Organometallic μ-Nitridodiiron Complexes in Oxidation States Ranging from (III/III) to (IV/IV).

Iron complexes with nitrido ligands are of interest as molecular analogues of key intermediates during N-to-NH conversion in industrial or enzymatic processes. Dinuclear iron complexes with a bridging nitrido unit are mostly known in relatively high oxidation states (III/IV or IV/IV), originating from the decomposition of azidoiron precursors via high-valent Fe≡N intermediates. The use of a tetra-NHC macrocyclic scaffold ligand (NHC = N-heterocyclic carbene) has now allowed for the isolation of a series of organometallic μ-nitridodiiron complexes ranging from the mid-valent Fe-N-Fe () via mixed-valent Fe-N-Fe (type ) to the high-valent Fe-N-Fe (type ) species that are interconverted at moderate potentials, accompanied by axial ligand binding at the Fe sites.

Functional Models for the Mono- and Dinitrosyl Intermediates of FNORs: Semireduction versus Superreduction of NO.

The reduction of NO to NO by flavodiiron nitric oxide reductases (FNORs) is related to the disruption of the defense mechanism in mammals against invading pathogens. The proposed mechanism for this catalytic reaction involves both nonheme mono- and dinitrosyl diiron(II) species as the key intermediates. Recently, we reported an initial account for NO reduction activity of an unprecedented mononitrosyl diiron(II) complex, [Fe(-Et-HPTB)(NO)(DMF)](BF) () (-Et-HPTB is the anion of N,N,N',N'-tetrakis(2-(l-ethylbenzimidazolyl))-2-hydroxy-1,3-diaminopropane; DMF = dimethylformamide) with [Fe{FeNO}] formulation [Jana et al.

Disproportionation Equilibrium of a μ-Oxodiiron(III) Complex Giving Rise to C-H Activation Reactivity: Structural Snapshot of a Unique Oxoiron(IV) Adduct.

μ-Oxodiiron(III) species are air-stable and unreactive products of autoxidation processes of monomeric heme and non-heme iron(II) complexes. Now, the organometallic [(L )Fe -(μ-O)-Fe (L )] complex 1 (L is a macrocyclic tetracarbene) is shown to be reactive in C-H activation without addition of further oxidants. Studying the oxidation of dihydroanthracene, it was found that 1 thermally disproportionates in MeCN solution into its oxoiron(IV) (2) and iron(II) components; the former is the active species in the observed oxidation processes.

Spin-State Variations of Iron(III) Complexes with Tetracarbene Macrocycles.

Starting from their six-coordinate iron(II) precursor complexes [L Fe(MeCN)] , a series of iron(III) complexes of the known macrocyclic tetracarbene ligand L and its new octamethylated derivative L , both providing four imidazol-2-yliden donors, were synthesized. Several five- and six-coordinate iron(III) complexes with different axial ligands (Cl , OTf , MeCN) were structurally characterized by X-ray diffraction and analyzed in detail with respect to their spin state variations, using a bouquet of spectroscopic methods (NMR, UV/Vis, EPR, and Fe Mößbauer). Depending on the axial ligands, either low-spin (S=1/2) or intermediate-spin (S=3/2) states were observed, whereas high-spin (S=5/2) states were inaccessible because of the extremely strong in-plane σ-donor character of the macrocyclic tetracarbene ligands.