title: Lactide polymerization catalyzed by Mg and Zn diketiminate complexes with flexible ligand frameworks.
abstract: Diketimine ligands bearing N-benzyl, N-9-anthrylmethyl and N-mesitylmethyl substituents (nacnac(Bn)H, nacnac(An)H, and nacnac(Mes)H) were prepared from condensation of the amine with either acetyl acetone or its ethylene glycol monoketal. Chlorination with N-chlorosuccinimide in the 3-position yielded Clnacnac(Bn)H and Clnacnac(An)H. The ligands were reacted with Zn(TMSA)2 (TMSA = N(SiMe3)2) to yield nacnac(An)Zn(TMSA) and Clnacnac(Bn)Zn(TMSA). Protonation with isopropanol afforded nacnac(An)ZnOiPr and Clnacnac(Bn)ZnOiPr. Reaction of the diketimines with Mg(TMSA)2 afforded nacnac(An)Mg(TMSA), nacnac(Mes)Mg(TMSA), Clnacnac(Bn)Mg(TMSA) and Clnacnac(An)Mg(TMSA). Subsequent protonation with tert-butanol produced nacnac(Mes)MgOtBu and Clnacnac(Bn)MgOtBu, but only decomposition was observed with N-anthrylmethyl substituents. Most complexes were characterized by X-ray diffraction studies. TMSA complexes were monomeric and alkoxide complexes dimeric in the solid state. All alkoxide complexes, as well as nacnac(An)Mg(TMSA)/BnOH and Clnacnac(An)Mg(TMSA)/BnOH were moderately to highly active in rac-lactide polymerization (90% conversion in 30 s to 3 h). nacnac(An)ZnOiPr produced highly heterotactic polymers (P(r) = 0.90), Clnacnac(Bn)MgOtBu/BnOH produced slightly isotactic polymers at -30 °C (P(r) = 0.43), and all other catalysts produced atactic polymers with a slight heterotactic bias.
authors.affiliation: Centre in Green Chemistry and Catalysis (CGCC), Département de chimie, Université de Montréal, 2900 Boul. E.-Montpetit, Montréal, QC, H3T 1J4, Canada. Frank.Schaper@umontreal.ca.
authors.forename: Todd J J
authors.initials: TJ
authors.lastname: Whitehorne
authors.forename: Boris
authors.initials: B
authors.lastname: Vabre
authors.forename: Frank
authors.initials: F
authors.lastname: Schaper
mesh_terms: D002384:Catalysis; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004146:Dioxanes / Q000737:chemistry*; D008024:Ligands; D008274:Magnesium / Q000737:chemistry*; D008968:Molecular Conformation; D058105:Polymerization; D015032:Zinc / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D004146:Dioxanes; D008024:Ligands; C091880:dilactide; D008274:Magnesium; D015032:Zinc