Oxidation Chemistry of Inorganic Benzene Complexes

The oxidation of the 28 VE cyclo-E₆ triple-decker complexes [(Cp^R Mo)₂ (μ,η⁶ :η⁶ -E₆ )] (E=P, Cp^R =Cp(2 a), Cp*(2 b), Cp^Bn (2 c)=C₅ (CH₂ Ph)₅ ; E=As, Cp^R =Cp*(3)) by Cu⁺ or Ag⁺ leads to cationic 27 VE complexes that retain their general triple-decker geometry in the solid state. The obtained products have been characterized by cyclic voltammetry (CV), EPR, Evans NMR, multinuclear NMR spectroscopy, MS, and structural analysis by single-crystal X-ray diffraction. The cyclo-E₆ middle decks of the oxidized complexes are distorted to a quinoid (2 a) or bisallylic (2 b, 2 c, 3) geometry. DFT calculations of 2 a, 2 b, and 3 persistently result in the bisallylic distortion as the minimum geometry and show that the oxidation leads to a depopulation of the σ-system of the cyclo-E₆ ligands in 2 a-3. Among the starting complexes, 2 c is reported for the first time including its preparation and full characterization.