Silica-surface reorganization during organotin grafting evidenced by 119Sn DNP SENS: a tandem reaction of gem-silanols and strained siloxane bridges

Abstract

Grafting reactive molecular complexes on dehydroxylated amorphous silica is a strategy to develop “single-site” heterogeneous catalysts. In general, only the reactivity of isolated silanols is invoked for silica dehydroxylated at 700 °C ([SiO_2-700]), though ca. 10% of the surface silanols are in fact geminal Q₂-silanols. Here we report the reaction of allyltributylstannane with [SiO_2-700] and find that the geminal Q₂-silanols react to form products that would formally arise from vicinal Q₃-silanols that are not present on [SiO_2-700], indicating that a surface rearrangement occurs. The reorganization of the silica surface is unique to silica dehydroxylated at 700 °C or above. The findings were identified using Dynamic Nuclear Polarization Surface Enhanced NMR Spectroscopy (DNP SENS) combined with DFT calculations.