Go to  Advanced Search

An unusually stable chiral ethyl zinc complex : reactivity and polymerization of lactide

Show full item record

Files in this item

Files Size Format Description   View
ubc_2008_fall_labourdette_guillaume.pdf 1.678Mb Adobe Portable Document Format   View/Open
Title: An unusually stable chiral ethyl zinc complex : reactivity and polymerization of lactide
Author: Labourdette, Guillaume
Degree: Master of Science - MSc
Program: Chemistry
Copyright Date: 2008
Subject Keywords Lactide;Chiral;Polymerization;Zinc;Biodegradable;Catalyst
Issue Date: 2008-09-18
Publisher University of British Columbia
Abstract: The racemic (±)-2,4-di-tert-butyl-6-(((2-(dimethylamino)cyclohexyl)(methyl) amino)methyl)phenol ((±)-(NNMeOtBu)H), (±)-2,4-di-tert-butyl-6-((2-(dimethylamino) cyclohexylamino)methyl)phenol ((±)-(NNHOtBu)H), and (±)-2-(((2-(dimethylamino) cyclohexyl)(methyl)amino) methyl)phenol ((±)-(NNMeOH)H) are chiral ancillary NNO proligands, which synthesis was adapted from a published procedure. Reaction of (±)-(NNMeOtBu)H ((±)-2), (±)-(NNMeOH)H ((±)-3) and (±)-(NNHOtBu)H ((±)-1) with ZnEt2 successfully yielded the corresponding zinc ethyl complexes (±)-5, (±)-6 and (±)-7 respectively; the enantiomerically pure (R,R)-5 was synthesized from (R,R)-2. NMR spectroscopy experiments and X-ray crystallography allowed identification of two stereoisomers for (±)-5, which were observed in solution and in the solid state. The two stereoisomers, 5-α and 5-β, are in equilibrium in solution, with 5-β being thermodynamically favored. The zinc ethyl complexes were found to be unreactive towards weakly acidic alcohols (methanol, ethanol, isopropanol). However, the zinc chloride complex (±)-(NNMeOtBu)ZnCl ((±)-8) and the zinc phenoxide (NNMeOtBu)ZnOPh ((±)-9 and (R,R)-9) could be isolated and characterized. Comparison of the reactivity of both (±)-5 and the reported L₁ZnEt (L₁ = 2,4-di-tert-butyl-6- {[(2'-dimethylaminoethyl) methylamino]methyl}phenolate) in presence of pyridine led to the proposal of a dissociative mechanism explaining the fundamental difference between the two zinc ethyl species. Polymerization of rac-lactide catalyzed by 9 showed that the complex, in its racemic or enantiomerically pure version, has a slow activity and is not stereoselective.
Affiliation: Science, Faculty of
URI: http://hdl.handle.net/2429/2266
Scholarly Level: Graduate

This item appears in the following Collection(s)

Show full item record

UBC Library
1961 East Mall
Vancouver, B.C.
Canada V6T 1Z1
Tel: 604-822-6375
Fax: 604-822-3893