Designing a dimeric phthalocyanine-supported catalyst for the selective oxidation of aromatic compounds

The synthesis of new modified phthalocyanine-supported catalysts has been designed in order to stabilise more active and selective dimeric form by the covalent link of two phthalocyanine molecules through N,N′-diethyl-1,3-propanediamine spacer. The catalytic performance of these modified supported catalysts was tested for the aromatic oxidation of 2,3,6-trimethylphenol (TMP), naphthalene, 2-methylnaphthalene (2MN) and 2,3-dimethylnaphthalene and compared with that of iron phthalocyanine-supported catalysts having SO₃H, SO₂OSiPh₃ and SO₂NⁱPr₂ substituents on the grafted phthalocyanine. Diamine modified catalyst was more active and selective in the oxidation of the above substrates to corresponding quinones. Trimethyl-1,4-benzoquinone (precursor of vitamin E) was obtained with 84 % yield at 96 % conversion of TMP. More demanding oxidation of 2MN afforded 34 % yield of 2-methyl-1,4-naphthoquinone (vitamin K₃).     

Spectroscopic and magnetic properties of a new class of two-dimensional bitriazole compounds: The X-ray structure of poly-bis(thiocyanato-N)-bis-μ-(4,4′-bis-1,2,4-triazole-N1,N1′)-cobalt(II) monohydrate

The synthesis of a new class of two-dimensional triazole compounds is described, including the crystal structure of [Co(NCS)₂(btr)₂]H₂O [btr stands for 4,4′-bis-1,2,4-triazole (C₄H₄N₆)]. Crystals are monoclinic, space group C2/c, a = 11.159(1) Å, b = 13.047(4) Å, c = 12.993(3) Å, β = 91.81(2)°, Z = 4. The structure has been solved by Fourier and direct methods and refined by full-matrix least squares to R = 0.0229, R_w = 0.0283. The structure consists of layers of six-coordinated cobalt atoms, each having two trans-oriented N-bonded thiocyanate groups [CoNCS 2.098(2) Å] and linked together in the equatorial plane by single bridges of btr to a two-dimensional network. The btr ligand coordinates through its N(1) and N(1′) atoms [CoN 2.128(1) and 2.142(1) Å]. The intralayer CoCo distance is 9.207(2) Å, and the inter-layer CoCo distance is 8.584(1) Å. The magnetic susceptibilities of the compound and of the isostructural nickel and iron compounds are discussed. The iron compound exhibits a high-spin-low-spin crossover at liquid-nitrogen temperatures, as shown by magnetic susceptibility.     

New phenanthroline iron complexes: Synthesis and catalytic activity in alkane oxidation with hydrogen peroxide

New binuclear iron complexes with labile coordination sites, [Fe₂OL₄(H₂O)₂](ClO₄)₄ where L stands for hydrophobic phenanthroline (phen) bearing electronegative and lipophilic substituents (Cl, Br, C₂H₅, C₆H₅, C₆H₁₃), are synthesized. The stereospecificity, alcohol/ketone ratio, regioselectivity, and substituent effect in the hydroxylation of alkanes (cyclohexane, adamantane, cis-1,2-dimethylcyclohexane) with hydrogen peroxide catalyzed by these complexes are studied. The said parameters, as well as a decrease in the alkane oxidation regioselectivity with increasing hydrogen peroxide concentration, are similar to the respective parameters for mononuclear iron complexes of tetradentate ligands. The results confirm that regardless of the nature of chelating ligands, the same mechanism operates in both cases, namely, the transfer of an oxygen atom with the participation of ferryl intermediates.     

Selective gas-phase oxidation of pyridine derivatives with hydrogen peroxide

The interfering kinetics of the synchronous reactions of hydrogen peroxide decomposition and the oxidation of pyridine derivatives have been studied experimentally. The regions of the selective oxidation of the pyridine derivatives have been found, and the optimal conditions for the production of 4-vinylpyridine, 4-vinylpyridine N-monoxide, 2,2-dipyridyl, and pyridine have been determined. The most probable synchronization mechanism is suggested for hydrogen peroxide decomposition and the free-radical chain oxidation of pyridine derivatives. The HO ₂ ^· radical plays the key role in this mechanism. The activation energies are calculated for the elementary steps of 4-ethylpyridine dehydrogenation.     

Studies on thermal oxidation of chalcopyrite from Chitradurga,Karnataka State,India

When chalcopyrite is heated in air, up to 350? there is no marked change. Between 350 and 440?, surface material is oxidised to iron sulphate, CuSO₄ and Fe₂O₃, while in regions not accessible to oxygen the formation of Cu₅FeS₄, FeS and S takes place. From 440 to 500? oxidation and sulphation phenomena occur. Stable compounds between 500 and 650? are iron sulphate, CuSO₄ and Fe₄O₃, with a minor amount of 6CuO.Cu₂O indicated at 650?. After the decomposition of iron sulphate, CuSO₄ decomposes, first to CuO.CuSO₄ and then to CuO. By 750? the sulphur has been totally lost from all compounds, while the oxides of copper and iron partly react to form CuFe₂O₄. Final products of oxidation between 800 and 850? are CuO, CuFe₂O₄ and Fe₃O₄.     

Thermal decomposition study and biological characterization of zinc(II) 2-chlorobenzoate complexes with bioactive ligands

New zinc(II) 2-chlorobenzoates of general formula [Zn(2-ClC₆H₄COO)₂(L)₂] (where L = caffeine—caf, urea—u, methyl-3-pyridylcarbamate—mpc, phenazone—phen, theophylline—thp) were synthesised and characterised by elemental analysis and IR spectroscopy. The thermal behaviour of the complexes was studied by TG/DTG and DTA methods in nitrogen and in air atmosphere. During the thermal decomposition of the studied compounds the release of organic ligands take place followed by the decomposition of 2-chlorobenzoate anion. The volatile decomposition intermediates were proved by mass spectrometry. Zinc oxide was found as the final product of the thermal decomposition performed up to 1,000 K. The antimicrobial activity of the zinc(II) complexes against various strains of bacteria, yeasts and filamentous fungi has been investigated. It was found that the prepared compounds decreased the growth of Staphylococcus aureus, Escherichia coli, Candida albicans, Rhizopus oryzae and Microsporum gypseum, respectively. The most resistant to all tested compounds was probiotic strain of Lactobacillus plantarum. The presence of zinc and ligands in the prepared compounds increased the inhibitory effect compared to sodium salt of prepared compounds and free ligands.     

A kinetic investigation of reaction of [Os(N)(CH2SiMe3)4][NBun4] with methyl iodide

A high oxidation state alkylnitridoosmium complex, [Os(N)(CH₂SiMe₃)₄][NBuⁿ₄] acts as a nucleophile in reactions with alkyl halides. Alkylimido complexes, Os(NR)(CH₂SiMe₃)₄, are produced. The reaction between [Os(N)(CH₂SiMe₃)₄]⁻ [NBuⁿ₄] and MeI is second order with k₂= 9.5 x 10⁻⁵ sec^t̄1 M⁻¹ at 23°C in CD₂Cl₂ under pseudo first order conditions. The entropy of activation, ΔS^≠, was found to be −10.6 ± 0.5 cal M⁻¹ K⁻¹ and the enthalpy of activation, ΔH^≠, was found to be 19.6 ± 0.2 kcal M⁻¹. The reaction proceeds faster in polar, non-coordinating solvents than in either non-polar solvents or in solvents which can coordinate to the osmium center.     

Diferric oxo-bridged complexes of a polydentate aminopyridyl ligand: synthesis,structure and catalytic reactivity

The catalytic reactivity of a group of diferric oxo-bridged complexes (1–3) of a tetradentate ligand (bpmen = N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)-1,2-diaminoethane) toward alkane hydroxylation has been evaluated. Among the three complexes, the µ-oxo diiron(III) complex [Fe(bpmen)(µ-O)FeCl₃] (1) has been synthesized for the first time. The complex 1 has been characterized by spectroscopic analysis and X-ray crystallography. At room temperature, the µ-oxo diiron(III) complexes 1–3 have been found to be useful catalysts in hydroxylation of alkanes with m-chloroperbenzoic acid as oxidant. [Fe(bpmen)(µ-O)FeCl₃] (1) has been found to be the most active catalyst. Moreover, the catalytic ability of the complexes in the oxidation of alcohols to ketones with hydrogen peroxide at room temperature has also been investigated.     

Solvatochromism and solvation of ternary iron-diimine-cyanide complexes

Summary The solvatochromic behaviour of several complexes [Fe(LL)₂(CN)₂] with LL=Schiff base diimine has been established in a series of non-aqueous solvents, as has that of two analogues containing diazabutadiene ligands. Transfer chemical potentials have been derived from appropriate solubility measurements for several iron(II)-and iron(III)-diimine-cyanide complexes into aqueous methanol, and for [Fe(bipy)₂(CN)₂] into several binary aqueous solvent series. The usefulness of solvatochromic shifts and transfer chemical potentials as indicators of selective solvation is discussed. Kinetics of oxidation of catechol and of 4-t-butyl catechol by [Fe(bipy)(CN)₄]^– in aqueous solution are described.     

The preparation and structure of the tetranuclear ruthenium cluster [Ru4(CO)10(μ2-Cl)2(μ3-OEt)2]

The tetranuclear ruthenium cluster [Ru₄(CO)₁₀Cl₂(OEt)₂] has been prepared in low yield by the reaction of [Ru₃(CO)₁₂] with [N(PPh₃)₂]Cl in refluxing EtOH, followed by oxidation with either [NO][BF₄] or Ag[ClO₄]. A single-crystal X-ray analysis of the complex shows that the four metal atoms adopt a planar geometry with one ruthenium bonded by two μ₂-Cl ligands and two μ₃-OEt ligands to a trinuclear fragment. This complex crystallises in the monoclinic space group I2/c, with a 14.458(3), b 22.073(6), c 15.302(4) Å, β 99.54(2)°, Z = 8; 3113 observed data with F > 3σ(F) were refined by blocked full-matrix least squares to R = 0.031, R_w = 0.034.     

Synthesis, spectral and thermal study on new Fe(III) complexes with N,N-dimethylbiguanide as antibacterial agents

New complexes [FeO(DMBG)]₂ and [Fe(DMBG)₂]Cl·0.5H₂O (HDMBG: N,N-dimethylbiguanide) have been synthesized and characterized by microanalytical, IR and UV–Vis data. Electronic spectra of the complexes are characteristic for a tetrahedral stereochemistry, whilst the modifications in the IR spectra indicate the presence of the DMBG anion as chelate. The thermal decomposition investigated in air by thermal analysis confirmed the proposed formulas for the complexes and provided information concerning the modifications during heating and also the thermodynamic effects accompanying them. The thermal transformations are complex, according to TG and DTG curves including dehydration, hydrochloric acid elimination, oxidative degradation and condensation of –C=N– unit. The final product of decomposition was iron (III) oxide as powder XRD indicates. Complexes were screened for their antimicrobial properties against Gram-positive, Gram-negative bacterial, as well as fungal pathogenic strains. The results indicate that Fe(III) complexes exhibit an improved antibacterial activity against S. aureus and E. coli strains in comparison with free biguanide. The Fe(III) complexes also inhibit the ability of S. aureus, B. subtilis, P. aeruginosa and E. coli strains to colonize the inert substratum, accounting for their possible use as anti-biofilm agents.     

Transition metal complexes with thiosemicarbazide-based ligands

Solvate complexes of UO ₂ ²⁺ andN(1), N(4)-bis(salicylidene)-S-methylisothiosemicarbazone, (H₂Me-L¹), of general formula [UO₂(Me-L¹)S] (S= H₂O, MeOH, EtOH, Py, DMF and DMSO) were synthesized. The methanolic UO ₂ ²⁺ ” adducts of N(1)-benzoylisopropylidene-N(4)-salicylidene-S-alkylisothiosemicarbazone, (H₂R-L²,R=Me, Prⁿ) of general formula [UO₂(R-L²)· MeOH], were also prepared. Thermal decomposition of the complexes was investigated in air and argon. The complexes decompose to α-U₃O₈ in air, while in argon the decomposition is not completed up to 1000 K. The temperature and the mechanism of decomposition of the complexes are a function of the solvent belonging to the inner coordination sphere.     

Oxidation State 10 Exists

In a recent paper, Wang et al. found an iridium‐containing compound with a formal oxidation state of 9. ⁵ This is the highest oxidation state ever found in a stable compound. To learn if this is the highest chemical oxidation state possible, Kohn–Sham density functional theory was used to study various compounds, including PdO₄²⁺, PtO₄²⁺, PtO₃F₂²⁺, PtO₄OH⁺, PtO₅, and PtO₄SH⁺, in which the metal has an oxidation state of 10. It was found that PtO₄²⁺ has a metastable state that is kinetically stable with a barrier height for decomposition of 31 kcal mol^?1 and a calculated lifetime of 0.9 years. All other compounds studied would readily decompose to lower oxidation states.     

Effect of acetonitrile on the catalytic decomposition of hydrogen peroxide by vanadium ions and conjugated oxidation of alkanes

The rate of hydrogen peroxide decomposition in acetonitrile in the presence of a vanadate anion and pyrazine-2-carboxylic acid decreases remarkably when alkane (cyclohexane, n-heptane, isooctane) is added to the reaction solution. The alkane added is oxidized by this system to alkyl hydroperoxide. This is explained by the fact that much more hydrogen peroxide molecules are consumed to acetonitrile oxidation with formation of the final products, which is suppressed considerably by additives of necessary amounts of alkane, than those consumed to the oxidation of cyclohexane to form cyclohexyl hydroperoxide. In an organic solvent, H₂O₂ decomposes in a non-chain radical process.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2231–2234, October, 2004     

Mechanistic studies of oxidation of maltose and lactose by [H2OBr]+ in presence of chloro-complex of Rh(III) as homogeneous catalyst

Kinetic studies in homogeneously Rh(III)-catalyzed oxidation of reducing sugars, i.e. maltose and lactose, by N-bromoacetamide (NBA) in the presence of perchloric acid have been made at 40 °C using mercuric acetate as Br⁻ ion scavenger. The results obtained for the oxidation of both reducing sugars show first-order dependence of the reactions on NBA at its low concentrations, which shifts towards zero-order at its higher concentrations. First-order kinetics in [Rh(III)] and zero-order kinetics in [reducing sugar] were observed. Positive effect of [Cl⁻] was observed in the oxidation of both maltose and lactose. Order of reaction was found to be one and half (1.5) throughout the variation of [H⁺] in the oxidation of both maltose and lactose. An increase in the rate of reaction with the decrease in [Hg(OAc)₂] and [NHA] was observed for both the redox systems. The rate of oxidation is unaffected by the change in ionic strength (μ) of the medium. The main oxidation products of the reactions were identified as formic acid and arabinonic acid in the case of maltose and formic acid, arabinonic acid and lyxonic acid in the case of lactose. A common mechanism for the oxidation of both maltose and lactose, showing the formation of most reactive activated complex, [RhCl₄(H₃O)H₂OBr]⁺, and an unreactive complex, [RhCl₄(H₂O)(H₂OBrHg)]²⁺, has been proposed. Various activation parameters have also been calculated and on the basis of these parameters, a suitable explanation for the reaction mechanism has been given.     

Einfluß des Lösungsmittels auf das Redoxverhalten von Tetrakis(triphenylphosphin)-platin(0), Tetrakis(triphenylphosphin)-palladium(0) und Tetrakis(triphenylphosphin)-nickel(0)

The redox behaviour of tetrakis(triphenylphosphine)-platinum(0) [Pt(TPP)₄], tetrakis(triphenylphosphine)-palladium(0) [Pd(TPP)₄] and tetrakis(triphenylphosphine)-nickel(0) [Ni(TPP)₄] has been studied in N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetonitrile (AN), propanediol carbonate (PDC), N,N-dimethylthioformamide (DMTF) N-methylpyrrolidine-2-thione (NMTP) and nitromethane (NM). The platinum complex was found to undergo irreversible two electron oxidations with partial or complete loss of the ligands in all solvents but nitromethane. The palladium complex was also oxidized to the divalent form in the solvents studied except inPDC andNM where the complex was found to be polarographically inactive; Ni(TTP)₄ was reversibly or almost reversibly oxidized to a movovalent form inDMF, AN andDMTF followed by an irreversible oxidation to a divalent complex. Direct oxidation to the divalent form occurred inDMSO, no oxidation was observable inNMTP andPDC, decomposition took place in nitromethane. The half-wave potentials were recorded versus bisbiphenylchromium iodide (BBCr)I as an internal standard. The influence of the solvents on the redox behaviour and the dissociation of ligands is discussed.

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Mit 1 Abbildung     

Oxidation State 10 Exists

In a recent paper, Wang et al. found an iridium‐containing compound with a formal oxidation state of 9. ⁵ This is the highest oxidation state ever found in a stable compound. To learn if this is the highest chemical oxidation state possible, Kohn–Sham density functional theory was used to study various compounds, including PdO₄²⁺, PtO₄²⁺, PtO₃F₂²⁺, PtO₄OH⁺, PtO₅, and PtO₄SH⁺, in which the metal has an oxidation state of 10. It was found that PtO₄²⁺ has a metastable state that is kinetically stable with a barrier height for decomposition of 31 kcal mol⁻¹ and a calculated lifetime of 0.9 years. All other compounds studied would readily decompose to lower oxidation states.     

[Rh12Sb(CO)27]3-. an example of encapsulation of antimony by a transition metal carbonyl cluster

The reaction of Rh(CO)₂acac with triphenylantimony in the presence of cesium benzoate in tetraethylene glycol/dimethyl ether solution resulted in the selective formation of [Rh₁₂Sb(CO)₂₇]^3- (66% yield) after 3 h of contact time under ≈400 atm of carbon monixide and hydrogen (CO/H₂  1) at 140–160°C. The cluster has been isolated as the [Cs(18-Crown-6)₂]⁺, [(CH₃)₄]⁺, [(C₂H₅)₄N]⁺, (Ph₃P)₂N]⁺ and [PhCH₂N(C₂H₅)₃]⁺ salts. The [(C₂H₅)₄N]₃ [Rh₁₂Sb(CO)₂₇] complex has been characterized via a complete three-dimensional X-ray diffraction study. The complex crystallizes in the space group R$\text{3}$c with a  23.258(13) Å, c  22.811(4) Å, V  10 686 ų and p(calcd.)  2.334 g cm^-3 for mol.wt. 2503.66 and Z  6. Diffraction data were collected with an Enraf-Nonius CAD 4 automated diffractometer using graphite-monochromatized Mo-Kα radiation. The structure was solved by direct methods and refined by difference-Fourier and least-squares techniques. All non-hydrogen atoms have been located and refined: final discrepancy indices are R_f  3.5% and R_wf  4.6% for 3011 reflections. The anion's structure consists of twelve rhodium atoms situated at the corners of a distorted icosahedron with contacts of 2.807(1), 2.861(1), 2.874(1), 2.999(1), 3.017(1) and 3.334(1) Å and rhodium—antimony contacts of 2.712(0) Å. Rhodium—rhodium bond distances of 2.807 and 3.017 Å are in the range usually found for these complexes although a distance of 3.334 Å may be longer than expected from bonding interactions. The sum of the covalent radii of antimony and rhodium, 2.80 Å, is intermediate between the two observed RhSb contacts. The anion cluster structure is that of distorted icosahedron. This polyhedron has previously been found in [B₁₂H₁₂]^2- but not with transition metal clusters. A comparison between the structures of rhodium carbonyl clusters and boranes shows the occurrence of similar structural features. Applications of bonding theories based on the boranes, such as Wade's rules, to rhodium carbonyl clusters shows the extent in which these rules are obeyed.     

New biocatalysts mimicking oxidative hemoproteins: Hemoabzymes

Catalytic antibodies with a metalloporphyrin cofactor or “hemoabzymes”, used as models for hemoproteins like peroxidases and cytochrome P450s, represent a promising route to catalysts tailored for selective oxidation reactions.The first strategy has been to produce anti-porphyrin antibodies, raised against various N-substituted- and meso-carboxyaryl-porphyrins, which led to monoclonal antibodies exhibiting, in the presence of the corresponding iron-porphyrin cofactor, a significant peroxidase activity. We ourselves obtained an artificial hemoprotein by associating a monoclonal antibody, 13G10, and its iron(III)-α,α,α,β-meso-tetrakis(ortho-carboxyphenyl)porphyrin (Fe(ToCPP)) hapten, which exhibited a significant peroxidase activity. Biological studies suggested that in this antibody, a carboxylic acid side chain of the protein participated in the catalysis, but no amino acid residue acting as an axial ligand of the iron was detected. Therefore, to provide the iron atom with an axial ligand, we raised antibodies against microperoxidase 8, a heme octapeptide containing a histidine bound to the iron atom.This strategy was successful, as an antibody–microperoxidase 8 complex (3A3–MP8) led to the best k_cat/K_m ever reported for antibody–porphyrin complexes. The ability of the 3A3–MP8 complex to catalyze the selective oxidation of substrates was studied and it was found able to catalyze the regioselective nitration of aromatics by NO₂⁻/H₂O₂ as well as the stereoselective oxidation of sulfides like thioanisole by H₂O₂.Other strategies based on antibodies have to be developed to obtain more efficient biomimetic systems for cytochrome P450s. A first one could involve the modification of anti-substrate antibodies by covalent linkage of an iron(III)-porphyrin close to the binding site of the substrate, to obtain an artificial hemoprotein able to catalyze its regioselective oxidation.     

Thermoanalytical, spectral and biological study of 4-bromobenzoatozinc(II) complexes containing bioactive organic ligands

New zinc(II) 4-bromobenzoate complex compounds with general formula [Zn(4-BrC₆H₄COO)₂L₂]·xH₂O (where L?=?urea, nicotinamide, phenazone or thiourea, x?=?0?C2) were prepared and characterized by elemental analysis, IR spectroscopy and thermal analysis. The thermal decomposition of hydrated compounds started with dehydration process. During the thermal decomposition, the neutral organic ligand, bis(4-bromophenyl)methanone and carbon dioxide were evolved. The solid intermediates and volatile products of thermal decomposition were proved by IR spectroscopy and mass spectrometry. The final solid product of the thermal decomposition heated up to 800?°C was zinc oxide, which was confirmed by X-ray powder diffractometry. Antimicrobial activity of the prepared compounds was tested against various strains of bacteria, yeasts and filamentous fungi (E. coli, S. aureus, C. albicans, R. oryzae, A. alternata and M. gypseum). It was found that bacterium S. aureus and fungi A. alternata are the most sensitive to the studied compounds.