Surface organometallic chemistry on metals: Influence of organometallic fragments grafted to the surface of Rh particles on the competitive hydrogenation of terminal and internal double bonds of unsaturated primary alcohols

Hydrophobic organotin fragments, grafted to the surface of a rhodium particle can strongly modify the rate of the hydrogenation of internal or terminal carbon-carbon (C-C) double bonds of unsaturated primary alcohols. In this work, the rate of hydrogenation of trans-2-hexenol and 5-hexenol was determined at room temperature under 20 bar of hydrogen in butanol + water (30 + 10) solution for Rh/SiO₂ catalysts which were either used unmodified or modified with Sn(n-C₄H₉)₄. It was found that the presence of alkyl groups decreases the ratio between the rate of hydrogenation of the terminal and internal double bond by a factor of 4. These results are explained by the formation of a hydrophobic layer around the modified particle which inhibits the adsorption of the unsaturated alcohol by its internal double bond.