日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

This study investigates the influence of mesoporous silica pore size on catalytic activity in allylation and 1,4-addition reactions using supported metal complex catalysts. A diphosphine palladium complex (PP-Pd) immobilized on mesoporous silica exhibited enhanced activity in the allylation of a ketoester with allyl alcohol. The hydroxyl groups on the silica surface played a cooperative role with Pd species, facilitating substrate activation. Notably, kinetic studies revealed that mesoporous silica with a pore size of approximately 23 Å showed the highest activity, attributed to optimized molecular interactions and substrate accumulation within the pores. In addition, the study evaluated 1,4-addition of phenylboronic acid using Rh complexes co-immobilized with octyl groups to modulate pore hydrophobicity. Under aqueous conditions, increasing the proportion of octyl chains improved catalytic performance, indicating that higher local hydrophobicity around the Rh center reduced water interference and improved substrate access. This hydrophobic tuning was most effective with smaller pore sizes, where confinement intensified the water-shielding effect. Overall, the results highlight the importance of controlling pore size and surface functionality in mesoporous silica supports to enhance cooperative catalysis and optimize reaction environments. These findings offer valuable insights for the rational design of heterogeneous catalysts in fine chemical synthesis.