Intermediate-spin iron(iv)-oxido species with record reactivity

The nonheme iron(iv)-oxido complex trans-N3-[(L-1)Fe-IV = O(Cl)](+), where L-1 is a derivative of the tetradentate bispidine 2,4-di(pyridine-2-yl)-3,7-diazabicyclo[3.3.1]nonane-1-one, has an S = 1 electronic ground state and is the most reactive nonheme iron model system known so far, of a similar order of reactivity as nonheme iron enzymes (C-H abstraction of cyclohexane, -90 degrees C (propionitrile), t(1/2) = 3.5 s). The reaction with cyclohexane selectively leads to chlorocyclohexane, but cage escape at the [(L-1)Fe-III(OH)(Cl)](+)/cyclohexyl radical intermediate lowers the productivity. Ligand field theory is used herein to analyze the d-d transitions of [(L-1)(FeO)-O-IV(X)](n+) (X = Cl-, Br-, MeCN) in comparison with the thoroughly characterized ferryl complex of tetramethylcyclam (TMC = L-2; [(L-2)(FeO)-O-IV(MeCN)](2+)). The ligand field parameters and d-d transition energies are shown to provide important information on the triplet-quintet gap and its correlation with oxidation reactivity.

Automated summary

The study focuses on the reactivity and comparison with hemoglobin iron enzymes of a nonheme iron (IV)-oxido complex.