The reaction of Na[RuCp(CO)(2)] with [MnCp'(CO)(2)(NO)]BF4 gives the corresponding heterometallic derivative [MnRuCpCp'(mu-CO)(2)(CO)(NO)] (Cp = eta(5)-C5H5; Cp' = eta(5)-C5H4Me). In contrast, the group 6 metal carbonyl anions [MCP(CO)(2)L](-) (M = Mo, W; L = CO, P(OMe)(3), PPh3) react with the Mn and Re complexes [M'CP'(CO)(2)(NO)]BF4 to give the heterometallic derivatives [MM'CpCp'(mu-N)(CO)(3)L) having a nitride ligand linearly bridging the metal centers (W-N = 1.81(3) angstrom, N-Re = 1.97(3) angstrom, W-N-Re = 179(1)degrees, in [WReCpCp'(mu-N)(CO)(3){P(OMe)(3)}])Density-functional theory calculations on the reactions of [WCp(CO)(3)](-) and [RuCP(CO)(2)](-) with [MnCp(CO)(2)(NO)](+) revealed a comparable qualitative behavior. Thus, two similar and thermodynamically allowed reaction pathways were found in each case, one implying the displacement of CO from the cation and formation of a metal-metal bond, the other implying the cleavage of the N-O bond of the nitrosyl ligand and release of a carbonyl from the anion as CO2. The second pathway is more exoergonic and is initiated through an orbitally controlled attack of the anion on the N atom of the NO ligand in the cation. In contrast, the first pathway is initiated through a charge-controlled attack of the anion to the C atom of a CO ligand in the cation. The CO2-elimination pathway requires at the intermediate stages a close approach of the NO and CO ligands, which is more difficult for the Ru compound because of its lower coordination number (compared to W). This effect, when combined with a stronger stabilization of the initial intermediate in the Ru reaction, makes the CO2-elimination pathway slower in that case.