title: Mechanistic basis for high reactivity of (salen)Co-OTs in the hydrolytic kinetic resolution of terminal epoxides.
abstract: The (salen)Co(III)-catalyzed hydrolytic kinetic resolution (HKR) of terminal epoxides is a bimetallic process with a rate controlled by partitioning between a nucleophilic (salen)Co-OH catalyst and a Lewis acidic (salen)Co-X catalyst. The commonly used (salen)Co-OAc and (salen)Co-Cl precatalysts undergo complete and irreversible counterion addition to epoxide during the course of the epoxide hydrolysis reaction, resulting in quantitative formation of weakly Lewis acidic (salen)Co-OH and severely diminished reaction rates in the late stages of HKR reactions. In contrast, (salen)Co-OTs maintains high reactivity over the entire course of HKR reactions. We describe here an investigation of catalyst partitioning with different (salen)Co-X precatalysts and demonstrate that counterion addition to epoxide is reversible in the case of the (salen)Co-OTs. This reversible counterion addition results in stable partitioning between nucleophilic and Lewis acidic catalyst species, allowing highly efficient catalysis throughout the course of the HKR reaction.
authors.affiliation: Department of Chemistry & Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Lars P C
authors.initials: LP
authors.lastname: Nielsen
authors.forename: Stephan J
authors.initials: SJ
authors.lastname: Zuend
authors.forename: David D
authors.initials: DD
authors.lastname: Ford
authors.forename: Eric N
authors.initials: EN
authors.lastname: Jacobsen
mesh_terms: D003035:Cobalt / Q000737:chemistry*; D004852:Epoxy Compounds / Q000737:chemistry*; D005029:Ethylenediamines / Q000737:chemistry*; D006868:Hydrolysis; D007700:Kinetics; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*
chemical_list: D004852:Epoxy Compounds; D005029:Ethylenediamines; D009942:Organometallic Compounds; D003035:Cobalt; C011452:disalicylaldehyde ethylenediamine