Reactivity of nitrido-carbonyl clusters:: synthesis and solid state structure of [Fe5MnN(CO)16]2- and [Fe6N(CO)14NO]2-;: oxidation of a cluster-coordinated nitride

The cluster [Fe5MnN(CO)(16)](2-) (1) was synthesized from [Fe6N(CO)(15)](3-) and Mn-2(CO)(10), in refluxing EtCN, or [Fe4N(CO)(12)](-) and [FeMn(CO)(9)](-). Its solid state structure was determined on the [Me3NCH2Ph](+) salt, and consists of an octahedral metal cage, enclosing a six-coordinated nitrido ligand. The position of the manganese atom in the solid state could be established, despite some crystallographic disorder, by considering the local stereochemistry of the ligands. The cluster [Fe6N(CO)(14)NO](2-) (2) was obtained in moderate yields by the reaction of [Fe4N(CO12](-) with Mo(CO)(3)(EtCN)(3). The nitrosyl is formed by oxidation of the starting nitride, and the source of the oxygen is presumably a carbonyl, whose splitting is mediated by the molybdenum complex. This process is the first example of an oxidation of a nitride in a carbonyl cluster. The solid state structure of the iron cluster is also octahedral, and the linear nitrosyl ligand was unambiguously located from the short Fe-N bond distance, and from dishomogeneous distribution of ligands. Cyclic voltammetric studies have shown that electron transfer processes are followed by chemical reactions thus testifying that no stable redox congeners exist for these two nitride clusters.