A stable Copper-Modified silica microsphere catalyst for the synthesis of N-substituted carbazoles and organosilanes

Carbenes are key precursors for various transformations and are applied broadly in the synthesis of complex molecules and drug. Typically, such transformations require expensive metal and complex ligands, leading to a vigorous reaction system and trace metal residues. Herein, we report copper-modified silica microspheres (SM-b) as heterogeneous catalyst in the insertion reaction of diazo compounds with carbazole and silanes. Under this strategy, the optimal SM-b catalyst can prevent the reaction from being too vigorous and can be reused in continuous reactions. Furthermore, gram-scale and catalyst recycling reactions have been proven as the potential industrial applications of the SM-b catalysts. Inductively coupled plasma analysis revealed a residual copper content of only 6.25 ppm in the reaction solution and no detectable copper in the final product, indicating that the residual metal content of the product is far below the FDA-imposed limit of metal impurities.