Dinuclear group 4 alkoxides: Excellent initiators for ring-opening polymerization of cyclic esters

Abstract Three new dinuclear group 4 metal alkoxides [Ti 2 ( μ -O i Pr)(O i Pr) 4 L] ( 1 ), [Zr 2 ( μ -O i Pr)(O i Pr) 4 L] ( 2 ) and [Hf 2 ( μ -O i Pr)(O i Pr) 4 L] ( 3 ) have been prepared in good yields from the reaction of N, N-di(salicylidene)-2-hydroxyphenylmethanediamine (L-H 3 ) and two equiv. [M(O i Pr) 4 (HO i Pr) n ], respectively. Complexes 1 – 3 have been characterized by 1 H NMR, 13 C NMR, elemental analyses and X-ray diffraction analyses. The molecular structures of complexes 1 and 3 reveal dinuclear species in which the metal centers are hexa-coordinated to one oxygen atom and one nitrogen atom of the ligand, to two oxygen atoms of two isopropoxy groups, and to two bridging oxygen atoms of one phenolate group of ligand and one isopropoxy group. Complexes 1 – 3 are excellent catalysts/initiators for ring-opening polymerization of e -caprolactone and L- and rac -lactide to give the corresponding polyesters.