The combination of variable temperature (190-297 K) IR and NMR spectroscopy studies with quantum-chemical calculations at the DFT/B3PW91 and AIM level had the aim to determine the mechanism of proton transfer to CpRuH(dppe) (1, dppe = Ph2P(CH2)(2)PPh2) and the structures of intermediates. Dihydrogen bond (DHB) formation was established in the case of interaction with weak proton donors like CF3CH2OH. Low-temperature protonation (at about 200 K) by stronger proton donors leads via DHB complex to the cationic nonclassical complex [CpRu(eta(2)-H-2)(dppe)](+) (2). Thermodynamic parameters of DHB formation (for CF3CH2OH: Delta H degrees(HB) = -4.9 +/- 0.2 kcal.mol(-1), Delta S degrees(HB) = -17.8 +/- 0.7 cal.mol(-1).K-1) and proton transfer (for (CF3)(2)CHOH: Delta H degrees(PT) = -5.2 +/- 0.3 kcal.mol(-1), Delta S degrees(PT) = -23 +/- 1 cal.mol(-1).K-1) were determined. Above 240 K 2 transforms into trans-[CpRu(H)(2)(dppe)](+) (3) yielding a mixture of 2 and 3 in 1:2 ratio. Kinetic analysis and activation parameters for the "[Ru(eta(2)-H2)](+) -> trans-[Ru(H)(2)](+n)" transformation indicate reversibility of this process in contrast to irreversible intramolecular isomerization of the Cp* analogue. Calculations show that the driving force of this process is greater stability (by 1.5 kcal.mol(-1) in Delta E scale) of the dihydride cation in comparison with the dihydrogen complex. The calculations of the potential energy profile indicate the low barrier for deprotonation of 2 suggesting that the formation of trans-[CpRu(H)(2)(dppe)](+) proceeds via deprotonation of [Ru(eta(2)-H-2)](+) to DHB complex, formation of hydrogen bond with Ru atom and subsequent proton transfer to the metal site.