Oxidatively-induced μ-η 1 → μ-η 1 :η 1 rearrangement of {NN} ligands at a {Mo 2 (μ-SMe) 3 } site and protonation of the oxidized diazenido complex

Abstract : The electrochemical oxidation of [Mo2(cp)2(μ-SMe)3(μ-N2Ph)] and [Mo2(cp)2(μ-SMe)3(μ-N2HPh)]+ complexes where the diazo bridge adopts either an η1 or an η1:η1 coordination mode has been studied by cyclic voltammetry and controlled-potential electrolysis in THF– and CH2Cl2–[NBu4][PF6]. The electrochemical oxidation of [Mo2(cp)2(μ-SMe)3(μ-η1-N2Ph)] 1 and of [Mo2(cp)2(μ-SMe)3(μ-η1-N2HPh)]+1-H+++ triggers the isomerization of the diazo bridge to the η1:η1 mode found in 2+++ and 2-H2+2+2+ respectively. The electrochemical oxidation of [Mo2(cp)2(μ-SMe)3(μ-η1:η1-N2Ph)] 3 and of [Mo2(cp)2(μ-SMe)3(μ-η1:η1-HN2Ph)]+3-H+++ with a syn (“up–up”) arrangement of the Me substituents of the equatorial sulfur bridges is also followed by an isomerization to 2+++ and 2-H2+2+2+, respectively, with an anti (“up–down”) configuration of the equatorial Me groups. The rates of the isomerization 1++ → 2+++, 1-H2+2+2+ → 2-H2+2+2+, and 3-H2+2+ → 2-H2+2+2+ were studied by cyclic voltammetry at different scan rates and at different temperatures. The isomerization of the protonated complexes with either a hydrazido(2−) or a diazene bridge (respectively 1-H2+2+2+ and 3-H2+2+) is faster than that of the diazenido precursors (respectively 1++ and 3++). The diazenido complex 2+++ protonates readily, affording 2-H2+2+2+, while 2-H3+3+ undergoes proton loss.