Bifunctional phosphines immobilized on inorganic oxides

The bifunctional phosphine Ph2P(CH2)(3)Si(OEt)(3) has been immobilized on M gO, TiO2, Al2O3, and SiO2 surfaces. The materials were studied by Al-27 MAS , Si-29 CP/MAS, (31)p CP/MAS, and P-31 suspension NMR spectroscopy. MgO and TiO2 cannot bind the phosphine strongly, so persistent leaching occurs. Al 2O3 was applied in the basic, neutral, and acidic versions. All of them nee ded extensive washing, and leaching of the phosphine was found for acidic A l2O3. With alumina and silica as the supports, the half-widths and chemical shifts of the 31p suspension NMR signals of the phosphine have been determ ined in order to investigate the mobilities of the phosphine moieties. Here by the surface coverages, suspension media, acidities, and pore diameters h ave been varied. While the pore diameters (40-100 Angstrom) and acidities h ave 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 phosph ine molecules, when their packing on the surface gets denser. With respect to leaching and convenience of handling, SiO2 turned out to be the most fav orable support for immobilizing phosphines.