Mononuclear and dinuclear tetravalent zirconium compounds as catalysts for the synthesis of aliphatic polyesters and aliphatic polycarbonates

Abstract

Two categories of tetravalent Zr(IV) compounds were synthesized using Schiff base proligands (L1H−L5H) and appropriate Zr(IV) alkoxide reagents. The isopropoxide Zr(IV) compounds (1–5) were dimeric, where the two Zr(IV) centers were connected through the isopropoxide group, and the geometry around the Zr(IV) center was distorted octahedral. The tert-butoxide Zr(IV) compounds (6–8) were monomeric, with the Zr(IV) center having a coordination number of five. The dimeric complexes showed catalytic activity towards the ring-opening polymerization (ROP) of rac-LA and negligible activity for ring-opening copolymerization (ROCOP) of cyclohexene oxide with CO₂. The monomeric complexes produced polyesters (through ROP and ROCOP) and aliphatic polycarbonates through ROCOP reactions. The mononuclear compounds resulted in >99 % carbonate linkage in the polycarbonate chain.