Polymer Resin Supported Cobalt–Salen Catalysts: Role of Co(II) Salen Species in the Regioselective Ring Opening of 1,2‐Epoxyhexane with Methanol

Regioselective ring opening of 1,2-epoxyhexane with methanol can be catalyzed by Co-III-salen complexes, whereas related Co-II 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 Co-III basis in the reaction, with the rates correlating with the overall cobalt content rather than the Co-III content alone. The observation that both Co-III and Co-II 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 Co-II species. Catalyst recycling studies imply that both cobalt and counter-anion leaching account for the catalyst deactivation.