Journal
JOURNAL OF ORGANOMETALLIC CHEMISTRY
Volume 690, Issue 24-25, Pages 5881-5891Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.jorganchem.2005.07.070
Keywords
zinc; N-heterocyclic carbenes; polymerization catalysis; lactide; polylactide
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A series of zinc complexes of monodentate N-heterocyclic carbenes (NHCs) and a new sterically bulky bidentate pyridyl-NHC ligand have been synthesized and characterized by spectroscopic and X-ray crystallographic methods. Dinuclear alkoxide complexes of monodentate NHC complexes with 2,4,6-trimethylphenyl substituents appear to form monomeric species in solution and show good control and activity for lactide polymerization, including mild stereoelectivity as indicated by formation of heterotactic-enriched polylactide in D,L-lactide polymerizations. Kinetics studies revealed an overall second order rate law, first order in [LA] and [catalyst]. Efforts to obtain Zn-alkoxide complexes of a more sterically hindered NHC with 2,6-diisopropylphenyl groups were unsuccessful due to Zn-NHC bond scission. Ligand dissociation was also observed in attempts to prepare Zn-alkoxide complexes of the bidentate pyridyl-NHC system, despite its chelating nature. (c) 2005 Elsevier B.V. All rights reserved.
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