SURFACE ORGANOMETALLIC CHEMISTRY - REACTIVITY OF SILICA-BOUND RHODIUM ALLYL COMPLEXES AND THE GENESIS OF HIGHLY DISPERSED SUPPORTED RHODIUM CATALYSTS

[[abstract]]The surface organometallic chemistry of silica-supported diallylrhodium, (SiJ-O-Rh(allyl)2 ((Si) is used to indicate surface Si), was characterized by 'H NMR, IR, and XP spectroscopy. The complex was reduced by H2 under mild conditions, with the elimination of propene, to give highly dispersed rhodium metal aggregates. Reaction of the surface with CO led to the formation of Rhl(CO)* species, formed not from the {SipRh(allyl)2 groups but from other groups, presumably incorporating Rh(II1) ions. The reaction of (SipRh(allyl), with hydrogen was inhibited by CO bonded to these other Rh centers. Evidently the reduction of the diallyl groups by hydrogen proceeded via reduction of Rh(II1) ions with spillover of hydrogen to the support, which led to further protolysis of (Si)-O-Rh(allyl)2 and eventually to rhodium metal. The small metal aggregates, observed by transmission electron microscopy, were catalytically active for toluene hydrogenation[[fileno]]2010323010094[[department]]化學