Nitroaldol reactions catalyzed by amine-MCM-41 hybrids

The catalytic properties of several amine-functionalized MCM-41 materials in the nitroaldol (Henry) reaction are reported. The work investigated the effects of organoamine type (primary, secondary, tertiary), amine density, and the presence of silanol groups on the catalytic activity and product selectivity. High selectivity to the nitroalcohol product was achieved by introducing secondary and tertiary amine groups on the MCM-41 surface, while the nitroalkene is the dominant product for primary amines. Steric effects appear to be significant in determining the overall reactivity as the least sterically hindered amines are the most active. The capping of silanols with trimethylsilyl groups resulted in a reduction in catalytic activity for nearly all samples, indicating the importance of surface silanols and/or the surface polarity in the reaction.