Electrochemical Studies of Complexes with Oxo‐ or Hydroxo‐Bridged {Mo₂(µ‐SMe)₃}⁺ Centers: Cleavage of the Oxygen Bridge and Generation of Substrate‐Binding Sites

Abstract

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)

Transformations and Agostic Interactions of Hydrocarbyl Ligands Bonded to the Sulfur-Rich Dimolybdenum Site {Mo2Cp2(μ-SMe)3}: Chemical and Electrochemical Formation of μ-Alkyl and μ-Vinyl Compounds from a μ-Alkylidene Derivative

“…The increase in the amount of the μ-chloro complex is tentatively assigned to reactions of 2 and 3 with protons leading to the release of the hydrocarbyl ligands and binding of a chlorine atom from the solvent. In agreement with this, controlled-potential electrolysis of 1 in the presence of 2 equiv of CF 3 CO 2 H produces 3 (75%) and the known trifluoroacetato-bridged complex [Mo 2 Cp 2 (μ-SMe) 3 (μ-η 1 :η 1 -OCOCF 3 )] (25%), characterized by its first oxidation at E 1/2 ox1 = −0.35 V, after the passage of ca. 1.9 F mol -1 of 1 .…”

Reactivity of Cyclopentadienyl Molybdenum Compounds towards Formic Acid: Structural Characterization of CpMo(PMe3)(CO)2H, CpMo(PMe3)2(CO)H, [CpMo(μ-O)(μ-O2CH)]2, and [Cp*Mo(μ-O)(μ-O2CH)]2

“…While dinuclear molybdenum compounds with bridging formate ligands are well-known, there are no examples listed in the Cambridge Structural Database (CSD) that also feature cyclopentadienyl ligands. Nevertheless, there are several examples of dinuclear cyclopentadienyl molybdenum compounds that incorporate other carboxylate ligands, as illustrated in Table . − …”

Activation of propargylic alcohols by dimolybdenum tris(μ-thiolate) complexes: Influence of the substituents R in HCCCR2(OH)-vinylidene/allenylidene transformation. Reactivity of allenylidene complexes

“…In fine, 16a was separated from the other complexes by crystallisation in cold dichloromethane-hexane. Compounds 17 [2d] and [Mo 2 Cp 2 (O)(Cl)(l-SMe) 3 ] [26] were identified by comparison of their 1 H NMR spectra with those of authentic samples. …”

“…Products 12, 16a, 16b and 17 were characterised analytically and from multinuclear ( 1 H and 13 C) NMR spectroscopic data given in Section 3. Complex 17 and the oxochloro by-product obtained in reaction (ij) (Scheme 6) were identified by comparing their 1 H NMR spectra with [26]. The presence of the alkynyl ligand in 12 was established from the 13 C-{ 1 H} spectrum which has only one resonance corresponding to the acetylenic carbon atoms [18a,2d] at 113.45 ppm and a singlet at 49.0 ppm due to the CPh 2 H. The close similarity of the 1 H NMR of 12 with those of 16a and 16b suggests that these three compounds have similar geometries and that 16a and 16b also contain alkynyl fragments.…”