Silica-supported rhodium hydrides stabilized by triisopropylphosphine

The reaction of the silica-supported complex (dropSiO)(dropSiOX)Rh(eta(3)-C3H5)(2), where X is H or Si, with excess (PPr3)-Pr-i leads to the formation of the chemisorbed bis(phosphine) Rh(I) complex [dropSiORh((PPr3)-Pr-i)(2)](x), proposed to be dimeric (x = 2) on the basis of the P-31 MAS NMR spectrum. The phosphine complex irreversibly binds H-2 to give a hydride complex, dropSiORh((PPr3)-Pr-i)(2)(H)(2), characterized by IR and P-31 MAS NMR spectroscopy as well as D-exchange. The coordinatively unsaturated hydride complex is inferred to be the active site for hydrogenation of olefins under mild conditions. (C) 2003 Elsevier Science B.V. All rights reserved.