SURFACE ORGANOMETALLIC CHEMISTRY ON OXIDES - REACTION OF TRIMETHYLPHOSPHINE WITH BIS(ALLYL)RHODIUM GRAFTED ONTO SILICA

The reaction of Rh(eta(3)-C3H5)(3) With the surface hydroxyl groups of partially dehydroxylated silica leads to the formation of the surface organometallic complex (=SiO)(=SiOX)Rh(eta(3)-C3H5)(2), 1 (where X is H or Si=), with evolution of propene. The reaction of 1 with PMe(3) w as examined, and two major pathways were discovered. Reductive elimina tion of two allyl ligands as 1,5-hexadiene and coordination of PMe(3) give the surface product (=SiO)Rh(PMe(3))(3), 2, which was characteriz ed by elemental analysis, IR and P-31 MAS NMR spectroscopy. We also pr epared 2 independently from CH3Rh(PMe(3))(3) and partially dehydroxyla ted silica. The second major reaction pathway is the elimination of pr opene to give (=SiO)(2)Rh(eta(1)-C3H5)(PMe(3))(3), 3. The presence of the sigma-bound allyl ligand was inferred from its characteristic IR s pectrum. The reactivity of 3 toward CO was examined: insertion of CO i nto the Rh-C bond followed by reductive elimination of the silyl ester =SiOC(O)C3H5 produces (=SiO)Rh(CO)(PMe(3))(2), 4. In static vacuum, 3 decomposes to give allyl alcohol, which is slowly decarbonylated by 2 .