The adsorption of molecular species on oxide surfaces represents the crucial first step in many synthetic processes and purification procedures. Solid-phase synthesis, chromatography, ion exchange, or catalysis are typical fields involved. Here, we present new, surprisingly general and common characteristics regarding the surface mobilities and phase transitions of species as diverse as phosphines, phosphine oxides, and metallocenes, when they are adsorbed on silica surfaces. The nature and mobility of each adsorbed species is optimally investigated by multinuclear solid-state NMR spectroscopy. Classical 31P and 13C CP/MAS (Cross-Polarization/Magic Angle Spinning) and 2H MAS investigations of dry materials, as well as HRMAS NMR (High-Resolution MAS) of slurries, reveal the CSA (Chemical Shift Anisotropy), the chemical shift, the quadrupolar coupling constant, and the residual halfwidth, on going from the molecular crystalline to the adsorbed species. Interestingly, the adsorption can be achieved in all cases not only from solution, but also by grinding together the dry components (with high melting points!), phosphines, phosphine oxides, and metallocenes, with silica. Surprising quantitative insights about the diverse modes of mobility on the silica surface will be presented for all adsorbed species.

Phenomena observed in solid-state NMR spectroscopy when adsorbing phosphines, phosphine oxides, and metallocenes on silica surfaces

247th National Meeting (2014)

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