Mesocellular foam-supported catalysts: Enhanced activity and recyclability for ring-closing metathesis

Although ring-closing metathesis (RCM) has been one of the most powerful methodologies for creating cyclic compounds, the pharmaceutical industry has not yet widely adopted this process commercially due to the high costs and leaching problems of homogeneous ruthenium catalysts. To circumvent these problems, we have immobilized the second-generation Hoveyda-Grubbs catalyst effectively onto siliceous mesocellular foam (MCF). The open and interconnected pores of MCF facilitated ligand immobilization and substrate diffusion. We ave observed that the ligand and metal loadings significantly affected the catalytic activity and recyclability. Enhanced recyclability by suppression of ruthenium leaching was achieved by using excess immobilized ligands. The resulting novel heterogenized catalysts demonstrated excellent activity and reusability for the RCM of various types of substrates.