Catalytic C–H bond activation on silicon dioxide overlayers

The catalytic activation of hydrocarbon C–H bonds is a fundamental process in heterogeneous catalysis. Although C–H bonds are readily activated on certain metal surfaces, the nature of the catalytic sites is still not understood. Catalytic C–H bond activation with group VIII transition metals1–7 is commonly studied by hydrogen/deuterium (H/D) exchange reactions of saturated hydrocarbons with D2. These reactions have shown that the inter-conversion of II-allyl intermediates is the most facile process leading to polydeuteration on platinum and rhodium2–5. Planar surfaces are the most active for C–H activation4,5. Carbonaceous surface species on platinum6, palladium,7 and rhodium5 are not part of the active site nor do they interfere with hydrogenation or C–H activation reactions. Unfortunately, none of these numerous studies could reveal the nature of the active site or the mechanism of the initial C–H activation step. Here we present evidence that the surface of inert silica becomes catalytically active in the presence of a transition metal underlayer. The similar selectivity observed on such drastically different surfaces as silica and platinum indicates that the existence of a surface is more important than its chemical nature. These results provide new insight into the nature of C–H activation and lead the way to a novel class of well-defined catalysts based on transition metal underlayers. Our data suggest that the major action of transition metals in heterogeneous C–H activation catalysis is the activation of hydrogen and that the activated hydrogen represents the catalytically active site.