On the Stability and Recyclability of Supported Metal-Ligand Complex Catalysts: Myths, Misconceptions and Critical Research Needs

Research on heterogenized metal complex catalysts has been carried out for 40 years. Despite thousands of published catalysts, there are only two significant commercial processes that utilize supported metal complex catalysts. Most academic papers are simply demonstration of concept studies reporting myriad ways to support various metal complex catalysts. Too few papers focus on rigorous studies of reaction kinetics, catalyst recycle, catalyst stability and deactivation pathways. Here, preliminary stability and deactivation studies of supported enantioselective Co-salen epoxide ring-opening catalysts and enantioselective Ru-salen olefin cyclopropanation catalysts are summarized. Insights with regard to catalyst deactivation suggest methodologies for catalyst stabilization, allowing for more effective catalyst recycle and enhanced catalyst turnover. Further examples where supported metal complex catalysts are applied in commercial processes will require the field to shift focus from demonstration of concept studies to more detailed investigations of catalyst stability and recyclability.