Abstract: The synthesis of the non-classical ruthenium dihydrogen complexes [Ru(dtbpmp)H2(H2)] (PNP-pincer backbone) and [Ru(dtbpoet)(H2)H2] (POP-pincer backbone) with constrained geometries, their application in homogeneous catalysis and their reactivity towards small molecules like N2, CO2 and CO is described. The complexes with side-on bonded molecular hydrogen were analysed by NMR (T1-analysis), FT-IR and by means of DFT calculations. Ruthenium dihydrogen complexes have a great potential as catalysts for CH-activation, especially for H/Dexchange and hydrogen transfer processes. We successfully generated a ruthenium hydride catalyst for the H/D-exchange between (hetero)aromatic or olefinic protons and D2O (or C6D6)under mild conditions. The H/D-exchange processes included mechanistic investigation (NMR-kinetics and DFT calculations). Interestingly, it is also catalytically active in acceptorless dehydrogenation of alcohols to esters and some other reactions.