Zirconium vs Aluminum Salalen Initiators for the Production of Biopolymers

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, 1H(2), monometallic complexes were observed in solution and solid state. Complex Zr(1)((OPr)-Pr-i)(2) was able to produce isotactic polylactide (PLA) from rac-lactide (P-m up to 0.85) in solution at 50 degrees C; in the melt (130 degrees 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 approximate to 0.6). Zr(1)((OPr)-Pr-i)(2) was also able to produce copolymers with lactide and e-caprolactone, producing copolymers of a blocky nature.