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Treatment of [Mo2(Cp)2(μ-SMe)3(MeCN)2]+ (1+) with NO3– or NO2– results in the conversion of one terminally bound acetonitrile ligand into an amidato bridge. The reaction produces [Mo2(Cp)2(μ-SMe)3{μ-η1,η1-OC(Me)NH}]0/+ (20/+) and involves the formation of an intermediate, which was detected by cyclic voltammetry but which could not be isolated, and which likely arises from the substitution of the NOx anion for one MeCN ligand. The electrochemical behaviour of 2+ was studied by cyclic voltammetry in THF and MeCN. The reduction of 2+ in the presence of acid (HBF4/H2O or HBF4/Et2O) in these solvents leads to the release of the amidate bridge. Controlled-potential electrolysis of 2+ in MeCN in the presence of acid produces 1+ quantitatively; the charge consumed (>1 F mol–1 of 1+) indicates that electrons are also used to reduce protons. This was confirmed by the formation of 2+ (in variable amounts depending on the conditions) on treating 2 with acid. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The reduction of [Mo2(Cp)2(µ-SMe)3(µ-O)]+ (1+) has been investigated by cyclic voltammetry and controlled-potential electrolysis in THF- and MeCN/NBu4PF6 without added acid or in the presence of various acids HX (HX: HTsO, CF3CO2H, HBF4). Reduction in the presence of acid follows an ECrevE mechanism in which the intermediate chemical step is an acid-base equilibrium between 1 and [Mo2(Cp)2(µ-SMe)3(µ-OH)]+ (2+). This electrochemical process is followed by protonation of the neutral µ-hydroxo complex 2 to afford different products which depend both on the solvent (THF or MeCN) and on the nature of the acid. Controlled-potential electrolysis of 1+ in the presence of HX (2 equiv.) leads to the generation of binding sites and finally gives products identical to those obtained from protonation of 2 by HX. The complex [Mo2(Cp)2(µ-SMe)3(µ-η1,η1-OCOCF3)] (3) which can be obtained either by protonation of 2 by CF3CO2H or by reduction of 1+ in the presence of CF3CO2H, has been characterized crystallographically. In the presence of HBF4 protonation of 1+ gives 22+. The reactivity of 2+ and of the complexes [Mo2(Cp)2(µ-SMe)3(H2O)(TsO)] (4) and [Mo2(cp)2(µ-SMe)3(H2O)L]+ (L = H2O or THF) (6+), all of which contain a terminal aqua ligand, has also been investigated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The paramagnetic μ-amidato species [Mo2Cp2(μ-MeCONH)(μ-SMe)3]BF42a+ (Cp = η-C5H5) is formed exclusively when the compound [Mo2Cp2(MeCN)2(μ-SMe)3]BF41a in powder form is kept in air, whereas the same starting complex in solution gives a mixture of the μ-amidato species and the μ-oxo complex [Mo2Cp2(μ-O)(μ-SMe)3]BF43. The oxo complex is formed quantitatively on warming [Mo2Cp2(μ-Cl)(μ-SMe)3]BF4 in water. The reduction of 2a+ by NaBH4 in CH3CN affords the molecular product [Mo2Cp2(μ-MeCONH)(μ-SMe)3] 2a which has been characterised by X-ray analysis.