Journal of the American Chemical Society, Vol.116, No.20, 9141-9149, 1994
Synthesis and Electrochemistry of Iron(III) Corroles Containing a Nitrosyl Axial Ligand - Spectral Characterization of ((Oec)Fe-III(No))(N) Where N=0, 1, 2, or -1 and Oec Is the Trianion of 2,3,7,8,12,13,17,18-Octaethylcorrole
The synthesis, structural and spectral characterization of(OEC)Fe(NO) and [(OEC)Fe(NO)](+) where OEC is the trianion of 2,3,7,8,12,13,17,18-octaethylcorrole, is reported. To our knowledge, (OEC)Fe-III(NO) is the first example of a neutral air-stable iron(III) nitrosyl tetrapyrrole. It undergoes up to three oxidations and two reductions in nonaqueous media. The first two oxidations and both reductions are reversible and are located at E(1/2) = +0.61, +1.14, -0.41, and -1.92 V vs SCE in benzonitrile containing 0.1 M tetra-n-butylammonium perchlorate. The two oxidations involve the stepwise abstraction of a single electron from the corrole macrocycle and generate a stable iron(III) pi-cation radical and dication, both of which still contain a coordinated NO axial ligand. The two one-electron reductions of (OEC)Fe-III(NO) are also reversible and proceed without loss of the axial NO ligand. The first two oxidations and the first reduction of (OEC)Fe(NO) give products which are sufficiently stable to be spectroscopically characterized by UV-visible, IR, and/or ESR spectroscopy after in situ generation in PhCN or CH2Cl2. The ESR spectrum of the singly reduced product shows three g values at 2.00, 2.04, and 2.08 with nitric oxide N-14 hyperfine splitting in each region. This spectrum is quite similar to the one reported for five-coordinate (TPP)Fe-II(NO) in toluene glass at 120 K and also resembles the spectra of various hemoproteins containing iron(II) with bound NO. This result is consistent with formation of a five-coordinate iron(II) macrocycle containing a bent MNO unit which is formulated as [(OEC)Fe-II(NO)](-). The thin-layer FTIR spectral changes obtained during the first electroreduction are also consistent with formation of [(OEC)Fe-II(NO)](-).
Keywords:PI-CATION RADICALS;NITRIC-OXIDE SYNTHASE;REDUCTASE MODEL COMPOUNDS;ELECTRON-SPIN-RESONANCE;MOLECULAR STEREOCHEMISTRY;IRON PORPHYRIN;L-ARGININE;ELECTROCATALYTIC REDUCTION;COBALT PORPHYRINS;NONAQUEOUS MEDIA