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Manganese Catalysts with Molecular Recognition Functionality for Selective Alkene Epoxidation
journal contributionposted on 2009-01-19, 00:00 authored by Jonathan F. Hull, Effiette L. O. Sauer, Christopher D. Incarvito, J. W. Faller, Gary W. Brudvig, Robert H. Crabtree
Selective epoxidation of alkenes is possible with a new manganese porphyrin catalyst, CPMR, that uses hydrogen bonding between the carboxylic acid on the substrate molecule and a Kemp’s triacid unit. For two out of three olefin substrates employed, molecular recognition prevents the unselective oxidation of C−H bonds, and directs oxidation to the olefin moiety, giving only epoxide products. Weak diastereoselectivity is observed in the epoxide products, suggesting that molecular recognition affects the orientation of the catalyst-bound substrate. The previously reported manganese terpyridine complex CTMR is shown to be a superior epoxidation catalyst to the porphyrin catalyst CPMR. Good conversion of 2-cyclopentene acetic acid (substrate S2) with CPMR is consistent with molecular modeling, which indicates a particularly good substrate/catalyst match. Evidence suggests that hydrogen bonding between the substrate and the catalyst is critical in this system.