Enhanced cooperativity through design: pendant Co(III)--salen polymer brush catalysts for the hydrolytic kinetic resolution of epichlorohydrin (salen=N,N'-bis(salicylidene)ethylenediamine dianion)

Chemistry. 2008;14(24):7306-13. doi: 10.1002/chem.200800532.

Abstract

The Co(III)--salen-catalyzed (salen=N,N'-bis(salicylidene)ethylenediamine dianion) hydrolytic kinetic resolution (HKR) of racemic epoxides has emerged as a highly attractive and efficient method of synthesizing chiral C(3) building blocks for intermediates in larger, more complex molecules. HKR reaction rates have displayed a second order dependency on the concentration of active sites, and thus researchers have proposed a bimetallic transition state for the HKR mechanism. Here we report the utilization of pendant Co(III)--salen catalysts on silica supported polymer brushes as a catalyst for the HKR of epichlorohydrin. The novel polymer brush architecture provided a unique framework for promoting site-site interactions as required in the proposed bimetallic transition state of the HKR mechanism. Furthermore, the polymer brushes mimic the environment of soluble polymer-based catalysts, whereas the silica support permitted facile recovery and reuse of the catalyst. The polymer brush catalyst displayed increased activities over the soluble Jacobsen Co--salen catalyst and was observed to retain its high enantioselectivities (>99 %) after each of five reactions despite decreasing activities. Analysis indicated decomposition of the salen ligand as an underlying cause of catalyst deactivation.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Catalysis
  • Cobalt / chemistry*
  • Epichlorohydrin / chemistry*
  • Ethylenediamines / chemistry*
  • Hydrolysis
  • Kinetics
  • Magnetic Resonance Spectroscopy
  • Microscopy, Electron, Transmission
  • Polymers / chemistry*
  • Spectrometry, Mass, Electrospray Ionization

Substances

  • Ethylenediamines
  • Polymers
  • Epichlorohydrin
  • Cobalt
  • disalicylaldehyde ethylenediamine