title: Self-assembly approach toward chiral bimetallic catalysts: bis-urea-functionalized (salen)cobalt complexes for the hydrolytic kinetic resolution of epoxides.
abstract: A series of novel bis-urea-functionalized (salen)Co complexes has been developed. The complexes were designed to form self-assembled structures in solution through intermolecular urea-urea hydrogen-bonding interactions. These bis-urea (salen)Co catalysts resulted in rate acceleration (up to 13 times) in the hydrolytic kinetic resolution (HKR) of rac-epichlorohydrin in THF by facilitating cooperative activation, compared to the monomeric catalyst. In addition, one of the bis-urea (salen)Co(III) catalyst efficiently resolves various terminal epoxides even under solvent-free conditions by requiring much shorter reaction time at low catalyst loading (0.03-0.05 mol %). A series of kinetic/mechanistic studies demonstrated that the self-association of two (salen)Co units through urea-urea hydrogen bonds was responsible for the observed rate acceleration. The self-assembly study with the bis-urea (salen)Co by FTIR spectroscopy and with the corresponding (salen)Ni complex by (1)H NMR spectroscopy showed that intermolecular hydrogen-bonding interactions exist between the bis-urea scaffolds in THF. This result demonstrates that self-assembly approach by using non-covalent interactions can be an alternative and useful strategy toward the efficient HKR catalysis.
authors.affiliation: Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA.
authors.forename: Jongwoo
authors.initials: J
authors.lastname: Park
authors.forename: Kai
authors.initials: K
authors.lastname: Lang
authors.forename: Khalil A
authors.initials: KA
authors.lastname: Abboud
authors.forename: Sukwon
authors.initials: S
authors.lastname: Hong
mesh_terms: D002384:Catalysis; D003035:Cobalt / Q000737:chemistry*; D004852:Epoxy Compounds / Q000737:chemistry*; D005029:Ethylenediamines / Q000737:chemistry*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D014508:Urea / Q000737:chemistry*
chemical_list: D004852:Epoxy Compounds; D005029:Ethylenediamines; D009942:Organometallic Compounds; D003035:Cobalt; D014508:Urea; C011452:disalicylaldehyde ethylenediamine