Photochemical generation and reactivity of a new phthalocyanine-manganese-oxo intermediate

The first phthalocyanine-manganese-oxo intermediate was successfully generated by visible-light photolysis of chlorate or nitrite manganese(III) precursors, and its reactivity towards organic substrates was kinetically probed and compared with other related porphyrin-metal-oxo intermediates.

Comparing the reactivity of an oxoiron(IV) cation radical and its oxoiron(V) tautomer towards C-H bonds

An oxoiron(IV) cation radical is generated upon two-electron oxidation of an iron(III) complex bearing an electron-rich methoxy substituted bTAML framework and thoroughly characterized via multiple spectroscopic techniques and density functional theory (DFT). Reactivity studies demonstrate faster rates for oxidation of strong aliphatic sp³ C-H bonds than for its corresponding oxoiron(V) valence tautomer.

Site-Selective Supramolecular Complexation Activates Catalytic Ethane Oxidation by a Nitrido-Bridged Iron Porphyrinoid Dimer

Development of supramolecular methods to further activate a highly reactive intermediate is a fascinating strategy to create novel potent catalysts for activation of inert chemicals. Herein, a supramolecular approach to enhance the oxidizing ability of a high-valent oxo species of a nitrido-bridged iron porphyrinoid dimer that is a known potent molecular catalyst for light alkane oxidation is reported. For this purpose, a nitrido-bridged dinuclear iron complex of porphyrin-phthalocyanine heterodimer 3⁵⁺ , which is connected through a fourfold rotaxane, was prepared. Heterodimer 3⁵⁺ catalyzed ethane oxidation in the presence of H₂ O₂ at a relatively low temperature. The site-selective complexation of 3⁵⁺ with an additional anionic porphyrin (TPPS^4- ) through π-π stacking and electrostatic interactions afforded a stable 1:1 complex. It was demonstrated that the supramolecular post-synthetic modification of 3⁵⁺ enhances its catalytic activity efficiently. Moreover, supramolecular conjugates achieved higher catalytic ethane oxidation activity than nitrido-bridged iron phthalocyanine dimer, which is the most potent iron-oxo-based molecular catalyst for light-alkane oxidation reported so far. Electrochemical measurements proved that the electronic perturbation from TPPS^4- to 3⁵⁺ enhanced the catalytic activity.

Reactive Cobalt⁻Oxo Complexes of Tetrapyrrolic Macrocycles and N-based Ligand in Oxidative Transformation Reactions

High-valent cobalt–oxo complexes are reactive transient intermediates in a number of oxidative transformation processes e.g., water oxidation and oxygen atom transfer reactions. Studies of cobalt–oxo complexes are very important for understanding the mechanism of the oxygen evolution center in natural photosynthesis, and helpful to replicate enzyme catalysis in artificial systems. This review summarizes the development of identification of high-valent cobalt–oxo species of tetrapyrrolic macrocycles and N-based ligands in oxidation of organic substrates, water oxidation reaction and in the preparation of cobalt–oxo complexes.

Heteroleptic μ-nitrido diiron complex supported by phthalocyanine and octapropylporphyrazine ligands: Formation of oxo species and their reactivity with fluorinated compounds

The synthesis and reactivity of [Formula: see text]-bridged diiron macrocyclic complexes have been a topic of increasing interest in recent years since the observation of particular catalytic properties of these complexes. Herein, we report a preparation of a novel heteroleptic μ-nitrido diiron complex with unsubstituted phthalocyanine and octapropylporphyrazine macrocycles. This complex reacts with [Formula: see text]-chloroperbenzoic acid to form high-valent diiron oxo species showing strong oxidizing properties. The formation and structure of the transient oxo species was investigated by cryospray collision induced dissociation MS/MS technique. Analysis of fragmentation pattern showed that the attachment of oxo moiety occurred at either iron phthalocyanine or at iron porphyrazine site with slight preference for the phthalocyanine iron site. The catalytic properties of the heteroleptic μ-nitrido diiron complex were evaluated in the oxidative transformation of hexafluorobenzene and perfluoro(allylbenzene).

Iron phthalocyanine supported on amidoximated PAN fiber as effective catalyst for controllable hydrogen peroxide activation in oxidizing organic dyes

Iron(II) phthalocyanine was immobilized onto amidoximated polyacrylonitrile fiber to construct a bioinspired catalytic system for oxidizing organic dyes by H₂O₂ activation. The amidoxime groups greatly helped to anchor Iron(II) phthalocyanine molecules onto the fiber through coordination interaction, which has been confirmed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and UV-vis diffuse reflectance spectroscopy analyses. Electron spin resonance studies indicate that the catalytic process of physically anchored Iron(II) phthalocyanine performed via a hydroxyl radical pathway, while the catalyst bonded Iron(II) phthalocyanine through coordination effect could selectively catalyze the H₂O₂ decomposition to generate high-valent iron-oxo species. This may result from the amidoxime groups functioning as the axial fifth ligands to favor the heterolytic cleavage of the peroxide OO bond. This feature also enables the catalyst to only degrade the dyes adjacent to the catalytic active centers and enhances the efficient utilization of H₂O₂. In addition, this catalyst could effectively catalyze the mineralization of organic dyes and can be easily recycled without any loss of activity.

Reduction of (chloro)-μ-nitrido-bis[(tetra-tert-butyl-phthalocyaninato)iron(IV)] with organic N-bases

The interaction of (chloro)-[Formula: see text]-nitrido-bis[(tetra-tert-butyl-phthalocyaninato)iron(IV)] Cl(FePc)2N with organic [Formula: see text]-bases L as electron–donors (L [Formula: see text] diethylamine, imidazole, 1-methylimidazole, 2-methylimidazole) with the formation of one-electron reduced species (L)PcFe[Formula: see text]–N[Formula: see text]Fe[Formula: see text]Pc(L) was investigated in benzene at 298 K by UV-visible spectroscopy. The reaction was established to be stepwise process including fast reversible axial binding of two substrate molecules onto iron cations followed by slow one-electron metal-centered reduction. The results of IR, ESI-MS and EPR study support the formation of final product with Fe[Formula: see text]–N[Formula: see text]Fe[Formula: see text] unit and two substrate molecules in the first coordination sphere. The reaction kinetics was studied, the pre-equilibrium constants [Formula: see text] and rate constants [Formula: see text] were obtained. The [Formula: see text] and [Formula: see text] values were found to be linearly correlated with basicity of substrates p[Formula: see text]. The possibility of the transition Fe[Formula: see text] Fe[Formula: see text] is promoted by electron–donor properties of substrate combined with the presence of both electron-rich macrocycle and [Formula: see text]-backdonation Fe [Formula: see text] N[Formula: see text].

μ-Nitrido Diiron Macrocyclic Platform: Particular Structure for Particular Catalysis

The ultimate objective of bioinspired catalysis is the development of efficient and clean chemical processes. Cytochrome P450 and soluble methane monooxygenase enzymes efficiently catalyze many challenging reactions. Extensive research has been performed to mimic their exciting chemistry, aiming to create efficient chemical catalysts for functionalization of strong C-H bonds. Two current biomimetic approaches are based on (i) mononuclear metal porphyrin-like complexes and (ii) iron and diiron non-heme complexes. However, biomimetic catalysts capable of oxidizing CH4 are still to be created. In the search for powerful oxidizing catalysts, we have recently proposed a new bioinspired strategy using N-bridged diiron phthalocyanine and porphyrin complexes. This platform is particularly suitable for stabilization of Fe(IV)Fe(IV) complexes and can be useful to generate high-valent oxidizing active species. Indeed, the possibility of charge delocalization on two iron centers, two macrocyclic ligands, and the nitrogen bridge makes possible the activation of H2O2 and peracids. The ultrahigh-valent diiron-oxo species (L)Fe(IV)-N-Fe(IV)(L(+•))═O (L = porphyrin or phthalocyanine) have been prepared at low temperatures and characterized by cryospray MS, UV-vis, EPR, and Mössbauer techniques. The highly electrophilic (L)Fe(IV)-N-Fe(IV)(L(+•))═O species exhibit remarkable reactivity. In this Account, we describe the catalytic applications of μ-nitrido diiron complexes in the oxidation of methane and benzene, in the transformation of aromatic C-F bonds under oxidative conditions, in oxidative dechlorination, and in the formation of C-C bonds. Importantly, all of these reactions can be performed under mild and clean conditions with high conversions and turnover numbers. μ-Nitrido diiron species retain their binuclear structure during catalysis and show the same mechanistic features (e.g., (18)O labeling, formation of benzene epoxide, and NIH shift in aromatic oxidation) as the enzymes operating via high-valent iron-oxo species. μ-Nitrido diiron complexes can react with perfluorinated aromatics under oxidative conditions, while the strongest oxidizing enzymes cannot. Advanced spectroscopic, labeling, and reactivity studies have confirmed the involvement of high-valent diiron-oxo species in these catalytic reactions. Computational studies have shed light on the origin of the remarkable catalytic properties, distinguishing the Fe-N-Fe scaffold from Fe-C-Fe and Fe-O-Fe analogues. X-ray absorption and emission spectroscopies assisted with DFT calculations allow deeper insight into the electronic structure of these particular complexes. Besides the novel chemistry involved, iron phthalocyanines are cheap and readily available in bulk quantities, suggesting high application potential. A variety of macrocyclic ligands can be used in combination with different transition metals to accommodate M-N-M platform and to tune their electronic and catalytic properties. The structural simplicity and flexibility of μ-nitrido dimers make them promising catalysts for many challenging reactions.

Catalytic degradation of recalcitrant pollutants by Fenton-like process using polyacrylonitrile-supported iron (II) phthalocyanine nanofibers: Intermediates and pathway

Iron (II) phthalocyanine (FePc) molecules were isolated in polyacrylonitrile (PAN) nanofibers by electrospinning to prevent the formation of dimers and oligomers. Carbamazepine (CBZ) and Rhodamine B (RhB) degradation was investigated during a Fenton-like process with FePc/PAN nanofibers. Classical quenching tests with isopropanol and electron paramagnetic resonance tests with 5,5-dimethyl-pyrroline-oxide as spin-trapping agent were performed to determine the formation of active species during hydrogen peroxide (H2O2) decomposition by FePc/PAN nanofibers. After eight recycles for CBZ degradation over the FePc/PAN nanofibers/H2O2 system, the removal ratios of CBZ remained at 99%. Seven by-products of RhB and twelve intermediates of CBZ were identified using ultra-performance liquid chromatography and high-resolution mass spectrometry. Pathways of CBZ and RhB degradation were proposed based on the identified intermediates. As the reaction proceeded, all CBZ and RhB aromatic nucleus intermediates decreased and were transformed to small acids, but also to potentially toxic epoxide-containing intermediates and acridine, because of the powerful oxidation ability of •OH in the catalytic system.

Site-selective formation of an iron(iv)-oxo species at the more electron-rich iron atom of heteroleptic μ-nitrido diiron phthalocyanines

A combination of MS and computation on μ-nitrido bridged diiron complexes reveals H₂O₂ binding to the complex and generates an oxidant capable of oxidizing methane.

Iron(iv)–oxo species have been identified as the active intermediates in key enzymatic processes, and their catalytic properties are strongly affected by the equatorial and axial ligands bound to the metal, but details of these effects are still unresolved. In our aim to create better and more efficient oxidants of H-atom abstraction reactions, we have investigated a unique heteroleptic diiron phthalocyanine complex. We propose a novel intramolecular approach to determine the structural features that govern the catalytic activity of iron(iv)–oxo sites. Heteroleptic μ-nitrido diiron phthalocyanine complexes having an unsubstituted phthalocyanine (Pc1) and a phthalocyanine ligand substituted with electron-withdrawing alkylsulfonyl groups (PcSO₂R) were prepared and characterized. A reaction with terminal oxidants gives two isomeric iron(iv)–oxo and iron(iii)–hydroperoxo species with abundances dependent on the equatorial ligand. Cryospray ionization mass spectrometry (CSI-MS) characterized both hydroperoxo and diiron oxo species in the presence of H₂O₂. When m-CPBA was used as the oxidant, the formation of diiron oxo species (PcSO₂R)FeNFe(Pc1) Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O was also evidenced. Sufficient amounts of these transient species were trapped in the quadrupole region of the mass-spectrometer and underwent a CID-MS/MS fragmentation. Analyses of fragmentation patterns indicated a preferential formation of hydroperoxo and oxo moieties at more electron-rich iron sites of both heteroleptic μ-nitrido complexes. DFT calculations show that both isomers are close in energy. However, the analysis of the iron(iii)–hydroperoxo bond strength reveals major differences for the (Pc1)FeN(PcSO₂R)Fe^IIIOOH system as compared to (PcSO₂R)FeN(Pc1)Fe^IIIOOH system, and, hence binding of a terminal oxidant will be preferentially on more electron-rich sides. Subsequent kinetics studies showed that these oxidants are able to even oxidize methane to formic acid efficiently.

A Mild Catalytic Oxidation System: FePcOTf/H2O2 Applied for Cyclohexene Dihydroxylation

Iron (III) phthalocyanine complexes were employed for the first time as a mild and efficient Lewis acid catalyst in the selective oxidation of cyclohexene to cyclohexane-1,2-diol. It was found that the catalyst FePcOTf shown excellent conversion and moderate selectivity relative to other iron (III) phthalocyanine complexes. The optimum conditions of the oxidation reaction catalyzed by FePcOTf/H₂O₂ have been researched in this paper. Iron (III) phthalocyanine triflate (1 mol %) as catalyst, hydrogen peroxide as oxidant, methanol as solvent, and a mole ratio of substrate and oxidant (H₂O₂) of 1:1 were used for achieving moderate yields of 1,2-diols under reflux conditions after eight hours.

Interfacial peroxidase-like catalytic activity of surface-immobilized cobalt phthalocyanine on multiwall carbon nanotubes

The rapid diffusional mass transfer process (DMTP) always results in a highly efficient reaction.

μ-Nitrido diiron octaethylporphyrin complex: synthesis and properties

μ-nitrido diiron porphyrin complex ( OEPFe )2 N (OEP = octaethylporphyrinato dianion) was synthesized by the treatment of ( OEPFe ) Cl with hydrazoic acid followed by the thermal decomposition of formed ( OEPFe ) N 3 complex. The ( OEPFe )2 N complex was investigated by UV-vis, IR, HR ESI-TOF MS and EPR spectroscopic methods. EXAFS study indicated a very short Fe – Fe distance of 3.30 Å in this dimer compared with 3.48 Å distance between iron sites in the related μ-nitrido diiron complex on the tetraphenylporphyrin platform. This difference can be explained by the steric hindrance exerted by phenyl substituents in the latter. The spectral properties of the ( OEPFe )2 N complex are discussed. The catalytic properties of ( OEPFe )2 N were evaluated in the oxidation of cyclohexene and cyclohexane.