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

Abstract

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 1H NMR spectroscopy revealed heterotacticities ranging from 0.45 to 0.69. These complexes were also applied as initiators in the polymerization of racemic α‐methyltrimethylene carbonate in toluene and exhibited moderate to high regioselectivities; the most regioregular polymer was obtained with magnesium complex 4a (Xreg = 0.93).