A study of the protonation of three tetranuclear nitrido clusters having the butterfly geometry is reported. While the final product of each of these reactions is a hydrido-nitrido cluster, the intermediates contain the imido (NH) ligand which can be trapped by CO. For [FeRu3N(CO)12]1-, the products of protonation in a CO atmosphere are FeRu2(NH)(CO)10, [FeRu4N(CO)14]1-, and small amounts of HFeRu3N(CO)12and Ru3(CO)12. With [Ru4N(CO)12]1-, this reaction generates Ru3(NH)(CO)10, [Ru5N(co)14]1-, Hru4N(CO)12, and small quantities of Ru3(CO)12. The new NH-containing clusters FeRu2(NH)(CO)10and Ru3(Nh)(Co)10contain a triply bridging N–H ligand and a triply bridging carbon monoxide. The substituted cluster (FeRu3N(CO)10[P(OCH3)3]2|1-was shown by X-ray crystallography [crystal system = orthorhombic, space group = Pnn2, a = 11.603 (3) A, b = 18.521 (6) A, c = 8.908 (4) A, Z = 2] to contain the two Ru(CO)2[P(OCH3)3] fragments in the wing-tip positions. Protonation leads to a green intermediate that reacts with CO to give FeRu2(NH)(CO)9[P(OCH3)3], which was structurally characterized [crystal system = monoclinic, space group = P21/m, a = 8.596 (2) Å, β = 15.576 (3) A, c = 7.870 (4) A, (3 = 100.37 (3)°, Z = 2]. The structure contains both a triply bridging CO and NH ligand, and the phosphite is bound to a ruthenium and oriented trans to the NH group. 1H and 15N NMR spectroscopies were used to identify the intermediate imido cluster FeRu3(NH)(CO)10[P(OCH3)3]2.