Tuning acid-base cooperativity to create next generation silica-supported organocatalysts

Catalysts incorporating acid and base cooperative interactions can more efficiently catalyze the aldol and nitroaldol reactions than single component catalysts since cooperative interactions enable activation of both reaction partners. Both homogeneous and heterogeneous catalysis studies demonstrate that limiting acid-base interactions is important and can be achieved by using weak acids (including surface silanols of heterogeneous catalysts) or using a rigid backbone between the acid and base. For heterogeneous catalysts, cooperativity between amines and silanols can be tuned by controlling the alkyl linker length of the aminosilane and controlling the silica support pore size. The nitroaldol condensation is more sensitive to these parameters than the aldol condensation, resulting in an order of magnitude difference in reaction rates when varying these two parameters. While knowledge of the amine-silanol cooperativity is still limited, these findings demonstrate useful structure-property trends that can be used to design more efficient bio-inspired catalysts. (C) 2013 Elsevier Inc. All rights reserved.