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.