Bifunctional Mesoporous Silica Catalyst for C–C Bond Forming Tandem Reactions

Abstract

AbstractWe report on the synthesis and catalytic properties of a class of hybrid organic–inorganic mesoporous bifunctional heterogeneous catalysts for efficient catalysis of two‐step tandem reactions in one pot. With a solvent‐assisted grafting method, two different catalytic groups, that is, an organoamine and a palladium–organodiamine complex, were immobilized onto high‐surface‐area mesoporous silica sequentially, by using their corresponding organosilanes in 2‐propanol or toluene as the solvent in the first step and toluene as the solvent in the second step. Both MCM‐41 and SBA‐15 mesoporous silicas were used as support materials for the two catalytic groups, and the effect of different sequential grafting of the two organosilanes in 2‐propanol or toluene on the structures and the catalytic properties of the resulting bifunctional catalysts were investigated. By using the resulting amine/PdII–diamine bifunctional mesoporous material as catalyst, the occurrence of two very important C–C bond forming reactions, that is, the Sonogashira and the Henry reactions, was demonstrated in one pot for the first time. Yields of approximately 100 % in 2.5 h for the Sonogashira reaction and approximately 100 % in 45 min for the Henry reaction were obtained in the presence of the bifunctional catalyst when the reactions were run individually. When the bifunctional catalyst was used to catalyze the Sonogashira–Henry reactions in tandem in one pot, a yield of up to approximately 60 % of the Sonogashira–Henry product in 5 h was obtained. The synthesis and use of such bifunctional catalysts for efficient catalysis of the tandem reaction is of importance in three significant ways: it prevents the unnecessary use of solvents and other chemicals required for the purification of the intermediate products of either individual reaction, eliminates some of the work‐up procedures, and lowers the cost of synthesis of the final product.