Magnesium and Zinc Complexes Supported by N,N,O Tridentate Ligands: Synthesis and Catalysis in the Ring-Opening Polymerization of rac-Lactide and alpha-Methyltrimethylene Carbonate

摘要

A series of racemic biphenyl-or binaphthyl-based aminophenols were treated with 1 equiv. of Mg[N(SiMe3)(2)](2) or Zn[N(SiMe3)(2)](2) to provide eight heteroleptic magnesium and zinc silylamido complexes (Mg, 1a-5a; Zn, 1b, 3b, 5b). Single-crystal X-ray diffraction studies on typical magnesium complex 5a and zinc complexes 1b, 3b, and 5b showed a tridentate chelating mode of the ligand and a distorted tetrahedral geometry around the metal center. All of these complexes proved to be efficient initiators for the ring-opening polymerization of rac-lactide in toluene and THF. Microstructure analysis of the resultant poly(rac-lactide) samples by homonuclear-decoupled H-1 NMR spectroscopy revealed heterotacticities ranging from 0.45 to 0.69. These complexes were also applied as initiators in the polymerization of racemic alpha a-methyltrimethylene carbonate in toluene and exhibited moderate to high regioselectivities; the most regioregular polymer was obtained with magnesium complex 4a (X-reg = 0.93).