Preparation and structures of enantiomeric dinuclear zirconium and hafnium complexes containing two homochiral N atoms, and their catalytic property for polymerization of rac-lactide

Abstract

The hydroxy- and phenoxy-bridged dinuclear zirconium and hafnium complexes and of an amine-pyridine-bis(phenolate) ligand (H(2)L) were prepared from the reaction of Na(2)L and ZrCl(4) in the presence of 0.5 equiv of water in THF, while the reaction of H(2)L with NaH and then with ZrCl(4) in the freshly distilled THF gave an eight-coordinate bis(homoleptic) mononuclear complex L(2)Zr (). Two homochiral N atoms were created in each complex upon coordination of the unsymmetric tertiary amine ligands to the metal centers. Enantiomeric dinuclear complexes and both undergo spontaneous resolution during crystallization. The molecular structure of each enantiomer of and , as well as the structure of , was determined by X-ray analysis and the circular dichroism spectra of N(R)N(R)- and N(S)N(S)- were studied. The racemates of and catalyzed controlled polymerization of rac-lactide in terms of the linearity of molecular weight versus conversion, forming isotactic-rich polylactide in high yields with a narrow polydispersity.