Redox properties of the 17-electron sandwich (eta(5)-C5H5)Mo(eta(6)-C6Ph6): electrochemical characterization of the 16e(-) Lewis acid monocation and its PF6- adduct

Thermolysis of CpMo(CH2C6H5)(eta(2)-PhC2Ph)[P(OMe)(3)] [Cp = (eta(5)-C5H5)] unexpectedly gives the mixed-sandwich 17-electron metallocene CpMo(eta(6)- C6Ph6), 1. The title compound undergoes reversible one-electron oxidation ( E-1/2 = - 0.25 V vs. ferrocene) and reduction (E-1/2 = - 2.02 V) reactions which were characterized by voltammetry and coulometry. When the oxidation of 1 is accomplished in CH2Cl2/[Bu4N][PF6] electrolyte, the 16 e(-) Mo(II) complex 1(+) is in equilibrium with a thermodynamically-favored product for mulated as the [PF6](-) adduct, 1-FPF5, 3. Adduct 3 remains intact upon fur ther one-electron oxidation to the Mo(III) complex 3(+), but it rapidly rel eases [PF6](-) when reduced to the Mo(I) species 3(-). Other counterions su ch as [BF4](-) and [ClO4](-) do not show the same degree of interaction wit h the 16 e(-) Mo(II) cation. (C) 1999 Elsevier Science S.A. All rights rese rved.