Reaction of (PNP)Os(H)(3) (PNP = ((Bu2PCH2SiMe2)-Bu-t)(2)N-) with N2O forms (PNP)OsH(N-2) and H2O in 1 h at 22 degrees C. The mechanism of this reaction is probed with DFT (B3LYP) calculations. (PNP)OsH(N-2) forms a 1:1 adduct with CO and with HCCH and is protonated (by triflic acid) to [PN(H)P]OsH(N-2)(+), which only slowly transforms to (PNP)Os(H)(2)(OTf) by liberation of N-2.