The protonation with Bronsted acids HB (HBF4 and CF3CO2H) of [RuH2(arene)(PPh2Het)] derivatives (PPh2Het = dpim, Het = 2-N-methylimidazolyl; PPh2Het = PPh2py, Het = 2-pyridyl) that contain uncoordinated N atoms has been analyzed experimentally by NMR spectroscopy and through computational studies. Initially, at low temperature, the uncoordinated N atoms of the phosphine are protonated and a proton–hydride exchange is observed by 1H NMR spectroscopy. The proton transfer leads to the corresponding cationic trihydride intermediates, which exhibit a dual character of classical and nonclassical hydrides, with the nonclassical species being more stable, especially when Het = 2-pyridyl. In fact, the release of H2 and the formation of the respective monohydride complexes [RuH(arene)(κ2-N,P-PPh2Het)]B was observed at room temperature. The participation of the uncoordinated N center in the proton transfer process in the stabilization of RuH(H2)+ with respect to RuH3+ species and in the hydride–dihydrogen exchange (...