Influence of the Framework Topology on the Reactivity of Chiral Pyrrolidine Units Inserted in Different Porous Organosilicas

Abstract

Three families of organosiliceous materials with different structuration level, order, and textural properties (non-ordered, M41S, and SBA-15 type materials) were prepared incorporating in their structural framework chiral pyrrolidine units with variable content. Likewise, non-ordered mesoporous hybrid solids were obtained through a sol-gel process in a fluoride medium, while M41S and SBA-15 type materials were obtained through micellar routes in the presence of long-chain neutral surfactants or block copolymers. Thanks to appropriate characterization studies and catalytic tests for the Michael addition between butyraldehyde and β-nitrostyrene, we showed how the void shapes and sizes present in the structure of hybrid materials control the diffusion of reactants and products, as well as confine transition states and reactive intermediates. The best catalytic results, considering activity and enantioselectivity, were achieved in the presence of a non-ordered material, NOH-Pyr-5%, which exhibited the highest Brunauer-Emmett-Teller (BET) area, with a 96% yield and a 82% ee for the Michael adduct.

Active Base Hybrid Organosilica Materials based on Pyrrolidine Builder Units for Fine Chemicals Production

“…Different synthesis routes for the mesoporous-hybrid materials containing pyrrolidine builder units incorporated in the framework. [12] Chemical analysis (C, H, N, S) of the mesoporous hybrid materials showed that the organic content was higher when the amount of bis-silylated precursor (PyrSil) used in the synthesis process was more elevated (Table S1). The results confirmed that the extraction methodologies used to remove the internal surfactant molecules of hybrid materials with M41S and SBA-15 topologies were not completely effective.…”