Copolymerization of Cyclohexene Oxide with CO2 by Using Intramolecular Dinuclear Zinc Catalysts
- 30 May 2005
- journal article
- Published by Wiley in Chemistry – A European Journal
- Vol. 11 (12) , 3668-3678
- https://doi.org/10.1002/chem.200401159
Abstract
The intramolecular dinuclear zinc complexes generated in situ from the reaction of multidentate semi-azacrown ether ligands with Et(2)Zn, followed by treatment with an alcohol additive, were found to promote the copolymerization of CO(2) and cyclohexene oxide (CHO) with completely alternating polycarbonate selectivity and high efficiency. With this type of novel initiator, the copolymerization could be accomplished under mild conditions at 1 atm pressure of CO(2), which represents a significant advantage over most catalytic systems developed for this reaction so far. The copolymerization reaction was demonstrated to be a living process as a result of the narrow polydispersities and the linear increase in the molecular weight with conversion of CHO. In addition, the solid-state structure of the dinuclear zinc complex was characterized by X-ray crystal structural analysis and can be considered as a model of the active catalyst. On the basis of the various efforts made to understand the mechanisms of the catalytic reaction, including MALDI-TOF mass analysis of the copolymers' end-groups, the effect of alcohol additives on the catalysis and CO(2) pressure on the conversion of CHO, as well as the kinetic data gained from in situ IR spectroscopy, a plausible catalytic cycle for the present reaction system is outlined. The copolymerization is initiated by the insertion of CO(2) into the Zn--OEt bond to afford a carbonate-ester-bridged complex. The dinuclear zinc structure of the catalyst remains intact throughout the copolymerization. The bridged zinc centers may have a synergistic effect on the copolymerization reaction; one zinc center could activate the epoxide through its coordination and the second zinc atom may be responsible for carbonate propagation by nucleophilic attack by the carbonate ester on the back side of the cis-epoxide ring to afford the carbonate. The mechanistic implication of this is particularly important for future research into the design of efficient and practical catalysts for the copolymerization of epoxides with CO(2.).Keywords
This publication has 75 references indexed in Scilit:
- Highly Active, Binary Catalyst Systems for the Alternating Copolymerization of CO2 and Epoxides under Mild ConditionsAngewandte Chemie, 2004
- The Ethylsulfinate Ligand: A Highly Efficient Initiating Group for the Zinc β-Diiminate Catalyzed Copolymerization Reaction of CO2 and EpoxidesOrganometallics, 2002
- A Dinuclear Zn Catalyst for the Asymmetric Nitroaldol (Henry) ReactionAngewandte Chemie, 2002
- Bis 2,6-difluorophenoxide Dimeric Complexes of Zinc and Cadmium and Their Phosphine Adducts: Lessons Learned Relative to Carbon Dioxide/Cyclohexene Oxide Alternating Copolymerization Processes Catalyzed by Zinc PhenoxidesJournal of the American Chemical Society, 2000
- Isolation of a Pyridinium Alkoxy Ion Bridged Dimeric Zinc Complex for the Coupling Reactions of CO2 and EpoxidesPublished by Wiley ,2000
- Optically Active Polycarbonates: Asymmetric Alternating Copolymerization of Cyclohexene Oxide and Carbon DioxideJournal of the American Chemical Society, 1999
- Homopolymerization and Copolymerization of Cyclohexene Oxide with Carbon Dioxide Using Zinc and Aluminum CatalystsMacromolecules, 1999
- Mechanistic Aspects of the Copolymerization of CO2 and Epoxides by Soluble Zinc Bis(phenoxide) Catalysts as Revealed by Their Cadmium AnaloguesJournal of the American Chemical Society, 1998
- Biodegradability of CO2 Copolymers Synthesized by Using Macromolecule—Bimetal CatalystsPolymers for Advanced Technologies, 1996
- 4,7,10,23-Tetramethyl-17-oxa-1,4,7,10,13,23-hexaazabicyclo[11.7.5]pentacosane (L), a Two-Binding-Site Ligand for the Assembly of the [Zn2(.mu.-OH)2]2+ ClusterInorganic Chemistry, 1995