Phosphasalen group IV metal complexes: synthesis, characterization and ring opening polymerization of lactide

proceeded diastereoselectively giving rise to Ti complexes 7a-c in octahedral geometry with cis-β wrapping of the ligand. The complexes have been tested for the ROP of rac-lactide. The neutral phosphasalen Ti and Zr complexes showed only poor activity probably due to the encumbered and electron donating nature of the phosphasalen ligand. In contrast, the cationic Zr alkoxides 5a, 6a and 6b are effective initiators for the controlled and hetero-selective ROP of rac-lactide.