The protonation of [Ru-2(CO)(4)(mu-H)(mu-PBu2t)(mu-dppm)(mu-eta(2)-ONNO)] (1) with HBF4 occurs at the oxygen of the noncoordinating side of the trans-hyponitrite ligand to give [Ru-2(CO)(4)(mu-H)(mu-PBu2t)(mu-dppm)(mu-eta(2)-ONNOH)][BF4] (2) in good yield. The monoprotonated hyponitrite in 2 is deprotonated easily by strong bases to regenerate 1. Furthermore, 1 reacts with the methylating reagent [Me3O][BF4] to afford [Ru-2(CO)(4)(mu-H)(mu-PBu2t)(mu-dppm)(mu-eta(2)-ONNOMe)][BF4] (3). The molecular structures of 2 and 3 have been determined crystallographically, and the structure of 2 is discussed with the results of the DFT/B3LYP calculations on the model complex [Ru-2(CO)(4)(mu-H)(mu-PH2)(mu-H2PCH2PH2) (mu-eta(2)-ONNOH)](+) (2a). Moreover, the thermolysis of 2 in ethanol affords [Ru-2(CO)(4)(mu-H)(mu-OH)(mu-PBu2t)(mu-dppm)][BF4] (4) in high yield, and the deprotonation of 4 by DBU in THF yields the novel complex [Ru-2(CO)(4)(mu-OH)(mu-PBu2t)(mu-dppm)] (5).