title: Mechanistic Insight into the Stereochemical Control of Lactide Polymerization by Salan-Aluminum Catalysts.
abstract: Alkyl aluminum complexes of chiral salan ligands assembled around the 2,2'-bipyrrolidine core form as single diastereomers that have identical configurations of the N donors. Active catalysts for the polymerization of lactide were formed upon the addition of benzyl alcohol. Polymeryl exchange between enantiomorphous aluminum species had a dramatic effect on the tacticity of the poly(lactic acid) (PLA) in the polymerization of racemic lactide (rac-LA): The enantiomerically pure catalyst of the nonsubstituted salan ligand led to isotactic PLA, and the racemic catalyst exhibited lower stereocontrol. The enantiomerically pure catalyst of the chloro-substituted salan ligand led to PLA with a slight tendency toward heterotacticity, whereas the racemic catalyst led to PLA of almost perfect heterotacticity following an insertion/auto-inhibition/exchange mechanism.
authors.affiliation: School of Chemistry, Tel Aviv University, Ramat Aviv, Tel Aviv 69978 (Israel).
authors.forename: Konstantin
authors.initials: K
authors.lastname: Press
authors.affiliation: School of Chemistry, Tel Aviv University, Ramat Aviv, Tel Aviv 69978 (Israel).
authors.forename: Israel
authors.initials: I
authors.lastname: Goldberg
authors.affiliation: School of Chemistry, Tel Aviv University, Ramat Aviv, Tel Aviv 69978 (Israel). moshekol@post.tau.ac.il.
authors.forename: Moshe
authors.initials: M
authors.lastname: Kol
keywords: aluminum complexes; chiral salan ligands; poly(lactic acid); polymerization; stereoselective catalysis