Bifunctional phosphines immobilized on inorganic oxides
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abstract
The bifunctional phosphine Ph2P(CH2)3Si(OEt)3 has been immobilized on MgO, TiO2, Al2O3, and SiO2 surfaces. The materials were studied by 27Al/MAS, 29Si CP/MAS, 31p Cp/MAS, and 31P suspension NMR spectroscopy. MgO and TiO2 cannot bind the phosphine strongly, so persistent leaching occurs. Al2O3 was applied in the basic, neutral, and acidic versions. All of them needed extensive washing, and leaching of the phosphine was found for acidic Al2O3. With alumina and silica as the supports, the half-widths and chemical shifts of the 31P suspension NMR signals of the phosphine have been determined in order to investigate the mobilities of the phosphine moieties. Hereby the surface coverages, suspension media, acidities, and pore diameters have been varied. While the pore diameters (40-100 ) and acidities have practically no influence on the signal line widths, increasing surface coverage leads to narrower lines for all supports. This was interpreted as the result of brush-type rather than blanket-type arrangement of the phosphine molecules, when their packing on the surface gets denser. With respect to leaching and convenience of handling, SiO2 turned out to be the most favorable support for immobilizing phosphines.
