Surface Organometallic Chemistry on Oxides: Reaction of Trimethylphosphine with Bis(allyl)rhodium Grafted onto Silica

Abstract

The reaction of Rh(η3-C3H5)3 with the surface hydroxyl groups of partially dehydroxylated silica leads to the formation of the surface organometallic complex (≡SiO)(≡SiOX)Rh(η3-C3H5) 2, 1 (where X is H or Si≡), with evolution of propene. The reaction of 1 with PMe3 was examined, and two major pathways were discovered. Reductive elimination of two allyl ligands as 1,5-hexadiene and coordination of PMe3 give the surface product (≡SiO)Rh(PMe3)3, 2, which was characterized by elemental analysis, IR and 31P MAS NMR spectroscopy. We also prepared 2 independently from CH3Rh(PMe3)3 and partially dehydroxylated silica. The second major reaction pathway is the elimination of propene to give (≡SiO)2Rh(η1-C3H 5)(PMe3)3, 3. The presence of the σ-bound allyl ligand was inferred from its characteristic IR spectrum. The reactivity of 3 toward CO was examined: insertion of CO into the Rh-C bond followed by reductive elimination of the silyl ester =SiOC(O)C3H5 produces (≡SiO)Rh(CO)(PMe3)2, 4. In static vacuum, 3 decomposes to give allyl alcohol, which is slowly decarbonylated by 2.