Zirconium and hafnium complexes bearing pyrrolidine derived salalen-type {ONNO} ligands and their application for ring-opening polymerization of lactidesElectronic supplementary information (ESI) available. CCDC 1539661-1539664. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7dt02113e

The reactions of pyrrolidine derived salalen-type {ONNO} ligands ( S )-L 1-3 -H 2 with 1 equiv. M(O i Pr) 4 (HO i Pr) (M = Zr or Hf) in diethyl ether yielded complexes [L 1-3 M(O i Pr) 2 ] (L = L 1 , M = Zr ( 1 ); L = L 2 , M = Zr ( 2 ), Hf ( 3 ); L = L 3 , M = Zr ( 4 ), Hf ( 5 )). All of these complexes were well characterized by NMR spectroscopy, elemental analyses and single-crystal X-ray analysis in the case of complexes 1 and 3-5 . X-ray structural determination revealed that these complexes were analogous mononuclear species and had a similar structure in which the metal centers were six-coordinated to two oxygen atoms and two nitrogen atoms of one ligand and two oxygen atoms of two isopropoxy groups. All of these complexes efficiently initialized the ring-opening polymerization of lactides to afford polymers with controlled molecular weight and narrow polydispersity. Furthermore, the ring-opening polymerization of rac -lactide catalyzed by complexes 1-5 afforded isotactic-enriched polymers in solution ( P m = 0.74-0.80) and under melt conditions ( P m = 0.63-0.72). Zirconium and hafnium complexes [(( S )-L)M(O i Pr) 2 ] bearing salalen-type {ONNO} ligands have been synthesized and applied as efficient isoselective catalysts for ring-opening polymerization of rac -lactide.