Their Application in Copolymerization of CO2 and Cyclohexene Oxide

A family of new chiral C-2 symmetric amido-oxazolinate ligands H2L (1a-1d) 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 (1a-1d) with two equiv. of Zn[N(SiMe3) (2)](2) in dry toluene generated a series of heteroleptic dizinc complexes (L)[ZnN(SiMe3)(2)](2) (2a-2d) and reaction of 1b with one equiv. of Zn[ N(SiMe3)(2)](2) leads to formation of a homo-leptic binuclear zinc complex (L)(2)Zn-2 (3b) in good yield. Complexes 2a-2d were found to be effective catalysts for asymmetric alternating copolymerization of CO2 and cyclohexene oxide (CHO). The catalyst 2a is more active towards polycarbonate formation (78% carbonate linkages), while the catalyst 2d generates highly isotactic poly(cyclohexene carbonate) (86% of m-centered tetrads).