Chiral β-diketiminate-supported magnesium alkyl complexes: Synthesis and their application in the polymerization of rac-lactide

A series of novel magnesium alkyl complexes bearing chiral beta-diketiminate ligands [CH3C[NCH(CH3)Ph] CHC(NAr)CH3]Mg(Bu-n)(THF) (Ar = 2,6-(Pr2C6H3)-Pr-i (1)), [CH3C[NCH(CH3)Naph] CHC(NAr)CH3]Mg(Bu-n) (THF) (Naph = 1-naphthyl; Ar = 2,6-(Pr2C6H3)-Pr-i (2), 2,6-Et2C6H3 (3), 2,6-Me2C6H3 (4)) and [CH{C[NCH(CH3)Naph]CH3}(2)]Mg(Bu-n)(THF) (5) have been prepared by reaction of the corresponding chiral ligand precursors (HL1-HL5) with (MgBu2)-Bu-n. These complexes were characterized by various spectroscopic methods, and the solidstate structures of compounds 1, 3 and 4 were further confirmed by single-crystal X-ray diffraction analyses. Complexes 1-5 are active catalysts for the ring-opening polymerization (ROP) of rac-lactide, leading to heterotactic-rich polylactides within 5 min under mild conditions. These complexes show medium to high heteroselectivity (P-r = 0.71-0.92).