Chloro complexes [RuCl(N-N)P-3]BPh4 (1-3) [N-N = 2,2'-bipyridine, bpy; 1,10-phenanthroline, phen; 5,5'-dimethyl-2,2'-bipyridine, 5,5'-Me(2)bpy; P = P(OEt)(3), PPh(OEt)(2) and PPh2OEt] were prepared by allowing the [RUCl4(N-N)]-H2O compounds to react with an excess of phosphite in ethanol. The bis(bipyridine) [RuCl(bPY)(2){P(OEt)(3)}]BPh4 (7) complex was also prepared by reacting RuCl2(bPY)(2).2H(2)O with phosphite and ethanol. Treatment of the chloro complexes 1-3 and 7 with NaBH4 yielded the hydride [RuH(N-N)P-3]BPh4 (4-6) and [RuH(bpy)(2)P]BPh4 (8) derivatives, which were characterized spectroscopically and by the X-ray crystal structure determination of [RuH(bpy){P(OEt)(3)}(3)]-BPh4 (4a). Protonation reaction of the new hydrides with Bronsted acid was studied and led to dicationic [Ru(eta(2)-H-2)(N-N)P-3](2+) (9, 10) and [Ru(eta(2)-H-2)(bpy)(2)P](2+) (11) clihydrogen derivatives. The presence of the eta(2)-H-2 ligand was indicated by a short T-1min value and by the measurements of the J(HD) in the [Ru](eta(2)-HD) isotopomers. From T-1min and J(HD) values the H-H distances of the dihydrogen complexes were also calculated. A series of ruthenium complexes, [RuL(N-N)P-3](BPh4)(2) and [RuL(bpy)(2)P](BPh4)(2) (P = P(OEt)(3); L = H2O, CO, 4-CH3C6H4NC, CH3CN, 4-CH3C6H4CN, PPh(OEt)(2)], was prepared by substituting the labile eta(2)-H-2 ligand in the 9, 10, 11 derivatives. The reactions of the new hydrides 4-6 and 8 with both mono- and bis(aryldiazonium) cations were studied and led to aryldiazene [Ru(C6H5N=NH)(N-N)P-3](BPh4)(2) (19, 21), [{Ru(N-N)P-3}(2)(mu-4,4'-NH=NC6H4-C6H4N=NH)](Bph(4))(4) (20), and [Ru(C6H5N=NH)(bpy)(2)P](BPh4)(2) (22) derivatives. Also the heteroallenes Co-2 and Cs-2 reacted with [RuH(bpy)(2)P]BPh4, yielding the formato [Ru{eta(1)-OC(H)=O}(bpy)(2)P]BPh4 and dithioformato [Ru{eta(1)-SC(H)=S}(bpy)(2)P]BPh4 derivatives.