Zirconium vs Aluminum Salalen Initiators for the Production of Biopolymers

Abstract

Herein we report the synthesis and full characterization (NMR and solid-state structures) for a series of Zr(IV), Hf(IV), and Al(III) salalen complexes, together with salen bimetallic counterparts. With the salalen ligand, 1 H 2, monometallic complexes were observed in solution and solid state. Complex Zr( 1 )(O i Pr) 2 was able to produce isotactic polylactide (PLA) from rac -lactide ( P m up to 0.85) in solution at 50 °C; in the melt (130 °C) this reduced to ca. 0.75. Al( 1 )Me was significantly less active and produced PLA with only a very modest isotactic enchainment ( P m ≈ 0.6). Zr( 1 )(O i Pr) 2 was also able to produce copolymers with lactide and ε-caprolactone, producing copolymers of a “blocky” nature.