The reactions of several mono- and poly-nuclear carbonyl metallates with nitrosonium ion have been studied. Besides simple substitution of a carbon monoxide with NO+ some reactions yielded products containing other nitrogeneous ligands. When [CoRu3(CO)13]- reacts with NO+, low yields of the new nitrido cluster CoRu3N(CO)12 are formed. Prior conversion of [CoRu3(CO)13]- to the new hydrido cluster [H2CoRu3(CO)12]- under hydrogen, followed by nitrosylation, forms the new imido cluster H2Ru3(NH)(CO)9 in very low yield. The reaction of [FeCO3(CO)12]- with NO+ also generates an imido cluster, FeCo2(NH)(CO)9, in 15% yield. This cluster has been characterized by X-ray crystallography and was found to be similar to the tricobalt alkylidyne clusters. (Triclinic crystal system, P1 space group, Z=2, a 6.787(1), b 8.016(1), c 13.881(2) Å, α 95.50(1), β 100.77(1), γ 107.93(1)°. Modifications of the nitrosylations using NO+ were studied. In particular, the addition of triethylamine or N-t-butylbenzaldimine allowed the use of NO+ in THF without solvent decomposition. With [CpMo(CO)3]- and [CpFe(CO)2]- the N-nitrosoiminium species appears to form transient alkylmetals which further react to give the dimers [CpMo(CO)3]2 and [CpFe(CO)2]2.