Water soluble RuCl2(DMSO)(4) is an active catalyst precursor for 1-hexene hydrogenation in water/organic solvent biphasic systems, reaching 98% total conversion (400 psi H-2, 80(degrees)C, 6 h), with n-hexane as the principal product and less of the 2-hexene isomers, favoring cis-2-hexene. It is very sensitive to O-2 dissolved in water, and decomposes when halide salts or alcohols are added. The Ru complex is also active in an alcohol homogeneous phase, but less than in the biphasic system, gives a greater isomer proportion, favoring cis-2-hexene and increases with potassium halide salt additives.