Influence of solvent composition on the kinetics of cyclooctene epoxidation by hydrogen peroxide catalyzed by iron(III) [tetrakis(pentafluorophenyl)] porphyrin chloride [(F20TPP)FeCl

The epoxidation of cyclooctene catalyzed by iron(III) [tetrakis(pentafluorophenyl)] porphyrin chloride [(F20TPP)FeCl] was investigated in alcohol/acetonitrile solutions in order to determine the effects of the alcohol composition on the reaction kinetics. It was observed that alcohol composition affects both the observed rate of hydrogen peroxide consumption (the limiting reagent) and the selectivity of hydrogen peroxide utilization to form cyclooctene epoxide. The catalytically active species are formed only in alcohol-containing solvents as a consequence of (F(20)TPP)FeCl dissociation into [(F20TPP)Fe(ROH)]+ cations and Cl- anions. The observed reaction kinetics are analyzed in terms of a proposed mechanism for the epoxidation of the olefin and the decomposition of H2O2. The first step in this scheme is the reversible coordination of H2O2 to [(F20TPP)Fe(ROH)]+. The O-O bond of the coordinated H2O2 then undergoes either homolytic or heterolytic cleavage. The rate of homolytic cleavage is found to be independent of alcohol composition, whereas the rate of heterolytic cleavage increases with alcohol acidity. Heterolytic cleavage is envisioned to form iron(IV) pi-radical cations, whereas homolytic cleavage forms iron(IV) hydroxo cations. The iron(IV) radical cations are active for olefin epoxidation, whereas the iron(IV) cations catalyze the decomposition of H2O2. Reaction of iron(IV) pi-radical cations with H2O2 to form iron(IV) hydroxo cations is also included in the mechanism, a process that is favored by alcohols with a high charge density on the O atoms. The proposed mechanism describes successfully the effects of H2O2, cyclooctene, and porphyrin concentrations, as well as the effects of alcohol concentration.     

A study of the mechanism and kinetics of cyclooctene epoxidation catalyzed by iron(III) tetrakispentafluorophenyl porphyrin

A study has been conducted of the mechanism and kinetics of cyclooctene epoxidation by hydrogen peroxide catalyzed by iron(III) tetrakispentafluorophenyl [F(20)TPPFe(III)] porphyrin. The formation of cyclooctene oxide, the only product, was determined by gas chromatography, and the consumption of hydrogen peroxide was determined by (1)H NMR. UV-visible spectroscopy was used to identify the state of the porphyrin as a function of solvent composition and reaction conditions and to follow the kinetics of porphyrin degradation. F(20)TPPFe(III) was found to be inactive in the chloride-ligated form, but became active when the chloride ligand was replaced by a methoxide ligand. The methoxide-ligated form of F(20)TPPFe(III) reacts with hydrogen peroxide to form an iron(III) hydroperoxide species, which then undergoes both heterolytic and homolytic cleavage to form iron(IV) pi-radical cations and iron(IV) oxo species, respectively. The iron(IV) pi-radical cations are responsible for the epoxidation of cyclooctene, whereas the iron(IV) oxo species are responsible for hydrogen peroxide decomposition. The kinetics of cyclooctene epoxidation and hydrogen peroxide decomposition developed from the proposed mechanism describe the experimentally observed kinetics accurately. The rate parameters derived from a fit of the model to the experimental data are consistent with previous estimates of the magnitude of these parameters.     

Synthesis of sulfoxides by the hydrogen peroxide induced oxidation of sulfides catalyzed by iron tetrakis(pentafluorophenyl)porphyrin: scope and chemoselectivity

The oxidation of sulfides with H(2)O(2) catalyzed by iron tetrakis(pentafluorophenyl)porphyrin in EtOH is an efficient and chemoselective process. With a catalyst concentration 0.03-0.09% of that of the substrate, sulfoxides are obtained with yields generally around 90-95% of isolated product. With vinyl and allyl sulfides, no epoxidation is observed. With a catalyst concentration between 0.09% and 0.25% of that of the substrate, sulfones are obtained in almost quantitative yield and with the same high chemoselectivity observed in the synthesis of sulfoxides.     

Effects of methanol on the thermodynamics of iron(III) [tetrakis(pentafluorophenyl)]porphyrin chloride dissociation and the creation of catalytically active species for the epoxidation of cyclooctene

In a previous study, the authors showed that iron(III) [tetrakis(pentafluorophenyl)]porphyrin chloride [(F20TPP)FeCl] is catalytically inactive for cyclooctene epoxidation by hydrogen peroxide in acetonitrile but is catalytically active if the solvent contains methanol. It was suggested that the precursor to the active species is (F20TPP)Fe(OCH3) in methanol-containing solvents. The present study was aimed at evaluating this hypothesis. (F20TPP)Fe(OCH3) was synthesized and characterized by 1H NMR but was found to be inactive in both acetonitrile and methanol. Further investigation of the interactions of (F20TPP)FeCl with methanol in acetonitrile/methanol mixtures was then carried out using NMR. Two species, characterized by 1H NMR resonances at 82 and 65 ppm, were observed. The first resonance is attributed to the beta-pyrrole protons on molecularly dissolved (F20TPP)FeCl, whereas the second is attributed to beta-pyrrole protons of [(F20TPP)Fe]+ cations that are stabilized by coordination with a molecule of methanol, viz., [(F20TPP)Fe(CH3OH)]+. The relative concentration of [(F20TPP)Fe(CH3OH)]+ increases as the fraction of methanol in the solvent increases, suggesting that methanol facilitates the dissociation of (F20TPP)FeCl into cations and anions. A thermodynamic model of the dissociation is proposed and found to describe successfully the experimental observation over a range of solvent compositions, porphyrin concentrations, and temperatures. UV-visible spectroscopy was also used to validate the developed model. In addition, the observed rate constant for cyclooctene epoxidation was found to be proportional to the concentration of [(F20TPP)Fe(CH3OH)]+ calculated using the thermodynamic model, suggesting that this intermediate is a precursor to the species that catalyzes olefin epoxidation. The catalytic activity of [(F20TPP)Fe(CH3OH)]+ was further confirmed through experiments in which (F20TPP)Fe(OCH3) dissolved in methanol was reacted with HCl(aq). This reaction produced a product with an NMR peak at 65 ppm attributable to [(F20TPP)Fe(CH3OH)]+, and this mixture was found to have activity for cyclooctene epoxidation similar to that of (F20TPP)FeCl dissolved in methanol.     

Theoretical study of solvent effects on the thermodynamics of iron(III) [tetrakis(pentafluorophenyl)]porphyrin chloride dissociation

A quasichemical method that combines ab initio treatment of explicit solvent with dielectric continuum models has been used to study the origin of a strong effect of methanol on the extent of iron(III) [tetrakis(pentafluorophenyl)]porphyrin chloride dissociation in acetonitrile-methanol solutions. It is shown that the dissociation is energetically more favorable in methanol than in acetonitrile primarily because of the strong specific interactions between the chloride anion and the solvent methanol molecules in its first solvation shell. These interactions are weaker in acetonitrile. The final estimate for the difference in the dissociation free energies in methanol and acetonitrile is -23 kJ/mol, in a good agreement with the experimental value of -21 kJ/mol. Energy decomposition analysis of chloride-solvent interactions suggests that stronger chloride-methanol binding is a result of the contribution of charge delocalization effects to the chloride-methanol interactions.     

Asymmetric epoxidation of terminal alkenes with hydrogen peroxide catalyzed by pentafluorophenyl PtII complexes

Easily accessible chiral PtII complexes 1 allow highly enantioselective and completely regioselective asymmetric epoxidation of terminal alkenes with hydrogen peroxide     

Efficient solvent-free iron (III) catalyzed oxidation of alcohols by hydrogen peroxide

Selective oxidation of secondary and benzylic alcohols was efficiently accomplished by H₂O₂ under solvent-free condition catalyzed by FeBr₃. Secondary alcohols are selectively oxidized even in the presence of primary ones. This method is high yielding, safe and operationally simple.     

Efficient microwave-assisted synthesis of amine-substituted tetrakis(pentafluorophenyl)porphyrin

We report an efficient and rapid means for the synthesis of tetrakis(pentafluorophenyl)porphyrin (TPPF(20)) derivatives by microwave irradiation in an environmentally acceptable solvent. The selective displacement of the para-fluorine groups in TPPF(20) by primary amines occurs in yields between 70 and 95%. This method demonstrates that TPPF(20) is an ideal platform for the rapid formation of porphyrin conjugates for therapeutic, catalytic, and other applications. [reaction: see text]     

Efficient epoxidation reaction of terminal olefins with hydrogen peroxide catalyzed by an iron (II) complex

A highly active iron (II) complex that catalyzed epoxidation of terminal olefins with hydrogen peroxide was described. The catalytic system displayed excellent catalytic ability for the selective oxidation of terminal olefins to epoxides with high selectivity (up to 97.8%) in CH₃CN at 25?°C. The catalytic activity of three similarly structural iron (II) complexes was comparatively studied. The effect of various auxiliary ligands on epoxidation was investigated in detail.     

Epoxidation of alkenes with hydrogen peroxide catalyzed by iron(III) porphyrins in ionic liquids

An efficient procedure is described for catalyst recycling and easy product isolation in alkene epoxidation with hydrogen peroxide catalyzed by water-soluble iron(III) porphyrins in environmentally benign and ambient temperature ionic liquids.     

The decomposition kinetics of hydrogen peroxide catalyzed by diethylenetriaminepentaacetatoiron(III) complex

The rate of reaction of (Fe(DTPA)) with H₂O₂ was investigated at various temperatures. The observed rate law is given by the expression. The rate constants and the related thermodynamic parameters are calculated. Substitution controlled mechanisms are suggested to account for the formation of the violet peroxy intermediate. The results are compared with previously data for Fe EDTA complex.     

Hangman effect on hydrogen peroxide dismutation by Fe(III) corroles

Hangman Fe(III) corroles catalyse H(2)O(2) disproportionation at a faster rate and display a more pronounced hangman effect than their one electron oxidized analogues owing to their ability to bypass high energy intermediates by redox-leveling derived from the use of the corrole as a non-innocent ligand.     

Kinetics and mechanisms of the catalyzed decomposition of hydrogen peroxide by ethylenebis(oxyethylenedinitrilo)tetracetate complex of iron(III)

The rate of decomposition of H₂O₂ in the presence of Fe(III)-y complex (y is ethylenebis(oxyethylenedinitrilo)tetraacetic acid (EGTA) anion) was investigated under variable conditions of pH and temperature, various water-miscible solvents, and different concentrations of H₂O₂, [Fe-y]⁻, and acetate ions. The following rate law holds: Rate = (k₁K₃K₄/[H⁺]) [Fe-y(OH)]²⁻ [H₂O₂] at pH less than 9.80, and Rate = (k₂K₅[H⁺]/K₃) [Fe-y(OH)₂]³⁻[OOH]⁻ at pH above 9.80. The values of k₁K₄and k₂K₅ at 25 °C were found to be 1523 and 0.747 M⁻¹ S⁻¹, respectively. Activation enthalpy and activation entropy for this reaction were determined from Arrhenius plots and found to be ΔH^* = 34.38 K J mol⁻¹ and ΔS^* = −167.2 J K⁻¹ mol⁻¹.     

Olefin epoxidation with bis(trimethylsilyl) peroxide catalyzed by inorganic oxorhenium derivatives. Controlled release of hydrogen peroxide.

The replacement of organometallic rhenium species (e.g., CH(3)ReO(3)) by less expensive and more readily available inorganic rhenium oxides (e.g., Re(2)O(7), ReO(3)(OH), and ReO(3)) can be accomplished using bis(trimethylsilyl) peroxide (BTSP) as oxidant in place of aqueous H(2)O(2). Using a catalytic amount of a proton source, controlled release of hydrogen peroxide helps preserve sensitive peroxorhenium species and enables catalytic turnover to take place. Systematic investigation of the oxorhenium catalyst precursors, substrate scope, and effects of various additives on olefin epoxidation with BTSP are reported in this contribution.     

Oxidation of aromatic monoterpenes with hydrogen peroxide catalysed by Mn(III) porphyrin complexes

The oxidation of carvacrol 1, thymol 2 and p-cymene 3 with hydrogen peroxide catalysed by Mn(III) porphyrins is reported. The oxidation of 1 and 2 selectively originates thymoquinone 6. From the oxidation of p-cymene 3, the isolated major products 7–10, were formed from the oxidation of positions 7 and 8 of the substrate, although minor amounts of thymoquinone 6 were also formed. The efficiency and selectivity of the catalytic systems and the structural characterisation of the products obtained will be discussed.     

Pre-steady state reactivity of 5,10,15,20-tetrakis(pentafluorophenyl)-21H,23H-porphyrin iron(III) chloride with hydrogen peroxide

A stopped-flow study has shown that tetrakis(pentafluoro-phenyl)porphyrin iron(III) chloride reacts rapidly (<3 ms) with hydrogen peroxide to form a Fe(III)-H(2)O(2) complex where log K = 2.39. This subsequently undergoes rapid intramolecular conversion (k = 4.4 s(-1)) to an iron(IV) intermediate, which in turn reacts with hydrogen peroxide (k' = 54.3 M(-1) s(-1)) to reform the original Fe(III)-H(2)O(2) complex.     

Inclusion complexes of Fe(III) tetrakis(4-sulfonatophenyl)porphyrin with cyclodextrins in aqueous solutions

In aqueous solutions, inclusion complexation of Fe(III) tetrakis(4-sulfonatophenyl)porphyrin (FeTSPP) with alpha-cyclodextrin (alpha-CD), beta-CD, gamma-CD, and heptakis(2,3,6-tri-O-methyl)-beta-CD (TM-beta-CD) has been examined by means of absorption and induced circular dichroism spectroscopy. FeTSPP has been found to form inclusion complexes with beta-CD, gamma-CD, and TM-beta-CD in pH 3.2 buffers. At pH 10.1, where FeTSPP self-associates to form an oxo-bridged dimer, FeTSPP also forms inclusion complexes with alpha-CD, beta-CD, gamma-CD, and TM-beta-CD. The stoichiometries of the CD-FeTSPP inclusion complexes are 1:1, except for TM-beta-CD in pH 10.1 buffers where its 1:1 inclusion complex associates with TM-beta-CD to form a 2:1 inclusion complex at high TM-beta-CD concentrations. Equilibrium constants of FeTSPP for the formation of the 1:1 inclusion complexes have been evaluated for beta-CD, gamma-CD, and TM-beta-CD. Induced circular dichroism spectra of FeTSPP in alpha-CD and beta-CD solutions exhibit a signal pattern (a negative sign) that is different from those in acidic and basic solutions containing gamma-CD and that in basic solution containing TM-beta-CD, suggesting different inclusion modes towards FeTSPP.     

Theoretical study of photoinduced epoxidation of olefins catalyzed by ruthenium porphyrin

Epoxidation of olefin by [Ru(TMP)(CO)(O)](-) (TMP = tetramesitylporphine), which is a key step of the photocatalyzed epoxidation of olefin by [Ru(TMP)(CO)], is studied mainly with the density functional theory (DFT) method, where [Ru(Por)(CO)] is employed as a model complex (Por = unsubstituted porphyrin). The CASSCF method was also used to investigate the electronic structure of important species in the catalytic cycle. In all of the ruthenium porphyrin species involved in the catalytic cycle, the weight of the main configuration of the CASSCF wave function is larger than 85%, suggesting that the static correlation is not very large. Also, unrestricted-DFT-calculated natural orbitals are essentially the same as CASSCF-calculated ones, here. On the basis of these results, we employed the DFT method in this work. Present computational results show characteristic features of this reaction, as follows: (i) The epoxidation reaction occurs via carboradical-type transition state. Neither carbocation-type nor concerted oxene-insertion-type character is observed in the transition state. (ii) Electron and spin populations transfer from the olefin moiety to the porphyrin ring in the step of the C-O bond formation. (iii) Electron and spin populations of the olefin and porphyrin moieties considerably change around the transition state. (iv) The atomic and spin populations of Ru change little in the reaction, indicating that the Ru center keeps the +II oxidation state in the whole catalytic cycle. (v) The stability of the olefin adduct [Ru(Por)(CO)(O)(olefin)](-) considerably depends on the kind of olefin, such as ethylene, n-hexene, and styrene. In particular, styrene forms a stable olefin adduct. And, (vi) interestingly, the difference in the activation barrier among these olefins is small in the quantitative level (within 5 kcal/mol), indicating that this catalyst can be applied to various substrates. This is because the stabilities and electronic structures of both the olefin adduct and the transition state are similarly influenced by the substituent of olefin.     

Kinetic study of hydrogen peroxide reaction with hydroxonitrilotri(methylenephosphonato)iron(III) complex

The decomposition of hydrogen peroxide in the presence of hydroxonitrilotri(methylenephosphonato)iron(III), [Fe(NTMP)(OH)^4–], was studied in nitrate media (=0.10–0.26 M) over the 0.2–0.5 mM concentration range for the iron complex and the temperature range 26–40°C. The rate law;