Atomic-level organization of vicinal acid–base pairs through the chemisorption of aniline and derivatives onto mesoporous SBA15†
The design of novel heterogeneous catalysts with multiple adjacent functionalities is of high interest to heterogeneous catalysis. Herein, we report a method to obtain a majority of bifunctional acid–base pairs on SBA15. Aniline reacts with SBA15 by opening siloxane bridges leading to N-phenylsilanamine–silanol pairs. In contrast with ammonia treated surfaces, the material is stable under air/moisture. Advanced solid state MAS NMR (2D 1H–1H double-quantum, 1H–13C HETCOR) experiments and dynamic nuclear polarization enhanced 29Si and 15N spectra demonstrate both the close proximity between the two moieties and the formation of a covalent Si–N surface bond and confirm the design of vicinal acid–base pairs. This approach was successfully applied to the design of a series of aniline derivatives of bifunctional SBA15. A correlation between the substituent effects on the aromatic ring (Hammett parameters) with the kinetics of a model Knoevenagel reaction is observed.