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Enhanced Catalytic Activity and Unexpected Products from the Oxidation of Cyclohexene by Organic Nanoparticles of 5,10,15,20-Tetrakis-(2,3,4,5,6-pentafluorophenyl)porphyrinatoiron(III) in Water by Using O 2
Chemistry - A European Journal
Abstract
The catalytic oxidation of alkenes by most iron porphyrins using a variety of oxygen sources, but generally not dioxygen, yields the epoxide with minor quantities of other products. The turnover numbers for these catalysts are modest, ranging from a few hundred to a few thousand depending on the porphyrin structure, axial ligands, and other reaction conditions. Halogenation of substituents increases the activity of the metalloporphyrin catalyst and/or makes it more robust to oxidative degradation. Oxidation of cyclohexene by 5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorophenyl)porphyrinato iron(III), ([Fe(III)(tppf(20))]) and H(2)O(2) is typical of the latter: the epoxide is 99 % of the product and turnover numbers are about 350.1-4 Herein, we report that dynamic organic nanoparticles (ONPs) of [Fe(III)(tppf(20))] with a diameter of 10 nm, formed by host-guest solvent methods, catalytically oxidize cyclohexene with O(2) to yield only 2-cyclohexene-1-one and 2-cyclohexene-1-ol with approximately 10-fold greater turnover numbers compared to the non-aggregated metalloporphyrin in acetonitrile/methanol. These ONPs facilitate a greener reaction because the reaction solvent is 89 % water and O(2) is the oxidant in place of synthetic oxygen sources. This reactivity is unexpected because the metalloporphyrins are in close proximity and oxidative degradation of the catalyst should be enhanced, thus causing a significant decrease in catalytic turnovers. The allylic products suggest a different oxidative mechanism compared to that of the solvated metalloporphyrins. These results illustrate the unique properties of some ONPs relative to the component molecules or those attached to supports.
... [1,2] As such, it is useful across the board, from bulk chemicals anda grochemicals [3,4] all the way to fine chemicals and fragrances. [5][6][7] In theory,a llylic oxidation is as traightforward exothermic reaction. It requires only O 2 ,afree, eco-friendly and widely available reagent. ...
... Notably,t he differencei nt he surface area between the carbon and the g-alumina was corrected for by increasing the catalyst amount accordingly.T ob oost the number of free radicals at the start of the reaction, we added H 2 O 2 (13 mol % relative to the substrate, entry 3). [5,7] H 2 O 2 can decompose into water and oxygen under these reactionc onditions. The water With coppero xide, however,t he addition of H 2 O 2 or an increase of the reaction temperature affected both the conversion and the selectivity (entries 7a nd 8). ...
We study the allylic oxidation of cyclohexene with dioxygen under mild conditions in the presence of transition-metal catalysts. The catalysts are comprised of nanometric metal oxide particles supported on porous nitrogen-doped carbons (M/N:C, where M = V, Cr, Fe, Co, Ni, Cu, Nb, Mo, and W). Most of these metal oxides give only moderate conversions, whereof the majority of the products are over-oxidation products. Co/N:C and Cu/N:C, however, give 70-80% conversion and 40-50% selectivity to the ketone product, cyclohexene-2-one. Control experiments using free-radical scanvengers shows that the oxidation follows the expected free-radical pathway in almost all cases. Surprisingly, the catalytic cycle in the presence of Cu/N:C does not involve free-radical species in solution. Optimisation of this catalyst gives >85% conversion with >60% selectivity to the allylic ketone, at 70 °C and 10 bar oxygen pressure. Scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction studies show that the active particles have a cupric oxide/cuprous oxide core/shell structure, with a correspondingly high TOF of ca. 1500 h-1. We attribute the high performance of this Cu/N:C catalyst to a facile surface reaction between adsorbed cyclohexenyl hydroperoxide molecules and activated oxygen species.
... A related issue was recently exploited by Liu et al, who demonstrated evolution of porphyrin globular nanostructures into nanofibers. [35] The different morphologies of the aggregates are the consequence of the progressive change of mechanism, driven by changing concentration. ...
Solvent-driven aggregation of a series of porphyrin derivatives was studied by UV/Vis and circular dichroism spectroscopy. The porphyrins are characterised by the presence in the meso positions of steroidal moieties further conjugated with glucosyl groups. The presence of these groups makes the investigated macrocycles amphiphilic and soluble in aqueous solvent, namely, dimethyl acetamide/water. Aggregation of the macrocycles is triggered by a change in bulk solvent composition leading to formation of large architectures that express supramolecular chirality, steered by the presence of the stereogenic centres on the periphery of the macrocycles. The aggregation behaviour and chiroptical features of the aggregates are strongly dependent on the number of moieties decorating the periphery of the porphyrin framework. In particular, experimental evidence indicates that the structure of the steroid linker dictates the overall chirality of the supramolecular architectures. Moreover, the porphyrin concentration strongly affects the aggregation mechanism and the CD intensities of the spectra. Notably, AFM investigations reveal strong differences in aggregate morphology that are dependent on the nature of the appended functional groups, and closely in line with the changes in aggregation mechanism. The suprastructures formed at lower concentration show a network of long fibrous structures spanning over tens of micrometres, whereas the aggregates formed at higher concentration have smaller rod-shaped structures that can be recognised as the result of coalescence of smaller globular structures. The fully steroid substituted derivative forms globular structures over the whole concentration range explored. Finally, a rationale for the aggregation phenomena was given by semiempirical calculations at the PM6 level.
It is widely recognised that renewable hydrogen will play a key role in our future energy mix. One approach is to use photocatalytic water-splitting devices for sustainable hydrogen generation. For these devices to function effectively, materials that can capture sunlight are essential. In this review porphyrins and their suitability as photosensitisers and/or proton reduction photocatalysts are discussed, both within homogeneous, heterogeneous and photo-electrochemical environments. In particular, the various parameters that can be varied will be compared, and also the difficulty in accurate comparisons, as there is no standard reporting approach. The photochemistry is further complemented by a systematic review of the use of electrochemistry in designing photocatalytic porphyrin based systems for hydrogen evolution.
Over the last three decades, synthetic supramolecular systems involving porphyrins and related macrocycles have been well explored for numerous applications ranging from catalyst to biomedical to sensors. Advances in synthetic strategies for various porphyrinoids, the ability to functionalize them with many recognition groups, and their rich supramolecular chemistry make these compounds superior platforms for the development of advanced materials, therapeutics, and more. In addition, the distinctive physicochemical properties of these macrocycles can be further tuned by appending exocyclic motifs or chelating metal ions in their core.
In order to make full use of the impact of internal and external factors on the performance of title catalyst for ethyl benzene oxidation, the key internal influencing factors on the catalytic performance were modulated by coordinating and grafting manganese porphyrin to mesoporous and macroporous chitosan, and the important external factors (i.e. oxidation reaction conditions) were optimized using Response Surface Methodology. Under the Response Surface Methodology optimized oxidation reaction conditions (176.56 °C, 0.59 MPa, and 0.25 mg amount of manganese porphyrin), the catalyst could be used at least five times. The ethyl benzene conversion, catalyst turnover numbers, and yields reached up to 51.2%, 4.37 × 106 and 36.4% in average, respectively. Compared with the other optimized oxidation reaction conditions, the corresponding values increased 17%, 26% and 53%. Relative to the manganese porphyrin, the catalytic performance and efficiency of the immobilized catalyst had notably increased.
The utilization of metalloporphyrins as bioinspired oxidation catalysts is an evolutionary topic of research. From the understanding of the cytochrome P-450 mechanism of action, chemists have successfully mimicked several types of oxidation reactions using metalloporphyrins as catalysts. At first, homogeneous systems presented the most amenable strategy for oxidizing a vast array of substrates; however, current environmental concerns have directed research in this field for the design, synthesis and application of heterogeneous catalysts, as well as avoiding the use of highly pollutant co-oxidants and/or co-catalysts. Herein, we review the last decade (from 2008) concerning the sole use of source molecular oxygen as environmentally benign oxidant, in oxidation reactions catalyzed by bioinspired metalloporphyrin analogues. We did not intend to create a comprehensive review; instead we highlight the most important and illustrative examples for this period. We emphasize the application of such catalysts on the oxidation reactions of many relevant substrates using homogeneous and heterogeneous metalloporphyrin based catalysts, mostly using inorganic supports for more accessible reutilization protocols.
Novel non-symmetric third-generation manganese metalloporphyrins, chlorido(5-(4-nitrophenyl)-10,15,20-triphenyl-2,3,7,8,12,13,17,18 octobromoporphyrinate)manganese(III) (MnBr8P1) and the mixture of isomers chlorido(5,10-(4-nitrophenyl)-15,20-diphenyl-2,3,7,8,12,13,17,18-octabromoporphyrinate)manganese(III) and chlorido(5,15-(4-nitrophenyl)-10,20-diphenyl-2,3,7,8,12,13,17,18-octabromoporphyrinate)manganese(III) (cis/trans-MnBr8P2) were obtained from their second-generation analogues (MnP1 and cis/trans-MnP2). These four catalysts were used in cyclohexane oxidation reactions with iodosylbenzene (PhIO) or iodobenzene diacetate (PhI(OAc)2) in the presence or absence of solvent (CH2Cl2). Cyclohexanol (Cy-ol) and cyclohexanone (Cy-one) were the sole reaction products. Regardless of the system, third-generation catalysts MnBr8P1 and cis/trans-MnBr8P2 performed better than second-generation catalysts (MnP1 and cis/trans-MnP2, respectively). In solvent systems, cis/trans-MnBr8P2 afforded a greater total yield (%Cy-ol + %Cy-one) than systems using MnBr8P1, with an increase from 80 to 89% in PhIO and from 47 to 57% in PhI(OAc)2. The systems without solvent, showed to be viable and presented significant yields with PhIO as oxidant, with total yield of 30% for MnBr 8 P1, and 55% for cis/trans-MnBr8P2. Additionally, in systems with third-generation catalysts without solvent, selectivity was close to 100% for Cy-ol.
The results of theoretical and experimental studies of the structure and properties of poly-meric carbon nitrides are reviewed. Various routes of the synthesis of these compounds using nitrogen-rich precursors, viz., cyanamide, dicyandiamide, carbamide, melamine, etc., are described. Particular attention is paid to the catalytic properties of graphite-like carbon nitrides and methods of their texture and chemical modification. The main trends for the synthesis of meso- and nanostructured materials based on graphite-like carbon nitrides are considered. Prospects of their practical application as efficient photo-, electro-, and heterogeneous metal-free catalysts are discussed.
Self-organized organic nanoporphyrins were synthesized in the presence of bio silver nanoparticles (AgNPs) using extracted Sesbania sesban plant (ESS). For this novel nanohybrid, [(Ag/MnP)NPs], with the size of 15 nm, manganese (III) meso-tetraphenylporphyrin complex (MnP) was used along with host-guest solvent methods. This nanobiomaterial was characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), FT-IR, X-ray photoelectron spectroscopy (XPS) and UV-vis spectroscopy. The effects of MnP amount, AgNPs amount, and presence of ESS on the morphology and size of nanohybrid were investigated by SEM. The application of it was evaluated as a heterogeneous catalyst for oxidation of alcohols by tetra-n-butylammonium peroxomonosulfate (TB) as an oxidant. Catalysts could be easily reused without noticeable loss of activity and the oxidant's by-product could also be recycled. According to the turnover numbers, the high stability and activity of (Ag/MnP)NPs were observed in the absence of ESS to compare to those synthesized in the presence of ESS.
The novel iridium-pentafluorophenyl porphyrin complex (TPFPPIrCl(CO)) was successfully synthesized by chemical reaction with the iridium (I) metal precursor [Ir(COD)Cl]2. The final complex was identified linked to the axial Cl and CO ligands by UV-Visible, ¹H, ¹³C NMR spectroscopy as well the ¹H/¹³C correlated techniques and by mass spectrometry.
Herein, we introduce a new strategy towards the cyclohexene oxidation reaction, which is driven by molecular oxygen with a cobalt(ii)/amine acid complex as the catalyst without any solvents. The as-prepared products include cyclohexene oxide, 2-cyclohexene-1-ol and 2-cyclohexene-1-one. Under optimized conditions, the oxidation of cyclohexene with molecular oxygen yields a conversion rate of 82.5%. Notably, the catalytic oxidation system has the advantages of being clean, safe and operationally simple. Our experiment indicates that the oxidation follows a radical-chain mechanism rather than a catalytic mechanism, which reveals that 2-cyclohexene-1-hydroperoxide could play a key role in the free-radical chain reaction through a complicated but necessary product analysis.
Organic nanoparticles (ONp) of an Fe(III) porphyrin appended with four N-polyethyleneglyco-pyridinium moieties prepared in acetonitrile were deposited onto hydrophilic or hydrophobic Si surfaces. Self-organized by intermolecular interactions, ONp reorganize in response to environmental changes. Mechanisms for the control of nanoparticle morphologies and surface patterning by varying surface energies are discussed.
In the present research meso-tetrakis(4-carboxyphenyl)porphyrinatomanganese(III) acetate (Mn(TCPP)OAc) nanoparticles have been prepared for the first time without any stabilizing agent or supporting matrix under ultrasonic irradiation. Scanning electron microscopy (SEM) was used to characterize and investigate the nanocatalyst. Rapid, efficient, facile and highly selective oxidation of a wide range of olefins by tetra-n-butylammonium hydrogen monopersulfate over the prepared manganese nanocatalyst was investigated. Also oxidation of sulfides and alkanes in the presence of the (Mn(TCPP)OAc) nanoparticles were studied. The catalyst is recovered by filtration and reused at least five times.
A summary of photonic materials based on porphyrinoids from the laboratory of Charles Michael Drain
Porphyrinoids are robust heterocyclic dyes studied extensively for their applications in medicine and as photonic materials because of their tunable photophysical properties, diverse means of modifying the periphery, and the ability to chelate most transition metals. Commercial applications include their use as phthalocyanine dyes in optical discs, porphyrins in photodynamic therapy, and as oxygen sensors. Most applications of these dyes require exocyclic moieties to improve solubility, target diseases, modulate photophysical properties, or direct the self-organization into architectures with desired photonic properties. The synthesis of the porphyrinoid depends on the desired application, but the de novo synthesis often involves several steps, is time consuming, and results in low isolated yields. Thus, the application of core porphyrinoid platforms that can be rapidly and efficiently modified to evaluate new molecular architectures allows researchers to focus on the design concepts rather than the synthesis methods, and opens porphyrinoid chemistry to a broader scientific community. We have focused on several widely available, commercially viable porphyrinoids as platforms: meso-perfluorophenylporphyrin, perfluorophthalocyanine, and meso-perfluorophenylcorrole. The perfluorophenylporphyrin is readily converted to the chlorin, bacteriochlorin, and isobacteriochlorin. Derivatives of all six of these core platforms can be efficiently and controllably made via mild nucleophilic aromatic substitution reactions using primary S, N, and O nucleophiles bearing a wide variety of functional groups. The remaining fluoro groups enhance the photo and oxidative stability of the dyes and can serve as spectroscopic signatures to characterize the compounds or in imaging applications using (19)F NMR. This review provides an overview of the chemistry of fluorinated porphyrinoids that are being used as a platform to create libraries of photo-active compounds for applications in medicine and materials.
The use of glycosylated porphyrins, phthalocyanines, and other porphyrinoids for diagnostics and therapeutics are discussed. Porphyrins and phthalocyanines (Pcs) are the most common and efficient photosensitizers (PSs) used in photodynamic therapy (PDT) due to their absorption in the visible range of the electromagnetic spectrum, long-lived triplet excited state, and efficient phototoxicity toward cancer cells. Several derivatives can be prepared from porphyrins and phthalocyanines because of the stability of the core macrocycle. New methods have been developed to synthesize dihydroporphyrins and tetrahydroporphyrins for diagnostics and therapeutics uses.
One novel porphyrin 5,10,15,20-tetra(4-(4-acetateethyl)phenoxy)phenylporphyrin (H2Pp), and its two corresponding zinc(II) and copper(II) porphyrins (ZnPp, CuPp) is synthesized and characterized by spectroscopic techniques. The single crystal structures of [ZnPp(DMF)]·DMF (1) and [CuPp(DMF)] (2) are also obtained and analyzed. Complex 1 crystallizes in monoclinic system compared to the triclinic system of complex 2, which may due to the influence of solvent DMF molecule in 1. The metal centers have similar coordination environments in the two structures, which are all five-coordinated pyramid geometry with four nitrogen atoms of porphyrin ring from equator and an axial oxygen atom of DMF molecule. 1 and 2 display 3D supramolecular structures constructed by π⋯π interactions of porphyrin rings and C–H⋯O hydrogen bonds. The catalytic activities of 1 and 2 to the ethylbenzene oxidation are examined. The results indicate that both of them exhibit highly selectivity to acetophenone (> 99%) with the conversion of 23% (1) and 76% (2) respectively.
Allylic oxidations of olefins to enones are C-H functionalizations and are valuable organic transformations that permit the synthesis of value-added products from simple precursors. A variety of stoichiometric and catalytic metal-based methods are available for these conversions. In addition, metal-free and biocatalytic protocols are gaining in importance. This review summarizes the available oxidation methods and compares their regio- and chemoselectivities. 1Introduction 2Chromium-Based Oxidation 2.1Stoichiometric Methods 2.2Catalytic Methods 2.3Chromium on Solid Support 3Regio- and Chemoselectivity of Allylic Oxidations 4Other Metal-Based Oxidations 4.1Copper Reagents 4.2Rhodium Reagents 4.3Selenium Reagents 4.4Cobalt Reagents 4.5Ruthenium Reagents 4.6Palladium Reagents 4.7Iron Reagents 4.8Other Metal Reagents 5Metal-Free and Biocatalytic Methods 5.1Metal-Free Methods 5.2Biocatalytic Methods 6Conclusion
Amphiphilic poly[poly(ethylene glycol) methyl ether methacrylate]-b-poly(azidopropyl acrylamide) (PPEGMEMA-b-PAzPA) block copolymers are synthesized via a combination of reversible addition-fragmentation chain transfer (RAFT) polymerization and a reactive ester-amine reaction. The azido-functionalized PPEGMEMA-b-PAzPA block copolymers can self-assemble into polymeric micelles in an aqueous medium and encapsulate hydrophobic alkynyl-containing manganese(III)porphyrin (MnP) within the core domain. The subsequent in situ copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) leads to the formation of PEGylated-MnP nanoparticles (PEG-MnP NPs). The as-synthesized PEG-MnP NPs are explored as a heterogeneous catalyst for oxidation of cyclohexene in water. The effect of various parameters, such as precursor oxidants, substrate to catalyst loading ratio, and presence of a cocatalyst, is investigated to optimize the oxidation conditions. The catalytic activity of PEG-MnP NPs in water is also compared with that of dissolved MnP in organic solvent.
Polymere graphitische Kohlenstoffnitrid-Materialien (vereinfacht g-C3N4), die nur aus C, N und Spuren von H bestehen, sind in den letzten Jahren wieder verstärkt in das Zentrum des Interesses gerückt, wohl auch wegen der Ähnlichkeit zu Graphit. g-C3N4 ist anders als Graphit ein Halbleiter mit mittlerer Bandlücke und damit ein effektiver (Photo)-Katalysator für eine ganze Reihe von Reaktionen. In diesem Aufsatz beschreiben wir die “Polymerchemie” des synthetischen Aufbaus, wie die Bandlagen und die Bandlücke durch Copolymerisation und Dotierung verändert werden können und wie Änderungen der Festkörpertextur die Effektivität dieses heterogenen Organokatalysators verbessern können. g-C3N4 und seine Modifikationen zeigen eine sehr hohe thermische und chemische Stabilität und katalysieren eine ganze Reihe von “Traumreaktionen”, wie die photochemische Spaltung von Wasser, milde und selektive Oxidationsreaktionen, oder – als coaktiver Katalysatorträger – superschnelle Hydrierungen. Da Kohlenstoffnitrid metallfrei ist, toleriert es funktionelle Gruppen und ist daher für Vielzweckanwendungen in der Umwandlung von Biomasse und in der nachhaltigen Chemie geeignet.
Porphyrins are heterocyclic macrocycles that are extensively studied as functional materials and components of devices in several fields of science because of their unique and tunable characteristics. The periphery of the ring can be functionalized with a variety of substituents that modulate both the photophysical and the materials properties. Because of their exceptional and tunable opto-electronic properties, porphyrins have been studied for energy related applications ranging from energy storage to materials for organic photovoltaics and to catalysis. Substitution with perfluoro-Alkane moieties and perfluoro-phenyl groups improve their supramolecular self-organizing properties as well as the robustness of porphyrinic materials. The preparation of highly fluorinated porphyrins and formation of thin films for studies of their photonic properties are discussed. The fabrication of stable nanoparticles of iron perfluorophenylporphyrin, the derivative with para fluorous alkanes, and the performance of these systems as catalysts is introduced. For all of these materials, the presence of fluorines stabilizes the nanocomposites and increases their resistance towards oxidation.
Organic nanoparticles of metalloporphyrins can be a versatile catalyst for the selective oxidation of alkenes and other hydrocarbons. The catalytic activity of the metalloporphyrin depends on the nature of the central metal atom, peripheral groups, and the architecture of the porphyrin macrocycle. Herein, we report the catalytic activity of organic nanoparticles of 5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorophenyl)porphyrinato manganese(III), Mn(III)TPPF20, for the oxidation of cyclohexene using molecular oxygen as an oxidant in aqueous solvent under ambient conditions. While the solvated metalloporphyrins catalytically oxidize alkenes to the corresponding epoxide with a modest turn-over numbers, ca. 30 nm organic nanoparticles of Mn(III)TPPF20 have enhanced catalytic activity with up to a two-fold greater turn-over number and yields only allylic oxidation products. The activity of organic nanoparticles is slow compared to the solvated metalloporphyrins. These organic nanoparticles catalytic systems facilitate a greener reaction since ca. 89% of the reaction medium is water, molecular oxygen is used in place of man-made oxidants, and the ambient reaction conditions require less energy. This organic nanoparticle catalytic system also avoids using halogenated solvents commonly used in solution phase reactions. The enhanced catalytic activity of these organic nanoparticles is unexpected because the metalloporphyrins in the nanoaggregates are in the close proximity and the turn-over number should diminish by self-oxidative degradation.
The economy of space and materials and the continuously increasing demand for advanced functionalities for diverse technologies requires the development of new synthetic methods. Many nanomaterials have enhanced photophysical and photochemical properties in solutions and/or on surfaces, while others have enhanced chemical properties, compared to the atomic, molecular, or bulk phases. Nanomaterials have a wide range of applications in catalysis, sensors, photonic devices, drug delivery, and as therapeutics for treatment of a variety of diseases. Inorganic nanoparticles are widely studied, but the formation of organic nanomaterials via supramolecular chemistry is more recent, and porphyrinoids are at the forefront of this research because of their optical, chemical, and structural properties. The formation of nanoscaled materials via self-assembly and/or self-organization of molecular subunits is an attractive approach because of reduced energy requirements, simpler molecular subunits, and the material can be adaptive to environmental changes. The presence of biocompatible groups such as peptides, carbohydrates, polyglycols and mixtures of these on the periphery of the porphyrin macrocycle may make nanoparticles suitable for therapeutics. This perspective focuses on responsive, non-crystalline porphyrinoid nanomaterials that are less than about 100 nm in all dimensions and used for catalytic or therapeutic applications.
The experimental conditions (solvent, base, temperature and oxidant) for allylic and benzylic oxidation reactions catalyzed by dirhodium(II)/N-heterocyclic carbene (NHC) complexes were optimized for the first time in this work. The oxidations of cyclohexene and fluorene were used as model reactions. Two optimized experimental conditions for both types of oxidations were found, which resulted in their ketone [aerobic conditions, 40 °C, 1 equiv. tBuOOH (TBHP)] or tert-butyl peroxide derivatives (anaerobic conditions, 25 °C, 2 equiv. TBHP). The dirhodium(II) complexes undergo a single-electron reversible oxidation by cyclic voltammetry in CH2Cl2, which is assigned to the Rh24+/Rh25+ redox couple at an oxidation potential that is lowered upon sequential axial coordination of further ligands to the Rh–Rh centre. The oxidation potential is discussed in terms of the electron-donor character of the NHC ligand, which was shown to act as an effective electron-releaser to the Rh24+ centre, and the electrochemical behaviour is compared to the observed catalytic activity.
A stable s uspension of simple manganese(III) meso -tet-
raphenylporphyrin nanoaggregates was prepared by a host–
guest procedure, in which ethanol and water are used a s
“green” solvents. The organic nanoparticles were studied by
dynamic light scattering ( DLS), AFM, and UV/Vi s and fluo-
rescence s pectroscopy. The results indicate that the nanoag-
gregates have a s pherical morphology with sizes between
15–40 nm. The epoxidation of olefins and oxygenation of s at-
urated hydrocarbons by PhI(OAc) 2 were efficiently enhanced
with excellent selectivity under the i nfluence of simple
Mn(TPP)OAc (TPP = meso-tetraphenylporphyrin) nanopar-
ticles. Enhanced stabilities and activities were achieved with
nanostructured Mn catalysts compared to those of the indi-
vidual counterparts in solution according to turnover num-
bers and UV/Vis studies. The title nanocatalyst facilitates a
greener reaction because the reaction solvent is a water/eth-
anol mixture a nd PhI(OAc) 2 is safe to use. The efficiency of
the oxidation system depends critically upon the steric hin-
drances and electronic structures of both nitrogen donor li-
gands and porphyrin nanoparticles.
Various nanostructures of 5,10,15,20-tetrakis(4-carboxyl phenyl)-porphyrin (H2TCPP) can be easily synthesized by a surfactant-assisted self-assembly (SAS) method at different temperatures. When the DMF solution of porphyrin monomer was injected into cetyltimethylammonium bromide (CTAB) aqueous solution by a syringe, diverse H2TCPP nanostructures dependent on the different temperatures, including hollow nanospheres, solid nanospheres and nanospheres with holes, were successfully obtained. As a result, the suitable concentration of the CTAB aqueous solution used to form nanostructues of porphyrin ranges from 0.15 to 0.2mM. The various morphologies of porphyrin nanostructures were characterized by transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). UV-vis adsorption spectra showed that the micro-/nano-aggregate properties of porphyrin transformed from H-aggretates to J-aggregates during the process of self-assembly of porphyrin at different temperatures. Fluorescence spectra revealed a greater fluorescence quenching of various micro-/nano-aggregatess of porphyrin formed at different temperatures in aqueous solution, compared to the DMF solution of porphyrin monomer.
The synthesis of a porous organic polymer (POP) containing free-base porphyrin subunits has been accomplished by the condensation of a bis(phthalic acid)porphyrin with tetra(4-aminophenyl)methane. Metallation by post-synthesis modification affords microporous materials incorporating either Fe or Mn(porphyrins) that have been shown to be active catalysts for both olefinepoxidation and alkanehydroxylation.
Multifunctional molecules bearing different dyes, such as donor-acceptor systems, synthesized by covalent chemistry have provided a wealth of information on the fundamental nature of electron and energy transfer in organic systems and there is a growing literature on the materials properties of dyes on surfaces. However, in the vast majority of cases the synthetic costs of producing these covalently bound systems prohibit them from deployment in commercially viable devices. Thus, to achieve both the needed multifunctionality and to bring the synthetic costs in line with potential commercialization, supramolecular approaches to the formation of photonic materials can be exploited. This perspective focuses on porphyrinoids as exemplary dyes, but the concepts and design principles extend to other chromophores.
The allyl moiety of 4-allyl-anisol was oxidized in the presence of a Fe(III) porphyrin derivative to the corresponding α,β-unsaturated aldehyde in an initial oxidation step with perfect chemoselectivity. Molecular oxygen was employed as the sole environmental innocuous oxidant. The reaction was performed in an aqueous buffer/CH2Cl2 mixture using the detergent Tween 80 to homogenize the system.
Amphiphilic porphyrin derivatives adsorbed onto silica nanoparticles via noncovalent interactions have been prepared and characterized. The organic-inorganic hybrids have been obtained by simply stirring a nanoparticle suspension into an aqueous solvent mixture of porphyrin aggregates. The systems obtained show good stability in aqueous solvents, at different pH, and also in toluene. Analogous protocol has been applied to the macrocycles in monomeric form, obtaining the corresponding nanoparticle-porphyrin adducts. These systems are of interest for the development of sensors and medicinal application.
Self-organized organic nanoparticles (ONP) are adaptive to the environmental reaction conditions. ONP of fluorous alkyl iron(III) porphyrin catalytically oxidize cyclohexene to the allylic oxidation products. In contrast, the solvated metalloporphyrin yields both allylic oxidation and epoxidation products. The ONP system facilitates a greener reaction because about 89% reaction medium is water, molecular oxygen is used in place of synthetic oxidants, and the ambient reaction conditions used require less energy. The enhanced catalytic activity of these ONP is unexpected because the metalloporphyrins in the nanoaggregates are in the close proximity and the TON should diminish by self-oxidative degradation. The fluorous alkyl chain stabilizes the ONP toward self-oxidative degradation.
Polymeric graphitic carbon nitride materials (for simplicity: g-C(3)N(4)) have attracted much attention in recent years because of their similarity to graphene. They are composed of C, N, and some minor H content only. In contrast to graphenes, g-C(3)N(4) is a medium-bandgap semiconductor and in that role an effective photocatalyst and chemical catalyst for a broad variety of reactions. In this Review, we describe the "polymer chemistry" of this structure, how band positions and bandgap can be varied by doping and copolymerization, and how the organic solid can be textured to make it an effective heterogenous catalyst. g-C(3)N(4) and its modifications have a high thermal and chemical stability and can catalyze a number of "dream reactions", such as photochemical splitting of water, mild and selective oxidation reactions, and--as a coactive catalytic support--superactive hydrogenation reactions. As carbon nitride is metal-free as such, it also tolerates functional groups and is therefore suited for multipurpose applications in biomass conversion and sustainable chemistry.
Controlling the organization of molecular building blocks at the nanometer level is of utmost importance, not only from the viewpoint of scientific curiosity, but also for the development of next-generation organic devices with electrical, optical, chemical, or biological functions. Self-assembly offers great potential for the manufacture of nanoarchitectures (nanostructures and nanopatterns) over large areas by using low-energy and inexpensive spontaneous processes. However, self-assembled structures in 3D media, such as solutions or solids, are not easily incorporated into current device-oriented nanotechnology. The scope of this review is therefore to introduce the expanding methodology for the construction of thin-film-based nanoarchitectures on solid surfaces and to try to address a general concept with emphasis on the availability of dynamic interfaces for the creation and manipulation of nanoarchitectures. In this review, the strategies for the construction of nanostructures, the control and manipulation of nanopatterns, and the application of nanoarchitectures are described; the construction strategies are categorized into three classes: i) π-conjugated molecular assembly in two dimensions, ii) bio-directed molecular assembly on surfaces, and iii) recent thin-film preparation technologies.
The recent surge of interest in metal-catalysed C-H bond functionalisation reactions reflects the importance of such reactions in biomimetic studies and organic synthesis. This critical review focuses on metalloporphyrin-catalysed saturated C-H bond functionalisation reported since the year 2000, including C-O, C-N and C-C bond formation via hydroxylation, amination and carbenoid insertion, respectively, together with a brief description of previous achievements in this area. Among the metalloporphyrin-catalysed reactions highlighted herein are the hydroxylation of steroids, cycloalkanes and benzylic hydrocarbons; intermolecular amination of steroids, cycloalkanes and benzylic or allylic hydrocarbons; intramolecular amination of sulfamate esters and organic azides; intermolecular carbenoid insertion into benzylic, allylic or alkane C-H bonds; and intramolecular carbenoid C-H insertion of tosylhydrazones. These metalloporphyrin-catalysed saturated C-H bond functionalisation reactions feature high regio-, diastereo- or enantioselectivity and/or high product turnover numbers. Mechanistic studies suggest the involvement of metal-oxo, -imido (or nitrene), and -carbene porphyrin complexes in the reactions. The reactivity of such metal-ligand multiple bonded species towards saturated C-H bonds, including mechanistic studies through both experimental and theoretical means, is also discussed (244 references).
Nanoparticles, each consisting of one of the three molecular corrolazine (Cz) compounds, H(3)(TBP(8)Cz), Mn(III)(TBP(8)Cz), and Fe(III)(TBP(8)Cz) (TBP(8)Cz = octakis(4-tert-butylphenyl)corrolazinato), were prepared via a facile mixed-solvent technique. The corrolazine nanoparticles (MCz-NPs) were formed in H(2)O/THF (10:1) in the presence of a small amount of a polyethylene glycol derivative (TEG-ME) added as a stabilizer. This technique allows highly hydrophobic Czs to be "dissolved" in an aqueous environment as nanoparticles, which remain in solution for several months without visible precipitation. The MCz-NPs were characterized by UV-visible spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM) imaging, and shown to be spherical particles from 100-600 nm in diameter with low polydispersity indices (PDI = 0.003-0.261). Particle size is strongly dependent on Cz concentration. The H(3)Cz-NPs were adsorbed on to a modified self-assembled monolayer (SAM) surface and imaged by atomic force microscopy (AFM). Adsorption resulted in disassembly of the larger H(3)Cz-NPs to smaller H(3)Cz-NPs, whereby the resulting particle size can be controlled by the surface energy of the monolayer. The Fe(III)Cz-NPs were shown to be competent catalysts for the oxidation of cyclohexene with either PFIB or H(2)O(2) as external oxidant. The reactivity and product selectivity seen for Fe(III)Cz-NPs differs dramatically from that seen for the molecular species in organic solvents, suggesting that both the nanoparticle structure and the aqueous conditions may contribute to significant changes in the mechanism of action of the Fe(III)Cz catalyst.
We have shown that various porphyrin-containing nanostructures can be easily synthesized by a surfactant-assisted self-assembly (SAS) method, where an oil/aqueous medium is employed. When a chloroform solution of zinc 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (ZnTPyP) was added dropwise into cetyltrimethylammonium bromide (CTAB) aqueous solution, diverse ZnTPyP-based nanostructures, including hollow nanospheres, solid nanospheres, nanotubes, nanorods, and nanofibers, were successfully assembled. Depending on the aging time, when a low-concentration CTAB aqueous solution was employed, hollow nanospheres or nanotubes were produced. In contrast, either solid nanospheres or nanorods were obtained by using a CTAB aqueous solution in moderate concentration. Moreover, solid nanospheres or nanofibers were produced, when a high-concentration CTAB aqueous solution was used. We have further shown that the nanorods can be hierarchically organized into a regular nanoarray on silicon substrates over a large area, while the other nanostructures cannot. Interestingly, the nanorods displayed distinct supramolecular chirality although the employed ZnTPyP is achiral. On the basis of the information obtained from scanning electron microscopy, high-resolution transmission electron microscopy, fast Fourier transformation, energy-dispersive X-ray spectroscopy, X-ray diffraction, and UV-vis and circular dichroism spectra, a tentative explanation has been proposed. Our investigation suggests that the SAS method via an oil/aqueous medium is an efficient way to synthesize organic nanostructures in a controlled manner, and that such nanostructures can show different chiroptical and assembly properties.
Certain applications of supramolecular porphyrinic systems, such as molecular sieves and photonics, rely on precise nanoarchitectural control of the molecules and/or atoms; therefore they require self-assembled systems of discrete arrays and highly ordered crystals. Other applications, such as oxidation catalysts for simple substrates, may be affected by the use of self-organized materials with less supramolecular order. Colloidal porphyrin nanoparticles can be considered self-organized systems that are governed by the principles of supramolecular chemistry. The formation and potential applications of nanoparticles of these chromophores are discussed in this report with special emphasis on the parameters in the methods used to make these materials, and in terms of the supramolecular chemistry. These principles, concepts, and methodologies are applicable to a wide variety of organic dyes.
We present experimental data for the irradiance dependence of the optical nonlinearity of an organic material at different wavelengths across resonance. The material studied was a suspension of vanadyl-phthalocyanine nanocrystals in cyclohexane. The refractive and absorptive contributions to the nonlinearity were resolved by use of the z-scan technique with a tunable picosecond laser source. The observed dependence of the nonlinearity with irradiance is explained by excited-state absorption, and a three-level model is used to describe the nonlinear response. A fit to the experimental data is made, allowing the extraction of molecular parameters that are of interest for a full characterization of the nonlinearity.
meso-Tetraarylporphyrins are synthesized from pyrrole and aryl aldehydes cleanly and efficiently in one step without solvents or catalysts by reactions at temperatures 100–150 °C
above the boiling point of the starting aldehydes using air as
oxidant.
Supramolecular complex formation imparts stability and substrate selectivity to a simple manganese-porphyrin-based epoxidation catalyst. Lewis acid/Lewis base directed assembly was used to encapsulate the epoxidation catalyst within a supramolecular square structure to form an enzyme-like catalyst system. The "molecular square" takes on the functions of the protein superstructure in an enzyme: it spatially protects the catalytic core from decomposition and induces reaction selectivity.
In the ten years that have elapsed since the first edition of this book went to press, the cytochrome P450 field has completed the transition to a discipline in which structure and mechanism, even regulation and biological function, are dealt with in molecular terms. The twin forces that have propelled this remarkable progress have been the widespread adoption of molecular biological approaches and the successful application of modem structural techniques. Only a few P450 primary sequences were available in 1985, whereas hundreds of P450 sequences are now available. Site-specific mutagenesis was then mostly a proverbial gleam in the eye of the P450 community, but it is now a standard technique in the research repertoire. The first crystal structure of a cytochrome P450 enzyme had just been solved in 1985 and appeared on the cover of the first edition. Today, the high-reso lution crystal structures of four soluble bacterial P450 enzymes are available and the race is on to develop approaches that will permit us to determine the structures of the membrane-bound forms of the enzyme. The past ten years has seen phenomenal progress let us hope that the next ten will prove equally exciting. The book is informally divided into four sections. In order to hold the book close to the advancing front of research, some of the chapter topics from the first edition have been dropped to make room for new or expanded topics.
Designing nanoscale devices requires a clear understanding of the hierarchical structural organization of the functional material - from the design of the molecule, to how the molecules self-assemble into supramolecular structures, to how mese structures organize on various surfaces. Investigations comparing the structures in solution to the structures found on surfaces such as in thin films, nanoparticles, and nanoarrays, reveal the complex interplay between the energetics of selforganization and the energetics of interactions of supramolecular systems with surfaces. A perspective on the design of porphyrins that self-assemble into discrete supramolecular structures that subsequently self-organize into nanoparticles and films, and some of the factors dictating solution and surface morphology is presented.
In this third edition of Cytochrome P450: Structure, Mechanism, and Biochemistry, Dr. Paul Ortiz de Montellano has brought together a group of new authors as well as authors from previous editions to produce a timely volume that will be of considerable interest to a broad array of P450 researchers. The explosion of discovery of CYP (cytochrome P450) genes through genome analysis-more than 3500 to date-provides the more than 10,000 scientists around the world who study these monooxygenases a rich source of interesting and important research problems. Many have remained central elements over the 18 years that span the three editions of this book, including mechanisms of catalysis, oxygen activation and inhibition, gene regulation, and P450 structure. Each new edition updates our knowledge of such central issues in the study of P450s, emphasizing the timeliness of this newest volume. In this newest edition, we find that the newest discussion of P450 structure includes information of bacterial (soluble) P450s interwoven with that of eukaryotic (membrane bound) of this superfamily, highlighting the newest developments in this area. The complete battery of human P450s is now known and summarized in the new edition. In addition, general overviews of plant P450s and those from microbes contained within this newest edition provide a broader view of P450 diversity than seen in earlier editions. Each of these three editions should be on bookshelves of laboratories studying P450s. The third edition of Cytochrome P450: Structure, Mechanism, and Biochemistry provides an opportunity to judge progress in many key areas of P450 research while at the same time learn of new directions in the field. It is an excellent and most useful volume. Dr. Michael R. Waterman, Ph.D., Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN. The third edition of Cytochrome P450: Structure, Mechanism, and Biochemistry provides an exceptionally fine summary of our present knowledge of the remarkable hemoprotein often called "nature's most versatile biological catalyst." Edited by Paul Ortiz de Montellano, with chapters by many of the world's experts in this rapidly developing field, this edition includes major advances in the past decade such as the crystal structure of membrane-bound forms of the enzyme and evidence for multiple species of activated oxygen, based in part on the use of radical clocks and computational approaches. The sequences of several thousand P450s are now known, and recent progress in understanding the properties and functions of those in the microbial and plant worlds, as well as the better known mammalian isozymes, is now included. The versatility of cytochrome P450 includes the ability to metabolize innumerable substrates of both physiological and xenobiotic importance, and to be markedly altered in activity by a wide variety of inducers and inhibitors. Accordingly, this new edition will be invaluable to scientists in fields as diverse as biochemistry, chemistry, biophysics, molecular biology, pharmacology, and toxicology. M. J. Coon, Victor C. Vaughan Distinguished University Professor of Biological Chemistry, Emeritus, The University of Michigan Medical School, Ann Arbor, MI.
For Abstract see ChemInform Abstract in Full Text.
The shifts of the proton resonance lines of inert reference molecules in solution caused by paramagnetic substances are accurately given by the theoretical espression ΔH/H = (2π/3)ΔK where ΔK is the change in volume susceptibility. For aqueous solutions of paramagnetic substances, about 2% of t-butyl alcohol is incorporated, and an aqueous solution of t-butyl alcohol of the same concentration is used as an external reference. Values obtained for the susceptibility of a variety of paramagnetic molecules are in satisfactory agreement with those in the literature. Less than 0.03 ml. of a dilute solution can be studied.
A supported Mn–porphyrin catalyst has been prepared by immobilisation of the tetracationic Mn [meso-tetra (4-N-methylpyridiniumyl)porphyrin]Cl4+ on montmorillonite, and is found to be efficient for alkene epoxidation and alkane hydroxylation by PhlO, with a higher ability to oxidize alkanes, and in particular short linear alkanes, than corresponding homogeneous or silica-supported Mn–porphyrin catalysts.
A supported Mn–porphyrin catalyst was prepared by strong adsorption of the tetracationic Mn[meso-tetra(4-N-methylpyridiniumyl) porphyrin](Cl)4+4Cl– on silica, and was found very efficient for cyclo-octene epoxidation (95% yield, 13 turnovers per min) and for alkane hydroxylation, with alcohol yields and alcohol: ketone ratios remarkably higher than those obtained with corresponding soluble Mn–porphyrins.
Iron porphyrins containing perhalogenated pyrroles are found to be much better catalysts for the hydroxylation of poorly reactive alkanes like pentane or heptane by PhIO (yields as high as 80%) than the corresponding iron porphyrins without halogens on the pyrrole rings; the chemoselectivity and regioselectivity of the oxidations are found to vary very much with the presence of pyrrole halogens suggesting a dramatic change in the structure of the oxygenating iron-oxo species.
A water-chloroform interface was developed for the synthesis and assembly of the cadmium-mediated multiporphyrin arrays. With the use of a vertical dipping method, multilayers of the multiporphyrin can be deposited onto hydrophobic substrate surfaces. An in situ absorbance measurement at the water-porphyrin chloroform interface revealed a blue shift for the porphyrin Soret band after the addition of CdCl2 into the water phase. The transferred multilayers showed a broad Soret band from 430 to 442 nm, which is ascribed to monomer-like porphyrin arrangement in the planar layer and aggregates in the interlayer. The orientation angle of porphyrin macrocycles is about 30°. The porphyrin emission properties in the present multilayers are compared to those in the monomer and aggregate prepared from the air-water/CdCl2 subphase surfaces.
Chloromethylated poly(styrene) and chloropropylated silica gel have been reacted with α,ω-diamines to give diamine modified catalyst supports which have then been covalently attached to iron(III) tetrakis(pentafluorophenyl)porphyrin (FeTF5PP). In this way the diamino groups provide a simple linker/spacer unit between the support and the catalyst. The diamino-silica has been further modified using trimethylsilyl chloride and by acetylation or acid washing. The polarities of the modified inorganic and organic supports have been measured using Reichardt’s dye. Spectroscopic studies reveal that with all the supported catalysts, except that on acid washed diamino-silica where the amines are protonated, the diamino groups reduce the iron(III) porphyrin to iron(II). The supported iron porphyrins have been used to catalyse the oxidation of ethylbenzene by dioxygen. These reactions give the same three products, 1-phenylethyl hydroperoxide, 1-phenylethanol and acetophenone, as the analogous homogeneous oxidation using FeTF5PP, suggesting that they proceed by the same mechanism, however, in general they are slower. The overall product yields are limited by the stability/activity of the iron porphyrin and these in turn are very dependent on the length of the linker, the catalyst loading and the microenvironment provided by the support. The role of the diamino groups in the oxidations is discussed.
A simple kinetic model shows that a radical-chain mechanism can account for the high activity and selectivity found for oxidation of isobutane tot-butanol catalyzed by highly halogenated metalloporphyrins.
The kinetics of aerobic oxidation of cyclohexene catalyzed by Fe(III)(5,10,15,20-tetrakis(pentafluorophenyl)porphyrin)Cl in supercritical CO2 was studied at 50°C and 165atm of the total pressure with ca. 20atm O2 partial pressure. The reaction proceeded to yield allylic oxidation products, i.e. 2-cyclohexen-1-ol and 2-cyclohexen-1-one, and epoxidation products, i.e. cyclohexene oxide and 7-oxabicyclo[4,1,0]heptan-2-one. The reaction was retarded in the presence of radical inhibitor, 2,6-di-tert-butyl-4-methylphenol. The overall reaction rate under the steady state was dependent with ca. second order on the cyclohexene concentration, and zero order on the O2 concentration except for the very small O2 pressure range. These kinetic behaviors could be analyzed on the basis of the free radical allylic oxidation mechanism.
The controlled nucleophilic halide displacement reaction of [NEt4][Fe(bpc)Cl2] [H2bpc=4,5-dichloro-1,2-bis(pyridine-2-carboxamido) benzene] with AgClO4 in MeCN afforded a crystalline iron(III) complex Fe(bpc)Cl·H2O 1. The mixed chloro-dimethylformamide (DMF) axially ligated complex [Fe(bpc)Cl(DMF)] (obtained during recrystallization of 1 from DMF; however, it loses DMF quite readily to revert back to 1) has been structurally characterized. It belongs to only a handful of mononuclear high-spin iron(III) complexes having deprotonated picolinamide ligand. The iron(III) centre is co-ordinated in the equatorial plane by two pyridine nitrogens and two deprotonated amide nitrogens of the ligand, and two axial sites are co-ordinated by a chloride ion and a DMF molecule. The metal atom has a distorted octahedral geometry. Reaction of 1 with [nBu4N][OH] in MeOH afforded a μ-oxo-bridged diiron(III) complex, [Fe(bpc)]2O·DMF·2H2O, 2. The spin state and the co-ordination environment of the iron(III) centres in 1 and 2 have been determined by temperature-dependent (25–300 K) magnetic susceptibility measurements in the solid state (Faraday method) and Mössbauer spectral studies at 300 K. Complex 1 behaves as a perfect S=5/2 system, in the solid-state as well as in DMF solution. The two iron(III) centres in 2 are antiferromagnetically coupled (J=−117.8 cm−1) and the bridged dimeric structure is retained in DMF solution. Bridge-cleavage reactions of 2 have been demonstrated by its ready reaction with mineral acids such as HCl and MeCO2H to generate authentic S=5/2 complexes, [Fe(bpc)Cl2]− and [Fe(bpc)(O2CMe)2]−, respectively.
A complete set of 2H and 13C kinetic isotope effects was determined for the ene reaction of allylbenzene with maleic anhydride. Both bond formation to C1 and hydrogen transfer are implicated by the isotope effects for the rate-limiting step, and a concerted pericyclic transition state is concluded. The observed isotope effects correspond well with those predicted from Becke3LYP transition structures. These structures provide a good model for the steric interactions previously concluded to control selectivity in similar reactions.
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This paper describes the preparation of colloidal dispersions of water-insoluble organic materials by a “solvent-shifting” procedure, in which a concentrated solution of an organic solute in a water-miscible organic solvent is dispersed into a large volume of aqueous (nonsolvent) bulk solution containing colloidal stabilizers. In the majority of cases studied, the solute separates as 0.1−0.5 μm amorphous particles. The particle size is strongly correlated with the local supersaturation, i.e., the ratio of the solute feed concentration to the instantaneous value of the equilibrium solubility in the bulk, and also shows a weak dependence on the solute feed concentration. The results obtained on systematic variation of the precipitation conditions, including the amount of organic solvent in the aqueous phase, the solute feed concentration, and the mixing conditions, are discussed in terms of a mechanism of particle formation comprising dispersion of the feed solution as small droplets, followed by solvent/water counterdiffusion at the interface. Rapidly decreasing solvent quality, resulting from this interdiffusion, leads to local liquid−liquid phase separation by spinodal decomposition. This mechanism is shown to be consistent with the preferential formation of noncrystalline (amorphous) particles and with the observed changes in particle size and formation rate.
A palladium-mediated assembling strategy was developed to construct organized, three-dimensional multiporphyrin arrays, wherein layers of multiporphyrin arrays can be embedded via a Py−Pd−Py coordination unit directly on solid substrates. Multilayers of the multiporphyrin arrays were characterized by use of X-ray photoelectron, UV−vis, and fluorescence spectroscopy. A linear increase was observed for the absorption intensity of the Soret band of porphyrins or the π−π* charge transition with the layer numbers of porphyrins or palladium ions assembled. The surface density of (Zn)TPyP molecules in one layer of multiporphyrin arrays was estimated to be in the range of 1.9−2.4 × 10-10 mol/cm2. The orientation angle of the porphyrin macrocycles was in the range of 55−60°. A schematic model for the multiporphyrin arrays was proposed based on the spectral analysis, orientation angle, and film thickness from atomic force microscopy measurement. These Pd-mediated multiporphyrin arrays showed high thermal and chemical stability. They were stable in air and commonly used organic solvents. Moreover, no significant absorption spectral change was recorded in a temperature up to 150 °C and in an aqueous solution with pH < 2.
Transient absorption measurements with subpicosecond resolution have been performed on nickel(II) dodecaphenylporphyrin (NiDPP), a highly nonplanar tetrapyrrole. Following photoexcitation, NiDPP deactivates by the pathway (π,π*) → (d,d) → ground state, the route proposed previously for planar analogues. However, the (π,π*) state has now been spectrally and kinetically resolved, and evidence is presented that the deactivation proceeds mainly in the singlet manifold. The lifetime of the 1(π,π*) state of NiDPP is about 0.7 ps in all solvents investigated and increases only slightly as the temperature is reduced. The (d,d) state exhibits complex spectral evolution over the following 20 ps or more, which is interpreted in terms of vibrational relaxation and cooling, together with changes in the conformation of the porphyrin macrocycle. The ligand-field excited state decays with a lifetime of about 120 ps in toluene, but this decay time, like the vibrational and conformational dynamics in the (d,d) state, slows considerably in mineral oil and at low temperature. The solvent dependence of the ground-state absorption spectrum combined with the dependence of the excited-state kinetics on detection wavelength, viscosity, and temperature suggests that NiDPP has a number of accessible conformers and that the energies of these conformers and the barriers between them differ with the electronic state. Such conformers probably differ in the type and degree of nonplanar distortion (e.g., saddle or ruffled) and in the orientations and solvent interactions of the phenyl rings. The results presented here for NiDPP, together with previous time-resolved data on metal-free nonplanar porphyrins, suggest that key properties of nonplanar tetrapyrroles include ready access to multiple conformers and a propensity for photoinduced conformational changes. Collectively, the results of spectroscopic studies on nonplanar porphyrins suggest that static and dynamic functional properties of tetrapyrrole cofactors in vivo may be strongly modulated by the steric constraints imposed by a protein matrix.
A chiral, vaulted binaphthyl porphyrin (1) has been prepared from 5α,10β,15α,20β-tetrakis(o-aminophenyl)porphyrin and (R)-(+)-2,2′-dimethoxy-1,1′-bi-6-naphthoyl chloride in 79% yield. Asymmetric oxygenations of alkanes, alkenes, and alkyl sulfides were catalyzed with the chloroiron(III) and chloromanganese(III) complexes of 1 with good yields and high stereoselectivities. The first catalytic asymmetric hydroxylations are reported for 1-FeIIICl with enantiomeric excesses in the range of 40-72%. The corresponding manganese catalyst, 1-MnIIICl, gave much lower enantiomeric excesses. For catalytic asymmetric epoxidations, enantiomeric excesses were in the range of 20-72%. Prochiral alkyl sulfides gave sulfoxides with 14-48% ee with 1-FeIIICl.
The mechanisms of heterolytic versus homolytic O−O bond cleavage of H2O2, tert-butyl hydroperoxide (t-BuOOH), 2-methyl-1-phenyl-2-propyl hydroperoxide (MPPH), and m-chloroperoxybenzoic acid (m-CPBA) by iron(III) porphyrin complexes have been studied by carrying out catalytic epoxidations of cyclohexene in protic solvent. In these reactions, various iron(III) porphyrin complexes containing electron-withdrawing and -donating substituents on phenyl groups at the meso position of the porphyrin ring were employed to study the electronic effect of porphyrin ligands on the heterolytic versus homolytic O−O bond cleavage of the hydroperoxides. In addition, various imidazoles were introduced as axial ligands to investigate the electronic effect of axial ligands on the pathways of hydroperoxide O−O bond cleavage. Unlike the previous suggestions by Traylor, Bruice, and co-workers, the hydroperoxide O−O bonds were found to be cleaved both heterolytically and homolytically and partitioning between heterolysis and homolysis was significantly affected by the electronic nature of the iron porphyrin complexes (i.e., electronic properties of porphyrin and axial ligands). Electron-deficient iron porphyrin complexes show a tendency to cleave the hydroperoxide O−O bonds heterolytically, whereas electron-rich iron porphyrin complexes cleave the hydroperoxide O−O bonds homolytically. The heterolytic versus homolytic O−O bond cleavage of the hydroperoxides was also found to be significantly affected by the substituent of the hydroperoxides, ROOH (R = C(O)R‘, H, C(CH3)3, and C(CH3)2CH2Ph for m-CPBA, H2O2, t-BuOOH, and MPPH, respectively), in which the tendency of O−O bond heterolysis was in the order of m-CPBA > H2O2 > t-BuOOH > MPPH. This result indicates that the O−O bond of hydroperoxides containing electron-donating tert-alkyl groups such as t-BuOOH and MPPH tends to be cleaved homolytically, whereas electron-withdrawing substituents such as an acyl group in m-CPBA facilitates O−O bond heterolysis. Since we have observed that the homolytic O−O bond cleavage of hydroperoxides prevails in the reactions performed with electron-rich iron porphyrin complexes and with hydroperoxides containing electron-donating substituents such as the tert-alkyl group, we suggest that the homolytic O−O bond cleavage is facilitated when more electron density resides on the O−O bond of (Porp)Fe(III)-OOR intermediates. We also present convincing evidence that the previous assertion that the reactions of iron(III) porphyrin complexes with hydrogen peroxide and tert-alkyl hydroperoxides invariably proceed by heterolytic O−O bond cleavage in protic solvent and that the failure to obtain high epoxide yields in iron porphyrin complex-catalyzed epoxidation of olefins by hydroperoxides is due to the mechanism of heterolytic O−O bond cleavage followed by a fast hydroperoxide oxidation is highly unlike.
Syntheses, structural studies, electrochemistry, and spectroscopy of a number of [5,10,15,20-tetrakis(heptafluoropropyl)porphinato]iron derivatives are presented. The X-ray crystal structure of 5,10,15,20-tetrakis(heptafluoropropyl)porphinato]iron(II)·(pyridine)2 exhibits a substantial S4 distortion of the porphyrin macrocycle, with the meso-carbon atoms displaced more than 0.6 Å above and below the porphyrin mean plane defined by the four central nitrogen atoms; the most notable aspect of this ferrous porphyrin structure is the fact that it exhibits metrical features commonly manifested in crystallographically characterized ferric porphyrin complexes. X-ray data are as follows: P21/n with a = 12.772(1) Å, b = 18.895(2) Å, c = 19.756(2) Å, β = 99.960(6)°, V = 4695.7(8) Å3, Z = 4, and dcalc = 1.689 g/cm3. 19F NMR spectroscopy confirms the sensitivity of the 19F nucleus as a probe of macrocycle aromaticity and electronic structure, while 1H NMR spectroscopic studies show large isotropic shifts for the β-protons of the (porphinato)iron(III) chloride derivative (δ = 101.5 and 86.4 ppm). Electrochemical data obtained from cyclic voltammetric and spectroelectrochemical experiments reveal that the E1/2 value for the FeII/III redox couple for 5,10,15,20-tetrakis(heptafluoropropyl)porphinato]iron·(pyridine)2 is shifted by 550 mV relative to that observed for the corresponding (porphinato)iron(III) chloride complex. The cathodic electrochemistry of [5,10,15,20-tetrakis(heptafuoropropyl)porphinato]iron·(pyridine)2 is also unusual in that the first one-electron reduction of this complex produces a largely macrocycle-localized radical anion. EPR spectroscopic data shows that 5,10,15,20-tetrakis(heptafluoropropyl)porphinato]iron(III)·(pyridine)2 manifests a pure axial spectrum (Δ/λ = −26.4; Σg2 = 12.53) congruent with a (dxz,dyz)4(dxy)1 electronic ground state. The extraordinary structural, potentiometric, and spectroscopic properties of these (porphinato)iron species arise from substantially reduced metal-centered electron density effected by the macrocycle's non-π-conjugating, σ-electron-withdrawing meso-perfluoroalkyl substituents.
We have studied iron porphyrin complex-catalyzed oxygenations of hydrocarbons by several oxidants (i.e., hydrogen peroxide, tert-butyl hydroperoxide, and m-chloroperoxybenzoic acid (MCPBA)) in the presence of H218O. In the olefin epoxidation and alkane hydroxylation reactions catalyzed by (meso-tetrakis(pentafluorophenyl)porphinato)iron(III) chloride [Fe(F20TPP)Cl], the percentages of 18O incorporated into the oxygenated products were found to be the same in all of the reactions of hydrogen peroxide, tert-butyl hydroperoxide, and MCPBA, leading us to conclude that a common high-valent iron oxo complex was the reactive intermediate responsible for oxygen atom transfer. When the epoxidation of cyclooctene by MCPBA and H2O2 was performed at low temperature in the presence of H218O, it was found that there was no 18O-incorporation from labeled water into cyclooctene oxide. We interpreted the lack of 18O-incorporation in these reactions with that an electronegatively-substituted iron porphyrin complex forms a relatively stable (Porp)FeIII−OOR species and this intermediate transfers its oxygen to olefin prior to the O−O bond cleavage at low temperature. As the reaction temperature raised from −78 °C to room temperature, the amount of 18O incorporated into the oxide product gradually increased in the reactions of cyclooctene epoxidation. This was attributed to the fast conversion of FeIII−OOR to the high-valent iron oxo complex via the O−O bond cleavage at higher temperature. We found, by studying the effects of the olefin and H218O concentrations on the amount of 18O incorporated into the oxide product, that the rate of the oxygen exchange between high-valent iron oxo complex and labeled water was slower than that of the oxygen atom transfer from the intermediate to organic compounds in catalytic oxygenation reactions. Blocking an axial position of iron porphyrin complex with imidazole prevented the 18O-incorporation from labeled water into the oxygenated products, explaining the phenomenon of no oxygen exchange in cytochrome P-450 systems.
1. Monodispersed colloids exhibiting higher order Tyndall spectra have been prepared by precipitation of sulfur from ethanol and acetone solutions by the careful addition of water. 2. The relationship between the concentration of sulfur and the volume fraction of water at the critical point of sulfur-ethanol-water solutions has been investigated. 3. Sols prepared by this dilution method have been investigated as to dispersion of wave length in their angular scattering of visible light and their transmission as a function of wave length. 4. The size, number and charge of the particles of such sols are in the same range as those prepared by the acid decomposition of sodium thiosulfate. 5. The rates of growth of sols prepared by such a dilution method have been investigated. The growth rates obtained have been reproduced from previous theoretical considerations which allow the estimation of the value of the diffusion coefficient of S 8 in alcohol-water and acetone-water mixtures. The value of this diffusion coefficient lies in the range 7-8 × 10 -6 cm. 2/sec. for both media. The application of this method for estimating diffusion coefficients is valid for any colloidal system that is characterized by a small particle size distribution at all stages of its growth. 6. A qualitative explanation is offered for the necessary conditions under which monodispersed colloids may be prepared for both the dilution and acid decomposition of sodium thiosulfate methods.
Die Porphin-Komplexe (I) und (IIa) katalysieren die Epoxidation und Hydroxylierung von Kohlenwasserstoffen mit Iodosylbenzol (IV): Aus Cyclohexen (III) bzw. -hexadien (VII) werden die Epoxide (V) (daneben das Cyclohexenol (VI)) bzw. (VIII) gebildet; cis- (IXa) und trans-Stilben (IXb) geben mit (IIa) als Katalysator das cis- (X) bzw. trans-Epoxid (XI), während mit (I) als Katalysator (IXb) inert bleibt (Diskussion der Gründe hierfür).
The kinetics and equilibria for binding carbon monoxide or dioxygen to the previously described adamantane-heme-[6.6]cyclophane were changed very little by substituting the internally hydrogen-bonded base, 4-(2-N-piperidylethyl)imidazole for 1,5-dicyclohexylimidazole. By contrast, the rate of reaction of protohemin dimethyl ester chloride with tert-butyl hydroperoxide was accelerated by substitution of the internally hydrogen-bonded base for N-methylimidazole. We conclude that hydrogen bonding of the proximal imidazole increases peroxidase activity of iron(III) porphyrins but does not greatly affect oxygen affinity of iron(II) porphyrins.
The effect of solvent polarity and acidity and the solvent isotope effects on the reaction of iron(III) porphyrins with hydrogen peroxide, tert-butyl hydroperoxide, and peracids have been investigated. Both the solvent isotope effects on the reactions of hydroperoxides with hemins are almost identical with these effects on the reactions of hydroperoxides with dialkyl sulfides and the effects on the reaction of peracids with iron(III) porphyrins. Since both of the latter reactions are known to involve heterolytic cleavage of the O-O bond, this similarity provides strong evidence for heterolytic cleavage of hydroperoxide by reaction with hemins. The strong alcohol catalysis of the studied reactions provides a mechanistic rationale for the O-O bond cleavage in cytochrome P-450 in terms of general-acid catalysis by water in the enzyme site.
The first direct observation of the push effect on heterolytic and homolytic O-O bond cleavage steps of acylperoxoiron(III) porphyrin complexes is reported for a series of acylperoxoiron(III) porphyrins (5) having substituents at the meso-positions of the porphyrin ring. Transformation of 5 to the corresponding oxoferryl (O=Fe(IV)) porphyrin cation radicals (6) in methylene chloride at -80-degrees-C by heterolytic O-O bond cleavage was found to be first order in [5]. Introduction of electron-donating substituents at the meso-positions of the porphyrin ring facilitates the O-O bond cleavage in 5. Addition of 1 equiv of imidazole derivatives to a methylene chloride solution of 5 immediately gave an acylperoxoiron(III) porphyrin-imidazole adduct (9). The conversion of 9 to 6 was also found to be first order in [91, and the coordination of electron-rich imidazole derivatives strongly encouraged the O-O bond cleavage of 9. On the other hand, the push effect on the homolytic O-O bond cleavage reaction has been examined in toluene at -6-degrees-C to about -40-degrees-C. The homolytic O-O bond cleavage of 9 afforded the imidazole adduct of oxoferryl porphyrin complex 7 when phenylperacetic acid was employed. Homolysis of the O-O bond is enhanced by the imidazole ligation; however, the push effect on homolysis is much less than that on heterolysis. These results explain the biological utilization of strong electron-donor ligands in heme enzymes such as peroxidase, cytochrome P-450, and catalase.
Molecular structures of both Fe{sup III}(TFPPBrâ) Cl and Fe{sup II} (TFPPBrâ)(py)â porphyrins reveal saddle distortions: Fe{sup III-} (TFPPBrâ)Cl in triclinic space group P1, a = 13.649(4) â«, c = 14.537 â«, α = 89.26(2)°, β = 67.13(1)°, γ = 71.82(2)°, V = 2494.3(13) â«Â³, Z = 2 ; Fe{sup III}(TFPPBrâ)(py)â in triclinic space group P1, a = 12.459- (7) â«, b = 13.125(8) â«, c = 20.989(11) â«, α = 84.72(5)°, β = 72.87(4)°, γ = 69.04(5)°, V = 3063(3) â«Â³, Z = 2. Similar to other chloro-iron(III) porphyrins. μ{sub eff} at room temperature (5.96 μ{sub B}) is that of a â¶Aâ state; μ{sub eff} at 2 K (4.2μ{sub B}) indicates a large zero-field splitting. The Soret bands of both Fe{sup III}(TFPPBrâ)Cl and Fe{sup II}(TFPPBrâ)- (py)â are red-shifted by approximately 23 nm relative to those of corresponding planar Fe{sup III} porphyrins. The metal and porphyrin reduction potentials of Fe{sup III} (TFPPBrâ)Cl and Fe{sup II}(TFPPBrâ)(py)â are anodically shifted more than 400 mV from those of Fe{sup III}(TPP)Cl. Although [Fe{sup II}(TFPPBrâ)Cl]- reacts very slowly with dioxygen, it is oxidized rapidly by tert-butyl hydroperoxide (TBHP); these Fe{sup III} reactivity properties taken together with the finding that the corresponding Fe{sup III} complex is reduced rapidly by TBHP provide strong support for the proposal that Fe{sup III}(TFPPBrâ)Cl/Oâ-catalyzed alkane oxygenations occur by a radical chain mechanism in which alkyl hydroperoxide intermediates are decomposed efficiently by both Fe{sup III} and Fe{sup III} species.
Critical examination of the analysis of paramagnetic susceptibility by NMR spectroscopy. Keywords (Audience): Upper-Division Undergraduate
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The lifetime of the (d z 2 ,d x 2 -y 2) metal excited state of nickel(II) 5,10,15,20-tetra-tert-butylporphyrin (NiT(t-Bu)P) exhibits an extraordinary dependence on solvent dielectric properties and temperature. At room temperature, the excited-state deactivation time varies from 2 ps in highly polar solvents to about 50 ns in nonpolar media. The lifetimes increase to several microseconds in both polar and nonpolar solvents near 80 K. In contrast, the (d,d) lifetimes of nominally planar nickel porphyrins such as nickel tetraphenylporphyrin (NiTPP) vary only weakly with solvent dielectric properties and temperature, and typically fall in the range of 100 to 300 ps. All available evidence indicates that NiT(t-Bu)P in solution is highly ruffled (nonplanar) in the ground electronic state. It is proposed that the photoinduced conformational changes that occur in NiT(t-Bu)P in order to accommodate the excited-state electronic distribution are limited by the severe steric constraints imposed by the bulky meso tert-butyl substituents, and result in molecular and electronic asymmetry and thus a polar excited state. Solvent dielectric properties and temperature modulate these conformational excursions and thus the electronic deactivation rates by affecting the excited-state energies, porphyrin/solvent reorganiza-tions, and the populations of low-frequency out-of-plane vibrations of the macrocycle. The novel findings for this nonplanar nickel porphyrin demonstrate the intimate connectivity that exists between the static and dynamic molecular structures of porphyrins and their ground-and excited-state electronic properties. Furthermore, the results obtained provide insights into the interactions between tetrapyrrole chromophores and their host proteins, and suggest the potential use of nonplanar porphyrins as building blocks for molecular photonics applications.
1 2 3 4 7 rph3 Pd-Er I PPh 8 is therefore entirely possible that, unlike Trost's reaction of a-allylpalladium derivatives with "soft" carbanions which has been shown to involve the backside attack of a-allylpalladium cations by the carbanionic species,8 our reaction might involve attack of u-allylpalladium derivatives by organometals via transmetalation which is followed by reductive elimination, as we have suggested for various other Pd-catalyzed cross-coupling reactions.2 Acknowledgment. We thank the National Institutes of Health and the Japan Tobacco & Salt Public Corp. for support of this research.
Metallvermittelte Oxofunktionalisierungen organischer Substrate sind von fundamentaler Bedeutung – in der Natur genauso wie in Hochschul- und Industrielaboratorien. Ungeachtet dessen sind die Mechanismen dieser Reaktionen rätselhaft geblieben, und nur wenige Prozesse werden im Detail verstanden. Dank intensiver Forschung konnte der Wissensstand in den letzten Jahren aber erheblich verbessert werden: So wurde gezeigt, dass viele Oxygenierungen über Radikalintermediate verlaufen – mitunter auch dann, wenn eine vergleichsweise hohe Selektivität Gegenteiliges vermuten lässt. Das zeigen Beispiele aus den unterschiedlichsten Bereichen: von molekularen Metalloxokomplexen, gasförmigen und matrixisolierten Spezies über das Reaktionsverhalten von Metalloenzymen bis hin zu Prozessen an Festkörperoberflächen. Der vorliegende Aufsatz beleuchtet die Vielfalt dieser Systeme und vermittelt einen Überblick über allgemein gültige Reaktionsmuster und Prinzipien sowie einige noch ungelöste Probleme.
Viele organische Wirk- und Effektstoffe sind in Wasser schwer löslich oder sogar unlöslich. Wässrige Anwendungsformen erfordern daher besondere Formulierungsverfahren, um die physiologische (Pharma, Kosmetik, Pflanzenschutz, Ernährung) oder technologische Wirkung (Lacke, Druckfarben, Toner) nutzen zu können oder zu optimieren. Zu den interessantesten Eigenschaften nanodisperser Verteilungen organischer Wirk- und Effektstoffe gehören die drastische Erhöhung der Löslichkeit, die Verbesserung der biologischen Resorption sowie die Modifizierung optischer, elektrooptischer und anderer physikalischer Eigenschaften, die erst mit Teilchengrößen im mittleren und unteren Nanometerbereich (50–500 nm) erzielbar sind. So sind es neben ökonomischen und ökologischen Zwängen auch technologische Herausforderungen, die als Alternative zu den etablierten mechanischen Zerkleinerungsverfahren die Entwicklung neuer Verfahren zur Herstellung organischer Nanopartikel als dringend geboten erscheinen lassen. In diesem Sinne sind in jüngster Zeit vermehrt Forschungsaktivitäten zu verzeichnen, die die kontinuierliche, automatisierte Herstellung nanodisperser Systeme durch Fällung aus molekularer Lösung zum Ziel haben. Im vorliegenden Aufsatz wird der aktuelle Kenntnisstand zu den Grundlagen der Partikelbildung aus homogener Lösung, zum Einfluss des Lösungsmittels und polymerer Additive auf die Morphologie und auf die supramolekulare Struktur der Nanopartikel dargestellt. Anhand der sowohl physiologisch als auch technologisch interessanten Stoffklasse der Carotinoide wird die praktische Umsetzung dieser neuen Formulierungstechnologie eingehend erläutert.
In der jüngsten Vergangenheit ist das Interesse an der Katalyse mit Nanopartikeln (NPs) stark gestiegen, wie zahlreiche Publikationen auf diesem Gebiet aus den letzten fünf Jahren belegen. Dieser Bereich der “semi-heterogenen” Katalyse bildet die Nahtstelle zwischen homogener und heterogener Katalyse. Aktuelle Fortschritte betreffen die Effizienz und Selektivität der Reaktionen sowie die Rückgewinnung und Regenerierbarkeit des katalytischen Materials. Gewöhnlich werden die NP-Katalysatoren aus einem Metallsalz, einem Reduktionsmittel und einem Stabilisator hergestellt und auf einem Oxid-, Aktivkohle- oder Zeolithträger fixiert. Neben den früher hauptsächlich eingesetzten Polymeren und Oxiden finden inzwischen auch neuartige Stabilisatoren, Medien und Trägermaterialien Anwendung, darunter Dendrimere, spezifische Liganden, ionische Flüssigkeiten, Detergentien, Membranen, Kohlenstoff-Nanoröhren und eine Vielzahl von Oxiden. Auch mit ligandenfreien Verfahren wurden jüngst bemerkenswerte Ergebnisse bei sehr geringer Metallbeladung erreicht. Dieser Aufsatz diskutiert die neueren Entwicklungen und die Anwendung von katalytischen Metallnanopartikeln in der organischen Synthese, z. B. in Hydrierungen und C-C-Kupplungen sowie in der heterogenen Oxidation von CO durch Gold-NPs.
Supramolecular complex formation imparts stability and substrate selectivity to a simple manganese-porphyrin-based epoxidation catalyst. Lewis acid/Lewis base directed assembly was used to encapsulate the epoxidation catalyst within a supramolecular square structure to form an enzyme-like catalyst system. The “molecular square” (see picture) takes on the functions of the protein superstructure in an enzyme: it spatially protects the catalytic core from decomposition and induces reaction selectivity.
Manganese(III) 5-(pentafluorophenyl)-10,15,20-tri(2,6-dichlorophenyl)porphyrin, Mn(PFTDCPP), and manganese(II) 2,3,7,8,12,13,17,18-octachloro-5-(pentafluorophenyl)-10,15-20-tri(2,6-dichlorophenyl)porphyrin, Mn(PFTDCCl8PP), have been synthesised and used as catalysts in hydrocarbon oxidations by iodosylbenzene and hydrogen peroxide both in solution and covalently bound to aminopropylated silica. The former shows higher efficiency in the epoxidation of alkenes by iodosylbenzene, whereas the perchlorinated manganese porphyrin is more efficient in the hydroxylation of alkanes by this oxidant. The supported manganese(III) porphyrin show the same activity as its homogeneous analogue. With hydrogen peroxide as oxygen donor, Mn(PFTDCPP) is a stable and effective catalyst in the presence of imidazole. The perchlorinated analogue is a poor catalyst with this oxidant. The eight additional chlorine atoms on the porphyrin ring stabilise Mn(II) and unfavour the formation of the active species, MnVO.