Selective Activation of CH Bonds in Polar Vinyl Olefins and Coupling of Ethylene to the Activated Carbon Atoms in Pentaruthenium Complexes.

Abstract

Ru5(μ5-C)(CO)15, 1, has been found to activate CH bonds in the vinyl group of polar vinyl olefins, methyl acrylate (MA), and vinyl acetate (VAc), through a cluster opening process to yield the complexes Ru5(μ5-C)(CO)14[η2-O═C(OMe)CH═CH](μ-H), 2, and Ru5(μ5-C)(CO)14[η2-(MeCO2)C═CH2](μ-H), 4, respectively. The site of CH activation is dependent on the olefin substituent. In 2, the site of CH activation is the β-carbon atom of the vinyl group, while in 4 the CH activation has occurred exclusively at the α-carbon atom of the vinyl group. Compound 2 can be further decarbonylated to yield the complex Ru5(μ5-C)(CO)13[μ-η3-O═C(OMe)CHCH](μ-H), 3, which contains a η3-bridging acryloyl ligand. Compound 2 reacts with ethylene in the presence of Me3NO to yield three new Ru5 products: Ru5(μ5-C)(CO)13[η4-1- anti,3- syn-{O═C(OMe)}C(H)C(H)C(H)Me](μ-H), 5, Ru5(μ5-C)(CO)12(C2H4)[μ-η3- O═C(OMe)C(H)C(H)](μ-H), 6, and Ru5(μ5-C)(CO)13[η4- anti-O═C(OMe)H2CHCHCH2](μ-H), 7. Compounds 5 and 7 are isomers containing substituted η3-allyl ligands formed by the coupling of the ethylene to the CH-activated β-carbon atom of the acryloyl ligand accompanied by some metal-mediated H-shifts. Compound 6 contains an uncoupled π-coordinated ethylene ligand. Compound 7 was isomerized to 5 thermally at 80 °C. Compound 4 reacts with ethylene in the presence of Me3NO to yield two new Ru5 products: Ru5(μ5-C)(CO)13[η4-1,1- anti- syn-[(O2CMe)C(Me)CHCH2](μ-H), 8, and Ru5(μ5-C)(CO)13[η4-1- anti-CH(Me)C(O2CMe)(CH2)](μ-H), 9. Compounds 8 and 9 both contain substituted η3-allyl ligands formed by the coupling of the ethylene to the CH-activated α-carbon atom of the vinyl acetyl ligand. Compound 8 was isomerized to 9 thermally at 80 °C. All new products were characterized structurally by single-crystal X-ray diffraction analyses.