Surface Organometallic Chemistry of Titanium on Silica−Alumina and Catalytic Hydrogenolysis of Waxes at Low Temperature

Abstract

Ti(CH2tBu)4 (1) reacts selectively with the surface silanols of a silica−alumina partially dehydroxylated at 500 °C to provide the monosiloxy species [(≡SiO)Ti(CH2tBu)3]SA (2a) and the bisiloxy species [(≡SiO)2Ti(CH2tBu)2]SA (2b) in a ca. 40:60 ratio, with concomitant evolution of 1.6 ± 0.2 equiv of neopentane per Ti. These surface complexes were characterized via the combined use of several techniques such as IR spectroscopy, 1H MAS, 13C-CP/MAS, 2D 1H−13C HETCOR, and J-resolved solid-state NMR, as well as mass balance analysis. By treatment under hydrogen at 150 °C the neopentyl ligands in complexes 2a,b undergo hydrogenolysis and a mixture of supported titanium species is obtained. IR, ESR, 1H MAS, and DQ solid-state NMR spectroscopies show the presence of ca. 3% [(≡SiO)(MsO)TiH2]SA (3a; Ms = Si, Al), 5% [(≡SiO)(MsO)Ti(Me)−H]SA (3b), 75−80% [(≡SiO)(MsO)2Ti−H]SA (3c), and 14% [(≡SiO)(MsO)2TiIII]SA (3d), along with (SiHx) and (AlHx) fragments whose formation arise from the opening of adjacent Si−O−M bridg...