Wednesday, August 6, 2014

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


Conley, M.P., et al., Silica-surface reorganization during organotin grafting evidenced by 119Sn DNP SENS: a tandem reaction of gem-silanols and strained siloxane bridges. Phys. Chem. Chem. Phys., 2014. 16(33): p. 17822-17827.

http://dx.doi.org/10.1039/C4CP01973C

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 [degree]C ([SiO2-700]), though ca. 10% of the surface silanols are in fact geminal Q2-silanols. Here we report the reaction of allyltributylstannane with [SiO2-700] and find that the geminal Q2-silanols react to form products that would formally arise from vicinal Q3-silanols that are not present on [SiO2-700], indicating that a surface rearrangement occurs. The reorganization of the silica surface is unique to silica dehydroxylated at 700 [degree]C or above. The findings were identified using Dynamic Nuclear Polarization Surface Enhanced NMR Spectroscopy (DNP SENS) combined with DFT calculations.