Enantioselective polymerization of epoxides using biaryl-linked bimetallic cobalt catalysts: A mechanistic study

Handle URI:
http://hdl.handle.net/10754/563152
Title:
Enantioselective polymerization of epoxides using biaryl-linked bimetallic cobalt catalysts: A mechanistic study
Authors:
Ahmed, Syud M.; Poater, Albert; Childers, M. Ian; Widger, Peter C B; Lapointe, Anne M.; Lobkovsky, Emil B.; Coates, Geoffrey W.; Cavallo, Luigi ( 0000-0002-1398-338X )
Abstract:
The enantioselective polymerization of propylene oxide (PO) using biaryl-linked bimetallic salen Co catalysts was investigated experimentally and theoretically. Five key aspects of this catalytic system were examined: (1) the structural features of the catalyst, (2) the regio- and stereoselectivity of the chain-growth step, (3) the probable oxidation and electronic state of Co during the polymerization, (4) the role of the cocatalyst, and (5) the mechanism of monomer enchainment. Several important insights were revealed. First, density functional theory (DFT) calculations provided detailed structural information regarding the regio- and stereoselective chain-growth step. Specifically, the absolute stereochemistry of the binaphthol linker determines the enantiomer preference in the polymerization, and the interaction between the salen ligand and the growing polymer chain is a fundamental aspect of enantioselectivity. Second, a new bimetallic catalyst with a conformationally flexible biphenol linker was synthesized and found to enantioselectively polymerize PO, though with lower enantioselectivity than the binaphthol linked catalysts. Third, DFT calculations revealed that the active form of the catalyst has two active exo anionic ligands (chloride or carboxylate) and an endo polymer alkoxide which can ring-open an adjacent cobalt-coordinated epoxide. Fourth, calculations showed that initiation is favored by an endo chloride ligand, while propagation is favored by the presence of two exo carboxylate ligands. © 2013 American Chemical Society.
KAUST Department:
Biological and Environmental Sciences and Engineering (BESE) Division; KAUST Catalysis Center (KCC); Physical Sciences and Engineering (PSE) Division; Chemical Science Program
Publisher:
American Chemical Society (ACS)
Journal:
Journal of the American Chemical Society
Issue Date:
18-Dec-2013
DOI:
10.1021/ja409521z
Type:
Article
ISSN:
00027863
Sponsors:
We thank the NSF (CHE-1136607 and CHE-1112278) and the King Abdullah University of Science and Technology (KAUST; Award KUS-C1-018-02) for financial support. We also thank Dr. Ivan Keresztes and Mr. Anthony Condo for assistance with NMR experiments to confirm the structure of 8. A.P. thanks the Spanish MINECO for a Ramon y Cajal contract (RYG-2009-5226), European Commission for a Career Integration Grant (CIG09-GA-2011-293900), and Generalitat de Catalunya (2012BE100824).
Is Supplemented By:
Ahmed, S. M., Poater, A., Childers, M. I., Widger, P. C. B., LaPointe, A. M., Lobkovsky, E. B., … Cavallo, L. (2014). CCDC 1001988: Experimental Crystal Structure Determination [Data set]. Cambridge Crystallographic Data Centre. https://doi.org/10.5517/cc12mn6k; DOI:10.5517/cc12mn6k; HANDLE:http://hdl.handle.net/10754/624318; Ahmed, S. M., Poater, A., Childers, M. I., Widger, P. C. B., LaPointe, A. M., Lobkovsky, E. B., … Cavallo, L. (2014). CCDC 1001989: Experimental Crystal Structure Determination [Data set]. Cambridge Crystallographic Data Centre. https://doi.org/10.5517/cc12mn7l; DOI:10.5517/cc12mn7l; HANDLE:http://hdl.handle.net/10754/624319
Appears in Collections:
Articles; Physical Sciences and Engineering (PSE) Division; Chemical Science Program; KAUST Catalysis Center (KCC); Biological and Environmental Sciences and Engineering (BESE) Division

Full metadata record

DC FieldValue Language
dc.contributor.authorAhmed, Syud M.en
dc.contributor.authorPoater, Alberten
dc.contributor.authorChilders, M. Ianen
dc.contributor.authorWidger, Peter C Ben
dc.contributor.authorLapointe, Anne M.en
dc.contributor.authorLobkovsky, Emil B.en
dc.contributor.authorCoates, Geoffrey W.en
dc.contributor.authorCavallo, Luigien
dc.date.accessioned2015-08-03T11:36:59Zen
dc.date.available2015-08-03T11:36:59Zen
dc.date.issued2013-12-18en
dc.identifier.issn00027863en
dc.identifier.doi10.1021/ja409521zen
dc.identifier.urihttp://hdl.handle.net/10754/563152en
dc.description.abstractThe enantioselective polymerization of propylene oxide (PO) using biaryl-linked bimetallic salen Co catalysts was investigated experimentally and theoretically. Five key aspects of this catalytic system were examined: (1) the structural features of the catalyst, (2) the regio- and stereoselectivity of the chain-growth step, (3) the probable oxidation and electronic state of Co during the polymerization, (4) the role of the cocatalyst, and (5) the mechanism of monomer enchainment. Several important insights were revealed. First, density functional theory (DFT) calculations provided detailed structural information regarding the regio- and stereoselective chain-growth step. Specifically, the absolute stereochemistry of the binaphthol linker determines the enantiomer preference in the polymerization, and the interaction between the salen ligand and the growing polymer chain is a fundamental aspect of enantioselectivity. Second, a new bimetallic catalyst with a conformationally flexible biphenol linker was synthesized and found to enantioselectively polymerize PO, though with lower enantioselectivity than the binaphthol linked catalysts. Third, DFT calculations revealed that the active form of the catalyst has two active exo anionic ligands (chloride or carboxylate) and an endo polymer alkoxide which can ring-open an adjacent cobalt-coordinated epoxide. Fourth, calculations showed that initiation is favored by an endo chloride ligand, while propagation is favored by the presence of two exo carboxylate ligands. © 2013 American Chemical Society.en
dc.description.sponsorshipWe thank the NSF (CHE-1136607 and CHE-1112278) and the King Abdullah University of Science and Technology (KAUST; Award KUS-C1-018-02) for financial support. We also thank Dr. Ivan Keresztes and Mr. Anthony Condo for assistance with NMR experiments to confirm the structure of 8. A.P. thanks the Spanish MINECO for a Ramon y Cajal contract (RYG-2009-5226), European Commission for a Career Integration Grant (CIG09-GA-2011-293900), and Generalitat de Catalunya (2012BE100824).en
dc.publisherAmerican Chemical Society (ACS)en
dc.titleEnantioselective polymerization of epoxides using biaryl-linked bimetallic cobalt catalysts: A mechanistic studyen
dc.typeArticleen
dc.contributor.departmentBiological and Environmental Sciences and Engineering (BESE) Divisionen
dc.contributor.departmentKAUST Catalysis Center (KCC)en
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
dc.contributor.departmentChemical Science Programen
dc.identifier.journalJournal of the American Chemical Societyen
dc.contributor.institutionDepartment of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, NY 14853-1301, United Statesen
dc.contributor.institutionDepartment de Química, Universitat de Girona, Campus de Motilivi, E-17071 Girona, Spainen
kaust.authorCavallo, Luigien
kaust.authorPoater, Alberten
dc.relation.isSupplementedByAhmed, S. M., Poater, A., Childers, M. I., Widger, P. C. B., LaPointe, A. M., Lobkovsky, E. B., … Cavallo, L. (2014). CCDC 1001988: Experimental Crystal Structure Determination [Data set]. Cambridge Crystallographic Data Centre. https://doi.org/10.5517/cc12mn6ken
dc.relation.isSupplementedByDOI:10.5517/cc12mn6ken
dc.relation.isSupplementedByHANDLE:http://hdl.handle.net/10754/624318en
dc.relation.isSupplementedByAhmed, S. M., Poater, A., Childers, M. I., Widger, P. C. B., LaPointe, A. M., Lobkovsky, E. B., … Cavallo, L. (2014). CCDC 1001989: Experimental Crystal Structure Determination [Data set]. Cambridge Crystallographic Data Centre. https://doi.org/10.5517/cc12mn7len
dc.relation.isSupplementedByDOI:10.5517/cc12mn7len
dc.relation.isSupplementedByHANDLE:http://hdl.handle.net/10754/624319en
All Items in KAUST are protected by copyright, with all rights reserved, unless otherwise indicated.