Iron Azides with Cyclam-Derived Ligands: Are They Precursors for High-Valent Iron Nitrides in the Gas Phase?

The Fe azide complexes [Fe (N )cyclam-ac]PF (1⋅PF ), [Fe (N )Me cyclam-ac]PF (2⋅PF ), and trans-[Fe (N ) cyclam]ClO (3⋅ClO ) (cyclam=1,4,8,11-tetraazacyclotetradecane; cyclam-ac=1,4,8,11-tetraazacyclotetradecane-1-acetate; Me cyclam-ac=4,8,11-trimethyl-1,4,8,11-tetraazacyclotetra-decane-1-acetate) are studied in the gas phase with special emphasis on the formation of high-valent iron nitrides by collision-induced dissociation. Whereas the azide complex with unsubstituted cyclam-acetate 1 as major fragmentation expels N to form a high-valent Fe nitride complex, a similar process is not observed for its methyl-substituted congener. In contrast, loss of an azide radical results in iron reduction to Fe . Thus, the gas-phase behavior is parallel to the results obtained in spectroscopic studies of photolyzed frozen solution. The diazide complex 3 mainly fragments via consecutive losses of HN without change in the iron oxidation state. However, small amounts of dinitrogen loss and thus Fe nitride formation are also observed. While it is assumed that the Fe nitride complex detected by Mössbauer spectroscopy in frozen solution is still coordinated by an azide in the trans position to the nitride, both the complex [Fe (N)(N )(cyclam)] still bearing an intact second azide and the coordinatively unsaturated [Fe (N)(cyclam-H)] are observed in the gas phase.