- Electron Paramagnetic Resonance Study of the Reactivity toward Carbon Monoxide and Oxygen of O- Ions Adsorbed on Silica-supported Molybdenum Catalysts
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Using the e.p.r. technique, the reaction at 77 K of an O- radical, formed by N2O adsorption on reduced MoO3/SiO2 samples, with CO or 13CO was followed, and possible to detect a CO2- radical (g1=2.0029, g2=2.0016, g3=1.9974, A1=199 G, A2=240 G, A3=207 G) which was stable at room temperature.This species reacted with O2 at 77 K to give rise to a radical of the type (O2COO)- (g1=2.0486, g2=2.0078, g3=2.0026, A1C=OG, A2C=4.8 G, A3C=6 G, A3O1=104 G, A3O11=40 G).At 150 K, it disappeared irreversibly, generating an O2- radical (g1=2.0175, g2=2.0097, g3=2.0040, A3O1=80 G, A3O11=70 G) similar to that formed by direct adsorption of oxygen on reduced MoO3/SiO2.
- Gonzalez-Elipe, Agustin R.,Louis, Catherine,Che, Michel
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- Crystal structure and solution dynamics of (μ-H)Os3(CO)10(μ-η2-CPh=CHPh)
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The hydridostilbenyl complex HOs3(CO)10(CPh=CHPh) has been synthesized from the reaction of H2Os3(CO)10 with excess diphenylacetylene at room temperature. The molecular structure of the stilbenyl complex is reported and compared to the structures of other alkenyltriosmium complexes. Crystals of HOs3(CO)10(CPh=CHPh) form in the space group P212121 with a = 11.521 (2) ?, b = 14.244 (2) ?, c = 31.695 (4) ?, V = 5201.3 (10) ?3, ρ(obsd) = 2.64 (2) g cm-3, ρ(calcd) = 2.633 g cm-3, for mol wt 1031.0 and Z = 8. The molecule contains a triangular array of osmium atoms with the stilbenyl ligand bridging the Os(1)-Os(2) edge and forming a σ bond to Os(2) and a π bond to Os(1). All carbonyl ligands are terminally bound; Os(1) and Os(2) each have three carbonyls, whereas Os(3) has four carbonyls. The presence of a bridging hydride along the Os(1)-Os(2) edge was not detected directly but was supported by analysis of the carbonyl bond angles. The orientation of the alkenyl ligand in HOs3(CO)10(CPh=CHPh) differs from that observed in the previously characterized alkenyl compounds HOs3(CO)10(CH=CHR) (R = H, Et). The vinyl derivatives have been shown to have a structure in which Os(3) is syn with respect to the hydrogen atom on the α-carbon of the ligand. In contrast, the stilbenyl ligand is positioned so that Os(3) is anti with respect to the substitutent on the α-carbon, which in this case is a phenyl group. Variable-temperature 13C NMR spectra of the carbonyl resonances of HOs3(CO)10(CPh=CHPh) revealed that the stilbenyl ligand is fluxional. The spectral behavior observed is consistent with a mechanism involving a facile interchange of the σ and π bonds between the bridged osmium atoms. Similar fluxional behavior was observed previously for the vinyl derivatives. The activation barrier (ΔG?c) for this rearrangement in the case of the stilbenyl ligand was found to be 11.3 kcal/mol compared to 10.3 kcal/mol for the vinyl ligand in HOs3(CO)10(CH=CH2).
- Clauss,Tachikawa,Shapley,Pierpont
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p. 1528 - 1533
(2008/10/08)
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