Influence of metal core composition on redox properties and photoreactivity of the clusters [H4-xRu4-xRhx(CO)(12)] (x=0, 2, 3, 4)

Electrochemical properties of tetrahedral clusters [H2Ru2Rh2(CO)(12)], [HRu Rh3(CO)(12)] and [Rh-4(CO)(12)] were investigated in order to evaluate the influence of metal core composition in the series [H4-xRu4-xRhx(CO)(12)] (x = 0-4). The cluster [H3Ru3Rh(CO)(12)] was not available in sufficient quan tities. As reported for [H4Ru4(CO)(12)], electrochemical reduction of the h ydride-containing clusters [H2Ru2Rh2(CO)(12)] and [HRuRh3(CO)(12)] also res ults in (stepwise) loss of hydrogen, producing the anions [HRu2Rh2(CO)(12)] (-), [Ru2Rh2(CO)(12)](2-) and [RuRh3(CO)(12)](-). These anions can also be prepared from the neutral parent clusters via chemical routes. Electrochemi cal reduction of [Rh-4(CO)(12)] does not result in the formation of any sta ble tetranuclear anion. Instead, [Rh-5(CO)(15)](-) and [Rh-6(CO)(15)](2-) a re the major reduction products detected in the course of IR spectroelectro chemical experiments. Most likely, these cluster species are formed from th e secondary CO-loss product [Rh-4(CO)(11)](2-) by fast redox condensation r eactions. Their reoxidation regenerates parent [Rh-4(CO)(12)], together wit h some [Rh-6(CO)(16)]. Unlike [H4Ru4(CO)(12)] that undergoes photochemical CO-dissociation, [H2Ru2Rh2(CO)(12)] and [Rh-4(CO)(12)] are completely photo stable in neat hexane and dichloromethane as well as in the presence of oct -1-ene.