Electrochemical Studies of Complexes with Oxo‐ or Hydroxo‐Bridged {Mo 2 (µ‐SMe) 3 } + Centers: Cleavage of the Oxygen Bridge and Generation of Substrate‐Binding Sites

The reduction of [Mo 2 (Cp) 2 (µ‐SMe) 3 (µ‐O)] + ( 1 + ) has been investigated by cyclic voltammetry and controlled‐potential electrolysis in THF‐ and MeCN/NBu 4 PF 6 without added acid or in the presence of various acids HX (HX: HTsO, CF 3 CO 2 H, HBF 4 ). Reduction in the presence of acid follows an EC rev E mechanism in which the intermediate chemical step is an acid‐base equilibrium between 1 and [Mo 2 (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 [Mo 2 (Cp) 2 (µ‐SMe) 3 (µ‐η 1 ,η 1 ‐OCOCF 3 )] ( 3 ) which can be obtained either by protonation of 2 by CF 3 CO 2 H or by reduction of 1 + in the presence of CF 3 CO 2 H, has been characterized crystallographically. In the presence of HBF 4 protonation of 1 + gives 2 2+ . The reactivity of 2 + and of the complexes [Mo 2 (Cp) 2 (µ‐SMe) 3 (H 2 O)(TsO)] ( 4 ) and [Mo 2 (cp) 2 (µ‐SMe) 3 (H 2 O)L] + (L = H 2 O 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)