Five new monocationic dihydrogen complexes of ruthenium of the type trans-[RuCl (eta(2)-H-2)(PP)(2)][BF4] (PP = bis-1,2(diarylphosphino)ethane, aryl = p-fluorobenzyl, 1a, benzyl, 2a, m-methylbenzyl, 3a, p-methylbenzyl, 4a, p-isopropylbenzyl, 5a) have been prepared by protonating the precursor hydricle complexes trans-[RuCl(H)(PP)(2)] using HBF4 center dot OEt2. The dihydrogen complexes are quite stable and have been isolated in the solid state. The intact nature of the H-H bond in these derivatives has been established from the short spin-lattice relaxation times (T-1, ms) and observation of substantial H, D couplings in the HD isotoporners. The H-H bond distances (d(HH), angstrom) increase systematically from 0.97 to 1.03 A as the electron-donor ability of the substituent on the diphosphine ligand increases from the p-fluorobenzyl to the p-isopropylbenzyl moiety. The d(HH) in trans-[Ru(eta(2)-H-2)(Cl)((C6H5-CH2)(2)PCH2CH2P(CH2C6H5)(2))(2)][BF4], 2a, was found to be 1.08(5) angstrom by X-ray crystallography. In addition, two new 16-electron dicationic dihydrogen complexes of the type [Ru (eta(2)-H-2)(PP)(2)][OTf](2) (PP = (ArCH2)(2)PCH2CH2P(CH2-Ar)(2), Ar = m-CH3C6H4-, 6a, p-CH3C6H4-, 7a) have also been prepared and characterized. These derivatives were found to possess elongated dihydrogen ligands.