title: Synthesis, characterization, and lactide polymerization activity of group 4 metal complexes containing two bis(phenolate) ligands.
abstract: A series of group 4 metal complexes Zr-(1)(2), Zr-(2)(2), Zr-(3)(2), Zr-(4)(2), Zr-(5)(2), Hf-(1)(2), and Hf-(4)(2) containing two bridged bis(phenolate) ligands of the (OSSO)-type were prepared by the reaction of the corresponding bis(phenol) and group 4 metal precursor MX(4) (X = O(i)Pr, CH(2)Ph) and isolated as robust, colorless crystals. NMR spectra indicate D(2) symmetry, in agreement with the solid state structure determined by single crystal X-ray diffraction study of the complexes Zr-(1)(2), Hf-(1)(2), Zr-(3)(2), Zr-(4)(2), and Zr-(5)(2). The complexes with the 1,4-dithiabutanediyl bridged ligands exhibit a highly symmetric coordination around the metal center. The introduction of the rigid trans-1,2-cyclohexanediyl bridged ligands led to a distorted coordination around the metal center in Zr-(4)(2) and Zr-(5)(2) when the ortho substituent is tert-butyl and the para substituent is larger than methyl. The complexes Zr-(1)(2), Zr-(2)(2), Zr-(3)(2), Zr-(4)(2) as well as Hf-(1)(2) and Hf-(4)(2) initiated the ring-opening polymerization of meso-lactide at 100 °C to give heterotactic polylactide with pronounced heterotacticity (>70%) and varying polydispersity (1.05 < M(w)/M(n) < 1.61). As shown by kinetic studies, zirconium complex Zr-(1)(2) polymerized meso-lactide faster than the homologous hafnium complex Hf-(1)(2).
authors.affiliation: Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, D-52056 Aachen, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Sauer
authors.forename: Jean-Charles
authors.initials: JC
authors.lastname: Buffet
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Spaniol
authors.forename: Haruki
authors.initials: H
authors.lastname: Nagae
authors.forename: Kazushi
authors.initials: K
authors.lastname: Mashima
authors.forename: Jun
authors.initials: J
authors.lastname: Okuda
mesh_terms: D056831:Coordination Complexes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004146:Dioxanes / Q000737:chemistry*; D006195:Hafnium / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D010636:Phenols / Q000737:chemistry*; D011091:Polyesters / Q000138:chemical synthesis*; D058105:Polymerization; D015040:Zirconium / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D004146:Dioxanes; D008024:Ligands; D010636:Phenols; D011091:Polyesters; C033616:poly(lactide); C091880:dilactide; D015040:Zirconium; D006195:Hafnium