Three complexes of the general formula trans/cis-[Ru(II)(dppme)(N–N)Cl2] {dppme is H2C=C(CH2PPh2)2 and N–N is 1,2-diaminocyclohexane (trans/cis-(1)) and 1-methyl-1,2-diaminopropane (trans-(2)} were obtained by reacting trans-[RuCl2(dppme)2] with an excess amount of corresponding diamine in CH2Cl2 as a solvent. The complexes were characterized by an elemental analysis, IR, 1H, 13C and 31P{1H}NMR, FAB-MS and Uv-visible. The trans-(1) (kinetic product) readily isomerizes to the cis-(1) (thermodynamic product) and this process was followed by using 31P{1H} NMR, cyclic voltammetry and UV–vis. The electrochemical studies on complex (1) reveal that the Ru(III)/Ru(II) couples are sensitive to the isomer (trans/cis) formed. The structureof cis-(1) isomer was confirmed by X-ray analysis and 31P{1H} NMR. Transfer-hydrogenation reactions for reduction of trans-4-phenyl-3-butene-2-one were conducted using complexes trans/cis-(1) and trans-(2). The electronic spectra of cis/trans-(1) in dichloromethane were calculated with the use of time-dependent DFT methods.