Abstract The compounds with general formula RuCl 2 (L-L) 2 (L-L bidentate phosphine, Ph 2 P(CH 2 ) n PPh 2 , n = 4, 5, 6) catalytically hydrogenate unsaturated organic substrates such as olefins, dienes, aldehydes and ketones under moderate reaction conditions in polar solvents, even in the absence of NH 4 + salts. In general the catalytic activity follows the order n = 4 > n = 6 > n = 5. Small percentages of isomerization products of the terminal olefin are observed, which increase with the value of n . With 1,5-cyclooctadiene, the hydrogenation to the monoene is faster than the second hydrogenation, and follows the order n = 4 > n = 5 > n = 6.