Nitrosation of a dimetal bridge sulfur was observed for reactions of dimolybdenum(V) anions of the general form [Mo-2(NAr)(2)(S2P(OEt)(2))(2)(mu-S)(2)(mu-O(2)CR)](-) with ClNO ((ClNO)-N-15), NO+, NO2- ((NO2-)-N-15), or i-C5H11ONO The products were thionitrites containing the SNO- bridge ligand. The compounds were very reactive and underwent rapid nitrosyl migration reactions even at low temperatures. The migration resulted in overall oxo-for-imido exchange. after which additional processes ensued.