Alkaline earth metal complexes of a chiral polyether as initiator for the ring-opening polymerization of lactide

Abstract

A chiral, tetradentate polyether ligand with a trans-1,2-cyclohexanediyl backbone, bis(methoxyethoxy)-trans-1,2-cyclohexane (5), was synthesized as both a racemate and the (S,S) enantiomer. 5 was found to form stable adducts with alkaline earth metal amides [M{N(SiMe₃)₂}₂(thf)_x] (M = Mg (x = 0), Ca (x = 2) and Sr (x = 2/3)), [Ca{N(SiHMe₂)₂}₂(thf)] as well as with hydrocarbyl compounds [Mg(CH₂SiMe₃)₂] and [Ca(η³-C₃H₅)₂]. X-ray diffraction study of the bis(amide) [((S,S)-5)Ca{N(SiMe₃)₂}₂] and of the bis(allyl) [(rac-5)Ca(η³-C₃H₅)₂] was performed. The complexes obtained were tested as initiators for the ring-opening polymerization of meso-, racemic and L-lactide.