The bulky diphosphine 1,2-bis(diisopropylphosphino)ethane (dippe) reacts with [RuCl2(PPh3)3] to yield [RuCl2-(dippe)2] (1), from which the complex cis-[RuH2(dippe)2] (2) can be prepared by reaction with Na[BH4]. The hydrido-chloride complex [RuHCl(dippe)2](3) is obtained by displacement of triphenylphosphine ligands in [RuHCl-(PPh3)3] by dippe. Complex 3 dissociates one chloride ligand in methanolic or ethanolic solutions generating the 16-electron, five-coordinate species [RuH(dippe)2]+, which can be isolated as the tetraphenylborate salt (4). This compound does not react with dinitrogen or ethylene, but it reacts with CO,CNBu(t), or nitriles yielding the corresponding 18-electron trans-octahedral derivatives [RuH(L)(dippe)2][BPh4] (L = CO (5), CNBu(t) (6), PhCN (7), or MeCN (8)). 2 also reacts with dihydrogen yielding [RuH(H2)(dippe)2][BPh4] (9), which is only stable under a dihydrogen atmosphere. Both 2 and 9 react with dioxygen to form the hydridodioxygen complex [RuH(eta2-O2)(dippe)2][BPh4] (10), which is a rare example of dioxygen coordination at a dihydrogen-binding site. The crystal structure of 10 has been determined. Crystal data : Monoclinic system, space group P2(1)/n, a = 16.698(2) angstrom, b = 15.498(2) angstrom, c = 20.635(4) angstrom, beta = 103.40(1)-degrees, and Z = 4. It represents the first structural report of a hydrido-dioxygen complex. Behavior analogies of ruthenium-dippe and ruthenium-dcpe(dcpe = 1,2-bis(dicyclohexylphosphino)ethane)complexes are also discussed.