The ruthenium(IV) nitride complex (PNP)RuN (PNP = ((Bu2PCH2)-Bu-t-SiMe2)(2)N-) reacts rapidly with 2NO to form (PNP)Ru(NO) and N2O, via no detectable intermediate. The linear nitrosyl complex has a planar structure. In a slower reaction, (PNP)RuN reacts with N2O by O-atom transfer (established by N-15 labeling) to give the same nitrosyl complex and N-2. Density functional theory (B3LYP) calculations show both reactions to be very thermodynamically favorable. Analysis of possible intermediates in each reaction shows that radical (PNP)RuN(NO) has much spin density on nitride N (hence, N2-), while one 2 + 3 metallacycle, (PNP)RuN3O, has the wrong connectivity to form a product. Instead, an intermediate with a doubly bent N2O (hence, a two-electron reduced N-nitrosoimide form) brings the O atom in proximity to the nitride N on the path to a product.