932382-45-1Relevant articles and documents
Influence of the initial bonding mode of the hydrocarbyl bridge on the mechanisms and products of the electrochemical reduction of alkyne- and vinylidene dimolybdenum tris(μ-thiolate) complexes
Le Goff, Alan,Le Roy, Christine,Petillon, Francois Y.,Schollhammer, Philippe,Talarmin, Jean
, p. 265 - 276 (2008/02/02)
The electrochemical reduction of isomeric complexes, [Mo2Cp 2(μ-SMe)3(μ-η1:η1- HCCPh)]+ (1+) and [Mo2Cp2(μ-SMe) 3(μ-η1:η2-C*CHPh)] + (3+), where the hydrocarbyl bridges in a η1:η1- or a η1:η2 mode, has been studied by cyclic voltammetry and controlled-potential electrolysis in thf-[NBu4][PF6] and CH2Cl 2-[NBu4][PF6], in the absence and in the presence of acid. The binding mode of the CC fragment induces different electrochemical behaviour of the complexes in acid-free solutions since 1 + reduces in two diffusion-controlled one-electron steps while the first reduction of 3+ is characterized by slow electron transfer kinetics. Controlled-potential reduction of both 1+ and 3+ produces a mixture of the acetylide [Mo2Cp2(μ-SMe) 3(μ-η1:η2-CCPh)] (2) and alkylidyne complexes [Mo2Cp2(μ-SMe)3(μ- η1-CCH2Ph)] (4). In the presence of acid, the electrochemical reduction of 1+ and of 3+ occurs according to ECE processes. The nature of the products formed by controlled-potential reduction of 1+ depends on the nature of the acid and of the solvent. The transient formation of a complex with a μ-alkenyl ligand, either [Mo2Cp2(μ-SMe)3(μ-η1: η2-CH*CHPh)] (7) or an isomer, is suggested by the oxidative electrochemistry of 7 and by its reaction with acids. In thf-[NBu 4][PF6] in the presence of an excess of acid (HBF 4/Et2O) and of phenylacetylene, electrolysis of 1 + gives rise to catalytic reduction of phenylacetylene to styrene. However, unidentified reactions limit the efficiency of this process. The reduction of 3+ in acidic medium produces the alkyl complex [Mo 2Cp2(μ-SMe)3(μ-CH2CH 2Ph)] (6) through alkylidyne [Mo2Cp2(μ-SMe) 3(μ-η1-CCH2Ph)] (4) and alkylidene [Mo2Cp2(μ-SMe)3(μ-η1- CHCH2Ph)]+ (5+) intermediates. Some ethylbenzene was formed after reduction of 5+ in the presence of acid. These results show an effect of the binding mode of the hydrocarbyl bridge on the mechanism and products of the reduction of the corresponding complexes. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
