Oxidatively-induced μ-η1 → μ-η1:η1 rearrangement of {NN} ligands at a {Mo2(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.