The complex [{HB(pz) 3 }RuCl(PPh 3 ) 2 ] reacts with one equivalent of dippe in toluene to yield [{HB(pz) 3 }RuCl(dippe)]. This compound reacts with NaBH 4 in MeOH furnishing the monohydride [{HB(pz) 3 }RuH(dippe)], whereas [{HB(pz) 3 }RuH(PPh 3 ) 2 ] was obtained by reaction of [RuHCl(PPh 3 ) 3 ] with K[HB(pz) 3 ]. Both monohydride complexes are protonated by HBF 4 OEt 2 at -80°C to give the corresponding dihydrogen adducts [{HB(pz) 3 }Ru(H 2 )(dippe)] + and [{HB(pz) 3 }Ru(H 2 )(PPh 3 ) 2 ] + , as inferred from longitudinal relaxation time (T 1 ) and 1 J(H,D) measurements. The latter complex is unstable and decomposes at room temperature, but the former is a stable species which does not rearrange to the dihydride form when the temperature is raised. The X-ray crystal structure of [{HB(pz) 3 }Ru(H 2 )(dippe)][BPh 4 ] has been determined. The dihydrogen ligand in this compound is labile, and readily replaced by a range of neutral donor molecules, yielding the corresponding complexes [{HB(pz) 3 }Ru(L)(dippe)](BPh 4 ] (L = CO, CNBu t , Me 2 CO, thf, N 2 ). There is also supporting evidence for the formation of a paramagnetic Ru I I I methoxide complex, namely [{HB(pz) 3 }Ru(OMe)(dippe)][BPh 4 ]. All compounds were characterized by IR, NMR and microanalysis.