Evgeny V. Kudrik

Novel Iron(III) Porphyrazine Complex. Complex Speciation and Reactions with NO and H2O2

The complex [iron(III) (octaphenylsulfonato)porphyrazine] (5-), Fe (III)(Pz), was synthesized. The p K a values of the axially coordinated water molecules were determined spectrophotometrically and found to be p K a 1 = 7.50 +/- 0.02 and p K a 2 = 11.16 +/- 0.06. The water exchange reaction studied by (17)O NMR as a function of the pH was fast at pH = 1, k ex = (9.8 +/- 0.6) x 10 (6) s (-1) at 25 degrees C, and too fast to be measured at pH = 10, whereas at pH = 13, no water exchange reaction occurred. The equilibrium between mono- and diaqua Fe (III)(Pz) complexes was studied at acidic pH as a function of the temperature and pressure. Complex-formation equilibria with different nucleophiles (Br (-) and pyrazole) were studied in order to distinguish between a five- (in the case of Br (-)) or six-coordinate (in the case of pyrazole) iron(III) center. The kinetics of the reaction of Fe (III)(Pz) with NO was studied as a model ligand substitution reaction at various pH values. The mechanism observed is analogous to the one observed for iron(III) porphyrins and follows an I d mechanism. The product is (Pz)Fe (II)NO (+), and subsequent reductive nitrosylation usually takes place when other nucleophiles like OH (-) or buffer ions are present in solution. Fe (III)(Pz) also activates hydrogen peroxide. Kinetic data for the direct reaction of hydrogen peroxide with the complex clearly indicate the occurrence of more than one reaction step. Kinetic data for the catalytic decomposition of the dye Orange II by H 2O 2 in the presence of Fe (III)(Pz) imply that a catalytic oxidation cycle is initiated. The peroxide molecule first coordinates to the iron(III) center to produce the active catalytic species, which immediately oxidizes the substrate. The influence of the catalyst, oxidant, and substrate concentrations on the reaction rate was studied in detail as a function of the pH. The rate increases with increasing catalyst and peroxide concentrations but decreases with increasing substrate concentration. At low pH, the oxidation of the substrate is not complete because of catalyst decomposition. The observed kinetic traces at pH = 10 and 12 for the catalytic cycle could be simulated on the basis of the obtained kinetic data and the proposed reaction cycle. The experimental results are in good agreement with the simulated ones.

Novel Reactivity of N‐Bridged Diiron Phthalocyanine in the Activation of CH Bonds: Hydroacylation of Olefins as an Example of the Efficient Formation of CC Bonds

Iron phthalocyanine complexes are versatile catalysts, in particular for selective oxidations and bleaching reactions, and they are readily available in terms of cost and accessibility at a large scale. Our research group has recently introduced N-bridged diiron phthalocyanines as efficient catalysts for oxidation. Preparation and spectroscopic studies of mnitrido bridged bimetallic complexes with phthalocyanine and porphyrin ligands have been described in the literature. In particular, these complexes containing FeACHTUNGTRENNUNG(+3.5)ACHTUNGTRENNUNG(mN)Fe ACHTUNGTRENNUNG(+3.5) unit were efficient in the mild oxidation of methane, benzene, and aromatic compounds. m-Oxo diiron phthalocyanine complexes were also shown to be efficient oxidation catalysts. All these examples report on the transformation of various C H bonds to C O and C=O functionalities. The selective formation of C C bonds through the activation of C H bonds is another challenging goal in synthetic chemistry. In the course of our research we have discovered an unexpected reactivity of m-nitrido-bisACHTUNGTRENNUNG[tetra(tert-butyl)phthalocyaninatoiron] (1) which can also be used as a catalyst for C C bond forming reactions. This novel approach is particularly useful for the hydroacylation of olefins, which is an important synthetic transformation that results in 100 % atom efficiency as the addition of an aldehyde to the double bond of an olefin affords a ketone containing all the atoms of both substrates. Ketones are important organic compounds widely used in the chemical industry as final products and as key synthetic precursors. These carbonyl compounds can be prepared by the oxidation of secondary alcohols, by the Friedel–Crafts acylation, by the reaction of acyl derivatives with organo-metallic reagents, or by hydroacylation of alkenes or alkynes with aldehydes. The latter approach is mainly promoted by rhodium or ruthenium complexes often applied in large amounts (up to 10–30 mol%). This reaction has often been limited by the tendency of the intermediate species to lose carbon oxide. An alternative approach is based on the generation of acyl radicals which attack the double bond of olefins. However, this method is the most successful with electron-poor olefins as substrates. There is an increasing demand for more general and sustainable approaches avoiding the use of organic solvents and large amounts of toxic catalysts. In addition, the replacement of expensive noble metal catalysts with more available and nontoxic catalysts is highly desirable. In this context, iron catalysts are especially attractive. Herein we report on the addition of acetaldehyde to unactivated cyclic or linear alkenes using low iron catalyst loading (0.01 mol %) performed in the absence of organic solvents (Scheme 1). This finding significantly increases the scope of application of these emerging binuclear catalysts.

Diiron N-bridged species bearing phthalocyanine ligand catalyzes oxidation of methane, propane and benzene under mild conditions

Transformation of methane, the most abundant and the least reactive compound of natural gas to valuable products is one of the most difficult chemical problems of great practical importance. In Nature, methane monooxygenase enzymes transform methane to methanol in water under physiological conditions. However, chemical analogs for such a transformation are unknown. Here, we show the mild and efficient aqueous oxidation of methane by hydrogen peroxide, an ecologically and biologically relevant oxidant catalyzed by supported μ-nitrido diiron phthalocyanine dimer, (FePctBu4)2N. This bio-inspired complex containing a stable Fe–N–Fe motif catalyzes the oxidation of methane to methanol which is further transformed to formaldehyde and formic acid as is demonstrated using 13CH4 and 18O labelling. (FePctBu4)2N-H2O2 system shows a high activity in the oxidation of benzene to phenol which occurs via formation of benzene oxide and exhibits NIH shift typically accociated with biological oxidation. Mechanistic features of oxidation of methane and benzene as well as detected intermediate hydroperoxo- and high valent oxo diiron complexes support an O-atom transfer reaction mechanism relevant to bio-oxidation.

Efficient epoxidation of olefins by H2O2 catalyzed by iron “helmet” phthalocyanines

High yields of epoxides were obtained in the oxidation of a large range of olefins using 1.2-2 equiv. of H2O2 in the presence of iron helmet phthalocyanines. The involvement of high-valent iron oxo species was evidenced using cryospray mass spectrometry.

Synthesis, mesomorphism and electrochemical properties of tetrasubstituted zinc and copper phthalocyanines

We describe the synthesis of highly soluble, tetrasubstituted zinc and copper phthalocyanines exhibiting liquid crystalline properties. These compounds were characterized using elemental analysis, MS, 1H-NMR, FTIR and UV-Vis absorption spectroscopy. The liquid crystalline properties of phthalocyanines (Pcs) were studied by polarizing optical microscopy and differential scanning calorimetry. All of the four compounds exhibit thermotropic columnar mesophases and two of them show clear hexagonal ordering. Additionally, these Pcs display lyotropic behaviour. The clearing temperatures lie above 300 °C and on cooling down the mesophase can be “frozen” into a glassy state. The cyclic voltammetry studies of these phthalocyanines show electrochemical stability and reversible redox behaviour. The Pcs without any azo groups in the ligands exhibit both reversible oxidation and reduction, whereas those with azo groups show only reversible reduction steps. The low HOMO energy values of about 5 eV as calculated from oxidation potential make these compounds interesting as p-type organic semiconductors for electro-optical applications.

Mesomorphism and Glass Formation of Phthalocyanine Metal Complexes with Bulky Substituents

This paper deals with the synthesis of phthalocyanine complexes, containing four oligo(oxyethylene)-, oxybenzene-, esther of p-oxybenzoic acid or p-oxyazobenzene side chains terminated by a bulky trityl substituent. Their purity was established by column chromatography and by satisfactory elemental analysis. The structures of resultant phthalocyanines were characterized by nuclear magnetic resonance (NMR), fast atom bombardment mass spectroscopy (FAB-MS), ultraviolet-visible (UV-VIS) and infrared (IR) spectroscopy and their phase transitions were studied by polarizing optical microscopy. Some of these complexes exhibit enantiotropic mesomorphic properties and transition into glass state on cooling. The glass appearance is influenced not only by side chains’ structure, but also by the nature of metal.

Stability and catalytic properties of μ-oxo and μ-nitrido dimeric iron tetrasulfophthalocyanines in the oxidation of Orange II by tert-butylhydroperoxide

A study of catalytic activity of μ-nitrido- and μ-oxo-dimeric iron tetrasulfophthalocyanines in the oxidation of Orange II by tert-butylhydroperoxide in aqueous solutions has been performed. It is shown that though in one catalytic cycle activity of μ-oxo-dimer is higher, stability of this complex in oxidative conditions is poor. μ-nitrido-dimer combines relatively good catalytic activity with very high stability in the presence of tert-butylhydroperoxide. The mechanisms of oxidative decomposition of dimers and catalytic oxidation of Orange II have been proposed on the base of kinetic results. The products of catalytic processes are shown to be bio-degradable non-toxic small organic compounds.

Solvent-dependent rotational phenomena in μ-nitrido-[2,3,9,10,16,17,23,24-octa(n-pentoxy)phthalocyaninato]diiron complex

The syntheses and spectroscopic properties of new μ-nitrido-[2,3,9,10,16,17,23,24-octa(n-pentoxy)phthalocyaninato]diiron complexes in Fe(IV)Fe(IV) and Fe(+3.5)Fe(+3.5) oxidation states are reported. UV-vis spectra of both dimers demonstrate a strong solvatochromic behavior. UV-vis and 1H NMR data reveal the presence of two different forms for both oxidation states in apolar and polar solvents. Fe K-edge X-ray absorption near-edge structures (XANES) spectra of two Fe(IV)Fe(IV) forms also show a significant difference: pre-edge feature in toluene is shifted to higher energy compared to that in tetrahydrofuran. The difference of properties between two forms is explained by solvent-dependent mutual orientation of two phthalocyanine rings. A strong sharp Q-band in UV-vis spectrum at 642 nm and small splitting of aromatic protons (0.18 ppm) in 1H NMR spectrum observed in apolar solvents (toluene, benzene, cyclohexane) imply that the green form is in more symmetric D4d configuration. In turn, a broad multipreaked Q-band and relatively high splitting of aromatic protons (0.56 ppm) observed in THF and CH2Cl2 for the blue form are in agreement with less symmetric D4 conformation. The Fe(μ-N)Fe structure is relatively rigid showing no free rotation at room temperature in NMR time scale. Tuning of the structure of N-bridged diiron macrocyclic complexes by introduction of substituents and modification of electronic properties of the complexes via conformation changes might be useful for optimization of their catalytic properties as well as for their potential application in sensors.

Reactions of methyl viologen and nitrite with thiourea dioxide. New opportunities for an old reductant

Thiourea dioxide was used as a precursor for sulfoxylate, SO22−, which is shown to reduce the methyl viologen dication to the fully reduced form, this is the first example of a direct study of the reduction with sulfoxylate; an important advantage of sulfoxylate and its parent compound thiourea dioxide, is their ability to reduce nitrite (the final product being nitrogen) and nitrous oxide in alkaline solutions in the absence of a catalyst.

Synthesis and Induction of Mesomorphic Properties of Tetrabenzoporphine Derivatives

Zinc complexes of meso-alkyl-substituted tetrabenzoporphines and their aza-derivatives have been synthesized using the interaction of phthalimide or its derivatives with zinc salts of the carboxylic acids. The porphyrin-ligands were obtained on the basis of the above mentioned compounds. The spectral and mesomorphic properties of the synthesized compounds were studied.