(α-Diimine)tricarbonylhalorhenium complexes: the oxidation side

Abstract

The electrochemical behaviour of the complexes [Re(CO)₃X(α-diimine)], X = Cl or Br, α-diimine = 1,4-di-tert-butyl-1,4-diaza-1,3-diene, was reinvestigated using cyclic voltammetry accompanied by IR and UV-vis spectroelectrochemistry. While the reduction results in the loss of halide, as necessary for the electrocatalytic activity of related diimine compounds, a reversible oxidation could be observed for the chloro complex 1 (X = Cl). The conversion of 1 to 1⁺ in CH₂Cl₂ or CH₃CN is accompanied by high-frequency shifts (Δν = 73–114 cm⁻¹) of the three carbonyl stretching bands, by a considerable change in carbonyl stretching modes, and by changed absorption in the visible region. DFT calculations support the spectroelectrochemical results and suggest an unusually large g anisotropy (g₁ 1.38, g₂ 2.06, g₃ 3.20) which explains the absence of detectable EPR signals for 1⁺ under normal X band conditions. Frontier orbitals calculated by DFT for 1 reveal two close lying occupied orbitals (HOMO, HOMO-1) with Re–Cl character and a diimine based LUMO.