M. R. Anneser, S. Haslinger, A. Pöthig, M. Cokoja, V. D'Elia, M. P. Högerl, J. M. Basset and F. E. Kühn
Dalton Trans., Advance Article, (2016)
The dioxygen reactivity of a cyclic iron(II)
tetra–NHC-complex (NHC: N-heterocyclic carbene) is investigated.
Divergent oxidation behavior is observed depending on the choice of the
solvent (acetonitrile or acetone). In the first case, exposure to
molecular oxygen leads to an oxygen free Fe(III) whereas in the latter case an oxide bridged Fe(III) dimer is formed. In acetone, an Fe(III)-superoxide can be trapped, isolated and characterized as intermediate at low temperatures. An Fe(III)–O–Fe(III) dimer is formed from the Fe(III)
superoxide in acetone upon warming and the molecular structure has been
revealed by single crystal X-ray diffraction. It is shown that the
oxidation of the Fe(II) complex in both solvents is a reversible process. For the regeneration of the initial Fe(II) complex both organic and inorganic reducing agents can be used.