High nuclearity ruthenium carbonyl cluster chemistry .6. Cyclic voltammetric and spectroelectrochemical studies of [Ru-10(mu-H)(mu(6)-C)(CO)(24)](-) and [RU10(mu(6)-C)(CO)(24)](2-)

The reductive electrochemistry of the decaruthenium clusters [Ru-10(mu-H)(mu(6)-C)(CO)(24)](-) (1) and [Ru-10(mu(6)-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(mu 6-C) (CO)(24)](3-) and (#)[Ru-10(mu(6)-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(mu g-C)(CO)(24)](-) and (#)[Ru-10(mu(6)-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 similar to 0.3 V. Results with these clusters contrast with the reported behavior of stepwise reductions observed for isostructural [Oslo(mu(6)-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.