Bifunctional mesoporous silica catalyst for C-C bond forming tandem reactions

We 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/Pd^II-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.