Magnesium complexes based on an amido-bis(pyrazolyl) ligand: Synthesis, crystal structures, and use in lactide polymerization

The coordination chemistry of the tridentate N,N,N pro-ligand bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl]amine (1, LH) with dialkylmagnesium and monoalkyl magnesium halides has been studied. Reaction of 2 equiv of 1 with Mg(nBu)2 gave bis(amido) complex [L]2Mg (3), which is monomeric in the solid state. Alkane elimination reactions from iPrMgCl and MeMgI with 1 equiv of 1 afforded the corresponding halide complexes {[L]MgCl}2 (4) and {[L]MgI}2 (5), which both feature dimeric structures in the solid state, with a chelating and spanned coordination mode of the tridentate ligand, respectively. Additionally, bis(amido) complex 3 was shown to be active for the ring-opening polymerization of racemic lactide at room temperature to yield atactic polylactides with high initiation efficiencies and relatively narrow polydispersities (Mw/Mn = 1.28–1.34).

Monomeric diamido bis(ligand) and dimeric amido-halide magnesium complexes based on a tridentate NNN ligand are respectively shown to be active in lactide polymerization and to feature a different coordination mode of the NNN ligand according to the nature of the halide ion.Figure optionsDownload as PowerPoint slide