The ruthenium cluster Ru3(CO)12 (1) has been evaluated as a catalyst precursor for the thermal reactions of 1-octene with (EtO)3SiH in a mixture of dioxane and benzene at temperatures of 50–75°C. At 70°C or higher, olefin isomerization and hydrosilylation reactions were observed; the products, trans-2-octene and C5H11CH2CH2CH2Si(OEt)3 (2) were identified. The reactions were accompanied by a side reaction that involved generation of hydrogen gas. The sum of the rates of appearance of 2 and H2 equalled the rate of disappearance of (EtO)3SiH. No significant isomerization was observed in the absence of (EtO)3SiH. Maximum turnover number values of 750, 70, and 70 were obtained for isomerization, hydrosilylation, and H2 production reactions, respectively. At 60°C or lower, no hydrosilylation or hydrogen production was observed, and the only product was trans-2-octene. No detectable disappearance of (EtO)3SiH was observed. Acetophenone was also hydrosilated by use of cluster 1, as catalyst; the only product obtained was (EtO)3SiOC(Ph)(H)(CH3). Kinetic studies indicated that the reactions of 1-octene and the reaction of acetophenone involved a catalytically active species of lower nuclearity. There was evidence of concurrent cluster catalysis, especially during the first few minutes of the reaction.