Second known Fe(VI) complex debuts

Chemists have been on the lookout for high-oxidation-state iron complexes with metal-ligand multiple bonds because they are proposed intermediates in biocatalytic pathways, such as the enzymatic reduction of N₂ and O₂. Though several Fe(IV) and Fe(V) complexes have been prepared, only one Fe(VI) complex was known before now: the ferrate anion, FeO₄^2-, which serves as a useful oxidizing agent in several applications. John F. Berry and Karl Wieghardt at the Max Planck Institute for Bioinorganic Chemistry, in M?lheim an der Ruhr, Germany, and their colleagues now report the second Fe(VI) compound in the form of the iron nitride shown (Science, published online June 1, dx.doi.org/10.1126/sci ence.1128506). The complex was prepared from an Fe(III) azide complex, FeN₃L, where L is the trimethylcyclam acetate ligand. The Fe(III) complex was electrochemically oxidized to Fe(IV), then photochemically oxidized at 77 K to cleave N₂ and form the Fe(VI) complex, which remains stable at low temperature. Coupled with other recent advances, "these results portend both a much greater oxidation-state flexibility and multiple-bond chemistry for iron," notes MIT chemist Christopher C. Cummins.