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

The Fe III azide complexes [Fe III (N 3 )cyclam‐ac]PF 6 ( 1 ⋅PF 6 ), [Fe III (N 3 )Me 3 cyclam‐ac]PF 6 ( 2 ⋅PF 6 ), and trans ‐[Fe III (N 3 ) 2 cyclam]ClO 4 ( 3 ⋅ClO 4 ) (cyclam=1,4,8,11‐tetraazacyclotetradecane; cyclam‐ac=1,4,8,11‐tetraazacyclotetradecane‐1‐acetate; Me 3 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 2 to form a high‐valent Fe V 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 II . 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 3 without change in the iron oxidation state. However, small amounts of dinitrogen loss and thus Fe V nitride formation are also observed. While it is assumed that the Fe V 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 V (N)(N 3 )(cyclam)] + still bearing an intact second azide and the coordinatively unsaturated [Fe V (N)(cyclam‐H)] + are observed in the gas phase.