Catalytic defluorination of perfluorinated aromatics under oxidative conditions using N-bridged diiron phthalocyanine.

Carbon-fluorine bonds are the strongest single bonds in organic chemistry, making activation and cleavage usually associated with organometallic and reductive approaches particularly difficult. We describe here an efficient defluorination of poly- and perfluorinated aromatics under oxidative conditions catalyzed by the µ-nitrido diiron phthalocyanine complex [(Pc)Fe(III)(µ-N)Fe(IV)(Pc)] under mild conditions (hydrogen peroxide as the oxidant, near-ambient temperatures). The reaction proceeds via the formation of a high-valent diiron phthalocyanine radical cation complex with fluoride axial ligands, [(Pc)(F)Fe(IV)(µ-N)Fe(IV)(F)(Pc(+•))], which was isolated and characterized by UV-vis, EPR, (19)F NMR, Fe K-edge EXAFS, XANES, and Kß X-ray emission spectroscopy, ESI-MS, and electrochemical techniques. A wide range of per- and polyfluorinated aromatics (21 examples), including C6F6, C6F5CF3, C6F5CN, and C6F5NO2, were defluorinated with high conversions and high turnover numbers. [(Pc)Fe(III)(µ-N)Fe(IV)(Pc)] immobilized on a carbon support showed increased catalytic activity in heterogeneous defluorination in water, providing up to 4825 C-F cleavages per catalyst molecule. The µ-nitrido diiron structure is essential for the oxidative defluorination. Intramolecular competitive reactions using C6F3Cl3 and C6F3H3 probes indicated preferential transformation of C-F bonds with respect to C-Cl and C-H bonds. On the basis of the available data, mechanistic issues of this unusual reactivity are discussed and a tentative mechanism of defluorination under oxidative conditions is proposed.

X-ray absorption and emission spectroscopies of X-bridged diiron phthalocyanine complexes (FePc)2X (X = C, N, O) combined with DFT study of (FePc)2X and their high-valent diiron oxo complexes.

µ-Nitrido diiron phthalocyanine [PcFe(+3.5)NFe(+3.5)Pc](0) is an efficient catalyst, able to catalyze the oxidation of methane under near-ambient conditions. In this work, we compared the properties of structurally similar µ-carbido (1), µ-nitrido (2), and µ-oxo (3) dimers of iron phthalocyanine. The goal was to discern the structural and electronic differences between these complexes and to propose a rationale for the exceptional activity of 2. Extended X-ray fine-structure spectroscopy, high-resolution X-ray emission spectroscopy, and resonant inelastic X-ray scattering were applied to study the geometry and electronic structure of iron species in the series 1-3. The data provided by core hole spectroscopies were compared to the results of DFT calculations and found to coherently describe the structural and electronic properties of 1-3 as having equivalent iron centers with formal iron oxidation degrees of 3, 3.5, and 4 for the µ-oxo, µ-nitrido, and µ-carbido dimers, respectively. However, the bond length to the bringing atom changed in an unexpected sequence Fe-O > Fe-N < Fe-C, indicating redox non-innocence of the brigding µ-carbido ligand in 1. According to the X-ray emission spectroscopy, the µ-nitrido dimer 2 is a low-spin compound, with the highest covalency in the series 1-3. The DFT-calculated geometry and electronic structures as well as core hole spectra of hypothetical high-valent oxo complexes of 1-3 were compared, in order to explain the particular catalytic activity of 2 and to estimate the prospects of spectroscopic observation of such species. It appears that the terminal Fe═O bond is the longest in the oxo complex of 2, due to the strong trans-effect of the nitrido ligand. The corresponding LUMO of the µ-nitrido diiron oxo complex has the lowest energy among the three oxo complexes. Therefore, the oxo complex of 2 is expected to have the highest oxidative power.

Synthesis, X-ray crystal structure, UV/visible linear and nonlinear (optical limiting) spectral properties of symmetrical and unsymmetrical porphyrazines with annulated 1,2,5-thiadiazole and 1,4-diamyloxybenzene moieties.

Co-cyclization of 1,2,5-thiadiazole-3,4-dicarbonitrile and 3,6-diamyloxyphthalodinitrile in the presence of magnesium or lithium amylate in amyl alcohol leads to mixtures containing the Mg derivatives of the symmetrical species tetrakis(1,2,5-thiadiazolo)porphyrazine, (S(4))PzH(2), and tetrakis(1,4-diamyloxybenzo)porphyrazine, (A(4))PzH(2), and the low-symmetry macrocycles bearing peripheral 1,2,5-thiadiazole and 1,4-diamyloxybenzene rings in the ratio 1:3, 2:2 (cis and trans), and 3:1, that is, (SA(3))PzH(2), (S(2)A(2))PzH(2), (SASA)PzH(2), and (S(3)A)PzH(2), respectively. The basic Mg materials were converted to the corresponding free-base macrocycles by treatment with CF(3)COOH. The species were separated from the mixtures by chromatography, either as Mg complexes or demetalated materials. With results on (S(4))PzH(2) and (SA(3))PzH(2) in hand, including crystallographic work on the latter, a general chemical physical investigation has been carried out of all the symmetrical and unsymmetrical free-base macrocycles. The structures of the species (S(2)A(2))PzH(2) and (A(4))PzH(2). were elucidated by single-crystal X-ray crystallography. The effect of the progressive variation of the macrocyclic structure along the series, from the symmetrical (S(4))PzH(2) to its symmetrical partner (A(4))PzH(2) via the low-symmetry 3:1, 2:2 (cis and trans), and 1:3 macrocycles, was studied by IR, (1)H NMR, and UV/Vis linear and nonlinear (optical limiting) measurements. The results are interpreted on the basis of intra- and intermolecular interactions between the electron-deficient 1,2,5-thiadiazole and the electron-donating 1,4-diamyloxybenzene moieties.