Both Ru-3(CO)(12) and Ru-3(CO)(9)(PPh3)(3) were tested in their ability to hydrogenate and isomerize I-hexene at 30, 60 and 90 degreesC in the presence and absence of H-2. The effect of excess PPh3 was studied and interpreted by the different capacity of the duster to replace CO by PPh3 against CO. Some reactions under irradiation with visible light were also performed. The cluster mixtures obtained in hydrogenation reactions were characterized by TR spectroscopy and shown to contain H4Ru4(CO)(12) and H4Ru4(CO)(12-n)(PPh3)(n)(n = 1-4). Main isomerization products were trans 2-hexene(up to 61%), cis-2-hexene (up to 23%) and trans-3-hexene (up to 20%). At H-2-pressures of 32 and 48 psi, Ru-3(CO)(12) was more active in hydrogenation, at 16 psi Ru-3(CO)(9)(PPh3)(3) was the better hydrogenation catalyst. 2-Methyl-1-pentene (up to 48) and 2-methylpentane (up to 0.55%) were identified as by-products.