Metalloporphyrin Complexes Research Articles

Hydrogen Generation Catalyzed By Metalloporphyrins

Hydrogen has potential of being used as the future green fuel in fuel cells. The demand and consumption of hydrogen have predicted to continuously rise in the next two decades. Nevertheless, a highly efficient and low cost of water-splitting catalyst for hydrogen generation remains elusive. In this presentation, we synthesize a series of metalloporphyrin complexes in order to elucidate the effects of porphyrinic structure to the catalytic efficiencies. It is found that the metalloporphyrins with different substituents demonstrated different catalytic activities. A porphyrin with acidic substituents appears to be essential to offer high catalytic efficiencies. Additionally, a substituent located closer to the metal ion center will be better than oriented outward in respect to the central core. Our results also suggest that the type of central metal ions is another factor that control the activity of the hydrogen generation catalysts. Through the comparison on the CV of two novel N-confused porphyrin cobalt nitrosyl complexes, it appears that the activities of the catalysts depend on the reduction sites where the reducing equivalent will reside, i.e. a Co(NO) moiety based reduction has a more positive onset potential than a porphyrin-based reduction.

Base-Promoted Vinyl Carbon–Bromine Bond Cleavage by Group 9 Metalloporphyrin Complexes

Base-promoted vinyl carbon–bromine bond cleavage of styryl bromide by group 9 metalloporphyrin complexes was achieved to give the metal(III) porphyrin styryls M(ttp)(styryl) (ttp = 5,10,15,20-tetra-p-tolylporphyrinato dianion). Mechanistic studies suggest that [MII(ttp)]2 (M = Rh, Ir) cleaves the vinyl C–Br bond via an addition–elimination mechanism. The much less reactive CoII(ttp) undergoes a radical recombination with styryl radical which is generated by the hydroxide reduction of styryl bromide to give a radical anion with subsequent C–Br cleavage.

Synthesis and Characterization of a New Proline Tailed Porphyrin and Its Metalloporphyrin Complexes

In this study, the authors synthesized and characterized a new proline tailed porphyrin, 5-[4-N-(tert-butoxycarbonyl)-L-prolinecoxyl propyloxy]phenyl-10,15,20-triphenylporphyrin and its metalloporphyrin complexes. The porphyrins 1–4 have been characterized by UV/Vis, IR, NMR, MS and CD spectra techniques. And the structure of the compounds was confirmed by analyzing of those spectra. Furthermore, the CD spectrum studies showed that porphyrins 1–4 have chiral molecule, and their CD spectra were split in the Soret band and have cotton effect. Metalloporphyrin coordination ability and the optimum configuration of these metalloporphyrin complexes were calculated by chemical simulation. Besides, the coordination ability of porphyrin 1 and its Zn, Ni, Co complexes were predicted. According to the result of optimization and quantitative molecular calculation, shows the most stable structure at all of possible structure in the subject molecule and object molecule.

X-ray Structure and Properties of the Ferrous Octaethylporphyrin Nitroxyl Complex.

The preparation and characterization of the iron octaethylporphyrin nitroxyl ion, [Fe(OEP)(NO)(-)], is reported. The complex was synthesized by the one-electron reduction of Fe(OEP)(NO) using anthracenide as the reducing agent. The compound was isolated as the potassium (2.2.2)cryptand salt. The anion was characterized using X-ray analysis with visible and infrared spectroscopy. The spectral features of the iron nitroxyl complex were consistent with previous literature reports. The important structural changes upon reduction were a significant decrease in the Fe-N-O bond angle from 142° to 127° and an increase in the N-O bond length from that in the starting nitrosyl moiety. The porphyrin ring became significantly less planar upon reduction, but the displacement of the iron atom from the 24-atom plane was essentially unchanged. In spite of the attempt to encapsulate the potassium ion with the (2.2.2)cryptand, significant interaction between K(+) and the oxygen of the nitroxyl were observed, indicating a contact ion pair in the crystal structure. Comparison between the experimental structure and the DFT-calculated parameters were reported. The results are consistent with the Fe-N-O moiety being the site of the reduction, with little evidence for the reduction of the iron itself or the porphyrin ring. The proton NMR spectrum was also obtained, and the chemical shifts were significantly different from other S = 0 metalloporphyrin complexes. These shifts, though, were consistent with the DFT calculations.

Discrete multiporphyrin pseudorotaxane assemblies from di- and tetravalent porphyrin building blocks.

Two pairs of divalent and tetravalent porphyrin building blocks carrying the complementary supramolecular crown ether/secondary ammonium ion binding motif have been synthesized and their derived pseudorotaxanes have been studied by a combination of NMR spectroscopy in solution and ESI mass spectrometry in the gas phase. By simple mixing of the components the formation of discrete dimeric and trimeric (metallo)porphyrin complexes predominates, in accordance to binding stoichiometry, while the amount of alternative structures can be neglected. Our results illustrate the power of multivalency to program the multicomponent self-assembly of specific entities into discrete functional nanostructures.

Coordination and crystallization molecules: their interactions affecting the dimensionality of metalloporphyrinic SCFs.

Synthetic metalloporphyrin complexes are often used as analogues of natural systems, and they can be used for the preparation of new Solid Coordination Frameworks (SCFs). In this work, a series of six metalloporphyrinic compounds constructed from different meso substituted metalloporphyrins (phenyl, carboxyphenyl and sulfonatophenyl) have been structurally characterized by means of single crystal X-ray diffraction, IR spectroscopy and elemental analysis. The compounds were classified considering the dimensionality of the crystal array, referred just to coordination bonds, into 0D, 1D and 2D compounds. This way, the structural features and relationships of those crystal structures were analyzed, in order to extract conclusions not only about the dimensionality of the networks but also about possible applications of the as-obtained compounds, focusing the interest on the interactions of coordination and crystallization molecules. These interactions provide the coordination bonds and the cohesion forces which produce SCFs with different dimensionalities.

Photocatalytic Oxidation of 2-Mercaptoethanol to Disulfide using Sb(V)-, P(V)-, and Ge(IV)-porphyrin Complexes

Visible-light irradiation of MeCN solution containing di(hydroxo)metallo(tetraphenyl)porphyrin complex <TEX>$(tppM(OH)_2$</TEX>: 1a; <TEX>$M=Sb(V)^+Br^-$</TEX>, 1b; <TEX>$M=P(V)^+Cl^-$</TEX>, 1c; M=Ge(IV)) and 2-mercaptoethanol (2-ME) as a substrate under aerated condition gave bis(2-hydroxyethyl)disulfide (2-HEDS) as an oxidative product of 2-ME. It is indicated that the oxidation of 2-ME should proceed with a photocatalytic process by 1, because the turn over number (TON) for the formation of 2-HEDS was over unit. The TON was determined to be 642 as a maximum value when 1a was used as a sensitizer. The formation of 2-HDES was extremely slow under argon atmosphere. The fluorescence of 1 was not quenched by 2-ME at all, and the free energy change (<TEX>${\Delta}G$</TEX>) with electron transfer (ET) from 2-ME to excited triplet state of <TEX>$1(^31^*)$</TEX> was estimated as a negative value. The quenching rate constant (<TEX>$k_r$</TEX>) of <TEX>$^31^*$</TEX> by 2-ME, obtained by the kinetics for the formation of 2-HEDS, strongly depends on <TEX>${\Delta}G$</TEX>. These findings indicate that 1-sensitized oxidation was initiated by photoinduced ET from 2-ME to <TEX>$^31^*$</TEX> to generate both radical cation of 2-ME (<TEX>$2-ME^{+\bulle}$</TEX>) and porphyrin radical anion (<TEX>$1^{-\bulle}$</TEX>), resulting that the formation of 2-HEDS can be proceeded by the dimerization of <TEX>$2-ME^{+\bulle}$</TEX>, and through a catalytic cycle due to returning to 1 by the ET from <TEX>$1^{-\bulle}$</TEX> to molecular oxygen.

Effect of imidazole on biomimetic cyclohexane oxidation by first-, second-, and third-generation manganese porphyrins using PhIO and PhI(OAc)2 as oxidants

In this work, spectrophotometric titrations of first- (MnIIITPPCl), second- (MnIIIAPTPPCl and MnIIIT4CMPPCl), and third- (MnIIIBr9APTPPCl and MnIIIBr8T4CMPPCl) generation manganese(III) porphyrins ([MnIIIP]+) were carried out in order to investigate the axial coordination equilibrium between imidazole (Im) and these metalloporphyrin complexes. Cyclohexane oxidation by PhIO or PhI(OAc)2 catalyzed by the aforementioned [MnIIIP]+, in the presence of various [MnIIIP]+/Im molar ratios, was investigated as a means to study the contribution that the penta-, [MnIIIP(Im)]+, or hexacoordinate, [MnIIIP(Im)2]+, species at equilibrium may exert into catalyst efficiency and oxidative stability. The computational program SQUAD was used to analyze the spectrophotometric data and calculate the equilibrium constants used by program HySS to generate the species distribution curves for the various [MnIIIP]+/Im systems. In general, higher catalytic efficiency in the PhIO systems was achieved with the use of imidazole ranging from 1:0.5 to 1:5 [MnIIIP]+/Im ratio, depending on the nature of [MnIIIP]+. The catalytic systems with PhI(OAc)2 as oxidant were more sensitive to Im addition, and optimum yields were achieved with lower [MnIIIP]+/Im ratio (up to 1:1). It is noteworthy that the presence of imidazole reduced the usual instability of the third-generation catalyst MnIIIBr8T4CMPPCl toward oxidative destruction by PhI(OAc)2, but did not exert such a protective effect in the PhIO oxidations.

Evaluation of Laser Desorption Ionization Coupled to Fourier Transform Ion Cyclotron Resonance Mass Spectrometry To Study Metalloporphyrin Complexes

In this study, the applicability of positive-ion (+) laser desorption ionization (LDI) as an ionization method for metalloporphyrin complexes was evaluated. The evaluation was performed by analyzing standard compounds and a series of crude oils with various V4+ and Ni2+ contents by (+) LDI and (+) atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The analysis of standard compounds showed that molecular ions were main ionic species in (+) LDI. Fragmented ions because of the loss of CH3 were also observed. The analysis of crude oils showed that the sensitivity of (+) LDI toward metalloporphyrin complexes is greater than that of (+) APPI. Furthermore, five types of ion VO2+ and Ni2+ porphyrin complexes (etio, DPEP, rhodo-etio, rhodo-DPEP, and di-DPEP) were observed with (+) LDI, but only three types were observed with (+) APPI. Nickel porphyrins were observed in unfractionated oils by (+) LDI but not by (+) APPI. The summed relative abundance...

A green and sustainable method for the oxidation of 1,3-dihydrobenzo[c]thiophenes to sulfones using metalloporphyrin complexes

Two efficient methods are reported for the oxidation of 1,3-dihydrobenzo[c]thiophenes to sulfones in good to high yields using H2O2 in the presence of catalytic amounts of porphyrin-based catalysts in ethanol or acetonitrile as solvents at room temperature. The presence of electron-donating or electron-withdrawing groups, in the benzene ring of 1,3-dihydrobenzo[c]thiophene, is well tolerated.

Glycol metalloporphyrin derivatives in solution or immobilized on LDH and silica: synthesis, characterization and catalytic features in oxidation reactions

We reacted [meso-tetrakis(pentafluorophenyl)porphyrin] with ethylene glycol to obtain porphyrins substituted with one to four hydroxyalkyloxy groups at position 4 of the meso-aryl groups. We then inserted iron(III) or manganese(III) into the mono- and tetra-substituted free-base derivatives, which afforded the corresponding metalloporphyrin complexes. Next, we immobilized the iron(III) and manganese(III) porphyrins on two supports: layered double hydroxide (LDH) and silica (synthesized by the sol–gel process). We characterized the resulting solids using powder X-ray diffraction (PXRD), UV–vis electronic spectroscopy, and electron paramagnetic resonance (EPR), and we investigated the catalytic activity of the materials in both homogeneous and heterogeneous media. The metalloporphyrins provided good catalytic conversions in (Z)-cyclooctene oxidation. As for cyclohexane oxidation, the catalysts were selective for the alcohol instead of the ketone. In the case of heterogeneous catalysis, the immobilized metalloporphyrins furnished slightly lower yields as compared with homogeneous catalysis. However, these solids presented a major advantage: reusability. Indeed, these solid catalysts retained their activity for at least three cycles in the case of (Z)-cyclooctene oxidation.

Intermolecular iodine–iodine interactions in bis(pyridine-3-carboxylato)[tetrakis(4-iodophenyl)porphyrinato]tin(IV) and bis(pyrimidine-5-carboxylato)[tetrakis(4-iodophenyl)porphyrinato]tin(IV)

Crystals of bis(pyridine-3-carboxylato)[tetrakis(4-iodophenyl)porphyrinato]tin(IV) dimethylformamide sesquisolvate, [Sn(C44H24I4N4)(C6H4NO2)2]·1.5C3H7NO, (I), and bis(pyrimidine-5-carboxylato)[tetrakis(4-iodophenyl)porphyrinato]tin(IV) dimethylformamide sesquisolvate, [Sn(C44H24I4N4)(C5H3N2O2)2]·1.5C3H7NO, (II), exhibit interporphyrin iodine-iodine halogen bonds, which direct the supramolecular assembly of the porphyrin entities into halogen-bonded layers. Each molecule interacts with its four nearest neighbours within the layer via eight I···I interactions at approximately 3.8 and 4.0 Å. The two structures are isomorphous and isometric, with the metalloporphyrin complexes located on centres of crystallographic inversion.

A SO2-selective electrode based on a Zn-porphyrin for wine analysis

This work describes the assessment of a SO2-selective electrode based on the use of the neutral carrier 5,10,15,20-tetraphenyl(porphyrinate)zinc(II) in a PVC membrane plasticized with 2-nitrophenyl phenyl ether. After being conditioned in 2molL−1 diethylamine solution for 24h, the electrode exhibited selective anionic response toward the analyte in a concentration interval of more than four decades, with an slope of −59.5mVdec−1, a practical detection limit of 3.7×10−6molL−1 and a low limit of linear range of 7.2×10−6molL−1. The response mechanism is based on the displacement of the diethylamine:metalloporphyrin complex equilibrium within membrane bulk, inducing a variation in the cationic-sites to ionophore ratio. In turn, free hydroxyl ions are complexed by the displaced ionophore in a ratio 1:1 and translated as single negative charge nernstian response. Finally, the selectivity of the electrode is evaluated in view of its application to wine analysis. Results had high accuracy and precision when compared with a reference method.

Direct observation of intermediates formed during steady-state electrocatalytic O 2 reduction by iron porphyrins

Heme/porphyrin-based electrocatalysts (both synthetic and natural) have been known to catalyze electrochemical O2, H(+), and CO2 reduction for more than five decades. So far, no direct spectroscopic investigations of intermediates formed on the electrodes during these processes have been reported; and this has limited detailed understanding of the mechanism of these catalysts, which is key to their development. Rotating disk electrochemistry coupled to resonance Raman spectroscopy is reported for iron porphyrin electrocatalysts that reduce O2 in buffered aqueous solutions. Unlike conventional single-turnover intermediate trapping experiments, these experiments probe the system while it is under steady state. A combination of oxidation and spin-state marker bands and metal ligand vibrations (identified using isotopically enriched substrates) allow in situ identification of O2-derived intermediates formed on the electrode surface. This approach, combining dynamic electrochemistry with resonance Raman spectroscopy, may be routinely used to investigate a plethora of metalloporphyrin complexes and heme enzymes used as electrocatalysts for small-molecule activation.

Iridium Porphyrin Catalyzed N–H Insertion Reactions: Scope and Mechanism

Ir(TTP)CH3 catalyzed N–H insertion reactions between ethyl diazoacetate (EDA) or methyl phenyldiazoacetate (MPDA) and a variety of aryl, aliphatic, primary, and secondary amines to generate substituted glycine esters with modest to high yields. Aniline substrates generally gave yields above 80%, with up to 105 catalyst turnovers, and without slow addition of the diazo reagent. Good yields were also achieved with aliphatic amines, though higher catalyst loadings and slow addition of the amine were necessary in some cases. Primary amines reacted with EDA to generate both single- and double-insertion products, either of which could be produced selectively in high yield with the proper choice of stoichiometric ratios and reaction temperature. Notably, mixed trisubstituted amines, RN(CH2CO2Et)(CHPhCO2Me), were generated from the insertion of 1 equiv of EDA and 1 equiv of MPDA into primary amines. The N–H insertion mechanism was examined using substrate competition studies, trapping experiments, and multiple spectroscopic techniques. Substrate competition studies using pairs of amines with EDA or MPDA revealed Hammett correlations with respective slopes of ρ = 0.15 and ρ+ = −0.56 as well as kinetic isotope ratios of kH/kD = 1.0 ± 0.2 and 2.7 ± 0.2. Competitive amine binding to the iridium center was demonstrated by kinetics and equilibrium binding studies. Equilibrium binding constants ranged from 102 to 105. Monitoring the reaction by absorption spectroscopy revealed a transient metalloporphyrin complex. The lifetime of this species was dependent on the nature of the amine substrate, which suggests that the catalytic cycle proceeds through a metal–ylide intermediate.

Selective oxidation of benzyl alcohol to benzaldehyde over Co-metalloporphyrin supported on silica nanoparticles

Heterogenation of the metalloporhyrin ligand, [tetrakis(o-chlorophenyl)porphyrinato]Co(II) was effected by immobilizing the complex onto inorganic silica support to form spherical nanoparticles of RHAC-CoPor. This insoluble mesoporous hybrid showed a high specific surface area of 114m2g−1 and a pore volume of 0.177cm3g−1. The prepared catalyst possessed a narrow pore size distribution centered at around 4.17nm. The 13C MAS NMR showed that RHAC-CoPor had three chemical shifts at 12.60, 26.60 and 45.18ppm consistent with the three carbon atoms of the propyl group and a series of chemical shifts in the range of δ=108–167ppm consistent with the presence of the metalloporphyrin complex. Elemental analysis showed the successful immobilization of metalloporphyrin complex onto functionalized RHA silica support. RHAC-CoPor appeared to be an active catalyst in the oxidation of benzyl alcohol, producing 97.1% conversion and 97.7% selectivity for benzaldehyde under an ambient temperature of 70°C. RHAC-CoPor could be regenerated and reused several times by washing with water, followed by drying at 100°C.

Carbon Dioxide Fixation by Cycloaddition with Epoxides, Catalyzed by Biomimetic Metalloporphyrins

AbstractSeveral biomimetic metalloporphyrin complexes (M(TPP)XY; in which TPP=meso‐porphyrin; M=MgII, AlIII, SnII, or SnIV; X=OAc, F, Cl, Br, I, OTf, or none; and Y=Cl, Br, I, OTf, or none) were prepared, characterized, and used effectively in the “green” synthesis of cyclic carbonates from epoxides and CO2. The catalytic systems of Mg(TPP)/tetrabutylammonium iodide and Al(TPP)Cl/phenyltrimethyl ammonium tribromide can initiate the cycloaddition of epoxides and CO2 at room temperature to generating cyclic carbonates in excellent yield. Chlorophyll A is shown to induce enantioselectivity of racemic propylene oxide. All reactions displayed excellent selectivity to cyclic carbonate without polycarbonate and other by‐products. Chloropropylene carbonate is shown to be obtained under CO2 bubbling conditions catalyzed by Al(TPP)Cl/phenyltrimethylammonium tribromide. The catalytic order of activity for biomimetic metalloporphyrins is AlIII&gt;MgII&gt;SnIV&gt;SnII. These phenomena are explained with respect to the Lewis acidity of metal center in metalloporphyrins.

C–H Insertion Catalyzed by Tetratolylporphyrinato Methyliridium via a Metal–Carbene Intermediate

C–H insertion reactions between different substrates and diazo reagents were catalyzed by tetratolylporphyrinato methyliridium (Ir(TTP)CH3). The highest yields were achieved for reactions between the bulky diazo reagent methyl 2-phenyldiazoacetate (MPDA) and substrates containing electron-rich C–H bonds. An intermediate metalloporphyrin complex was identified as a metal–carbene complex, Ir(TTP)(═C[Ph]CO2CH3)(CH3) (4), using 1H NMR and UV/vis absorption spectroscopy. The presence of 4 was further supported by computationally modeling the absorption spectra with time-dependent DFT (6-31G(d,p)/SBKJC basis set, PBE0 functional). Kinetic studies for C–H insertion reactions using different substrates showed substantial differences in the rate of MPDA consumption, suggesting that carbene transfer is rate-limiting. Furthermore, primary kinetic isotope effects of 3.7 ± 0.3 and 2.7 ± 0.4 were measured using toluene and cyclohexane, respectively. These data are consistent with a mechanism that involves direct C–H in...

Metallophthalocyanines and metalloporphyrins as electrocatalysts: a case of hydrogen peroxide and glucose detection

This review summarizes the applications of metallophthalocyanine (MPc) and metallo-porphyrin (MP) complexes as electrocatalysts immobilized onto various electrodes for the detection of hydrogen peroxide and glucose. The uses of MPc and MP complexes as electron mediators for the detection of glucose at glucose oxidase modified surfaces are discussed.

Erratum to: Axial Imidazole Binding Strengths in Porphyrinoid Cobalt(III) Complexes as Studied by Tandem Mass Spectrometry

The Co(II) complexes of twelve meso-tetraaryl-porphyrins, -chlorins, and chlorin analogues containing non-pyrrolic heterocycles were synthesized and converted in situ to the corresponding Co(III) complexes coordinated to one or two imidazoles. Electrospray ionization tandem mass spectrometry (ESI-MS/MS) in conjunction with the energy-variable collision-induced dissociation (CID) technique was used to compare the relative gas-phase binding strength of the axially coordinated imidazoles to the octahedral and square planar Co(III) porphyrinoid complex ions. The observed binding energies of these ligands were rationalized in terms of the effects of porphyrinoid core structure and meso-substitution on the electron density on the central Co(III) centers. Some of these trends were supported by DFT-based computational studies. The study highlights to which extend porphyrins vary from chlorins and chlorin analogues in their coordination abilities and to which extraordinary degree meso-thienyl-substituents influence the electronic structure of porphyrins. The study also defines further the scope and limits CID experiments can be used to interrogate the electronic structures of metalloporphyrin complexes.