The novel trans-[Ru(II)Cl2(H2C=C(CH2PPh2)2)(diamine)]1-3complexes {diamine is1,2-ethanediamine1,1,3-propanediamine2and2,2-dimethyl-1,3-propanediamine3}were obtained by reacting trans-[RuCl2[H2C=C(CH2PPh2)2]2 with an excess amount of corresponding diaminein CH2Cl2as solvent. One of the diphosphine ligands was quantitatively replaced by the corresponding diamine, even when excess diamine was added. In solution only the trans-[RuCl2(H2C=C(CH2PPh2)2)(diamine)] isomer configuration was confirmed by NMR spectroscopyand theX-ray crystal structure of 2.These diphosphine complexes have exhibited significant activity and selectivity as hydrogenation catalystsfor a,ß-unsaturated ketone.The catalytic activity were compared to an analogous trans–[Ru(II)Cl2(H2C(CH2PPh2)2)(diamine)]4-6 {diamine is 1,2-ethanediamine 4 ,1,3-propanediamine5and2,2-dimethyl-1,3-propanediamine6}.Complexes 1-3 werecatalyzeda,ß-unsaturated ketone faster than the previously reported complexes 4-6. Density functional theory (DFT) calculationshave been carried out to study the shift in the Ru(III)/Ru(II) couple and the catalytic activity for the two representative complexes 2 and 5.