The systems Ru3(CO)12·nL, (L = PPh3, CH3CN, (EtO)3Si(CH2)3NH2; n = 0–3, 15) have been employed as catalysts and/or catalyst precursors for thermal hydrogenation and isomerization reactions of 1-octene under moderate reaction conditions (1 atm at 70°C or below). In the hydrogenation reaction the system Ru3(CO)12/15CH3CN showed the highest activity, with turnover numbers up to 1000. For this system the kinetics indicated that the hydrogenation occurs via a lower nuclearity catalytic species formed by fragmentation of the mother cluster. On the other hand the isomerization reaction occurs, after a 10–20 min induction period, by higher-nuclearity catalytic species. The isomerization gave trans-2-octene only, and none of the cis-isomer. The effects of other factors on the rates of hydrogenation and isomerization reactions are described.