High nuclearity ruthenium carbonyl cluster chemistry VI¹. Cyclic voltammetric and spectroelectrochemical studies of [Ru₁₀(μ-H)(μ₆-C)(CO)₂₄]^- and [Ru₁₀(μ₆-C)(CO)₂₄]^2-

The reductive electrochemistry of the decaruthenium clusters [Ru₁₀(μ-H)(μ₆-C)(CO)₂₄]^- (1) and [Ru₁₀(μ₆-C)(CO)₂₄]^2- (2) has been examined by cyclic voltammetry and UV-Vis spectroelectrochemistry, the latter using an optically transparent thin-layer electrode (OTTLE) cell. Two-electron reduction of both 1 and 2 proceeds in an electrochemically non-reversible fashion to give ^#[HRu₁₀(μ₆-C) (CO)₂₄]^3- and ^#[Ru₁₀(μ₆-C) (CO)₂₄]^4-, respectively, with an associated structural change (indicated ^#) which is proposed to involve apical Ru-Ru bond cleavage. Two-electron oxidation of these electrochemically-generated species at low temperature proceeds in a reversible fashion to afford ^#[HRu₁₀(μ₆-C) (CO)₂₄]^- and ^#[Ru₁₀(μ₆-C) (CO)₂₄]^2-, respectively, with no further gross structural change, whereas two-electron oxidation at room temperature proceeds by way of apical Ru-Ru bond reformation to regenerate 1 and 2. The effect of the hydride ligand in the decaruthenium clusters is to favor reduction and disfavor oxidation by ∼0.3 V. Results with these clusters contrast with the reported behavior of stepwise reductions observed for isostructural [Os₁₀(μ₆-C) (CO)₂₄]^2-, where no structural adjustment was observed to accompany the first one-electron reduction, and only a minor change (cluster vertex expansion) accompanied the second one-electron reduction, differences between these systems being assigned to varying M-M bond strengths.