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Keywords:

  • cobalt;
  • kinetic resolution;
  • metalation;
  • polymers;
  • supported catalysts

Abstract

Regioselective ring opening of 1,2-epoxyhexane with methanol can be catalyzed by CoIII–salen complexes, whereas related CoII complexes are inactive species in this and other epoxide ring-opening reactions. In this work, Co–salen complexes supported on a highly cross-linked polymer resin are synthesized, characterized, and utilized as catalysts for the ring-opening of 1,2-epoxyhexane with methanol. By manipulating the metalation degree of a polymeric resin containing salen ligands, Co salen catalysts are immobilized on various batches of the same polymeric support with different Co densities. The supported catalysts are shown to have different turnover frequencies on a CoIII basis in the reaction, with the rates correlating with the overall cobalt content rather than the CoIII content alone. The observation that both CoIII and CoII salen species play a role in the reaction has not yet been observed to occur in other epoxide ring-opening systems studied to date, and the results here demonstrate the reaction to kinetically be approximately 0.1 order in CoII species. Catalyst recycling studies imply that both cobalt and counter-anion leaching account for the catalyst deactivation.