Cooperative Acid-Base Effects with Functionalized Mesoporous Silica Nanoparticles: Applications in Carbon-Carbon Bond-Formation Reactions

Acid-base bifunctional mesoporous silica nanoparticles (MSN) were prepared by a one-step synthesis by co-condensation of tetraethoxysilane (TEOS) and silanes possessing amino and/or sulfonic acid groups. Both the functionality and morphology of the particles can be controlled. The grafted functional groups were characterized by using solid-state Si-29 and C-13 cross-polarization/magic angle spinning (CP/MAS) NMR spectroscopy, thermal analysis, and elemental analysis, whereas the structural and the morphological features of the materials were evaluated by using XRD and N-2 adsorption-desorption analyses, and SEM imaging. The catalytic activities of the mono-and bifunctional mesoporous hybrid materials were evaluated in carbon-carbon coupling reactions like the nitroaldol reaction and the one-pot deacetalization-nitroaldol and deacetalization-aldol reactions. Among all the catalysts evaluated, the bifunctional sample containing amine and sulfonic acid groups (MSN-NNH2-SO3H) showed excellent catalytic activity, whereas the homogeneous catalysts were unable to initiate the reaction due to their mutual neutralization in solution. Therefore a cooperative acid-base activation is envisaged for the carbon-carbon coupling reactions.