A pinch of silver salt to enable rac-lactide ring-opening polymerisation at room temperature using Ti-salen complexes†

Abstract

Exploiting non-covalent interactions (NCIs) has become a powerful tool in catalyst design, including those for polymerisation reactions. Herein we report a simple strategy relying on the addition of silver salt to Ti-salen complexes, leading to Ti/Ag cooperativity via cation-π interactions. Three different Ti-salen complexes were investigated alongside several silver salts. In all cases, these Ti/Ag systems led to good or high activity at room temperature for rac-lactide ROP, a rare feature for Ti-based catalysts. Interestingly, the weakly coordinating anion (WCA) of the silver salt was found not only to affect activity but also stereocontrol in the polymerisation. Heterotactic PLA with P_r up to 0.7 was obtained.