Silica-Supported, Single-Site Sc and Y Alkyls for Catalytic Hydrogenation of Propylene

Single-site Sc and Y on silica catalysts have been prepared by aqueous and organometallic grafting methods. The former yields Y(III) ions with five bonds at an average bond distance of 2.31 A by X-ray absorption spectroscopy. Although the aqueous synthesis gave single-site Y with low coordination number, these were not catalytic for alkane dehydrogenation or olefin hydrogenation. Single-site Sc(III) and Y(III) species were also prepared by grafting Sc(CH2Si(CH3)3)3(THF)2 and Y(CH2Si(CH3)3)3(THF)2, respectively, and these are catalysts for olefin hydrogenation at temperatures from about 60 to 100 °C; however, they were thermally unstable at higher temperatures necessary for alkane dehydrogenation. The structure of the grafted Y complex was determined by X-ray absorption spectroscopy, IR, and NMR. Grafting led to protonolysis of two of the three CH2Si(CH3)3 ligands. Additionally, there was loss of one THF ligand. The EXAFS indicated that there were four Y–ligand bonds in the surface species, two at 2.16 A a...