Porphyrin Complexes Research Articles

The CO2 cycloaddition to epoxides and aziridines promoted by porphyrin-based catalysts

Thanks to its intrinsic eco–compatibility and high atom economy, the direct insertion of CO2 into three–membered rings, such as epoxides and aziridines, has become one of the most investigated strategies for the synthesis of cyclic carbonates and oxazolidin-2-ones. In this view, the following short account summarizes our recent results regarding the use of ruthenium porphyrin complexes and metal-free porphyrins, in combination with TBACl (tetrabutyl ammonium chloride), to promote the CO2 conversion into cyclic carbonates as well as N–alkyl and N-aryl oxazolidin-2-ones. Experimental data are described in combination with performed DFT studies that allowed proposing a reaction mechanism for the CO2 cycloaddition to aziridines promoted by metal-free porphyrins in which the adduct formed by TPPH2 and TBACl represents the real catalytic active species.

Synthesis, Characterization, DFT and Photocatalytic Studies of a New Pyrazine Cadmium(II) Tetrakis(4-methoxy-phenyl)-porphyrin Compound.

This study describes the synthesis, theoretical investigations, and photocatalytic degradational properties of a new (pyrazine)(meso-tetrakis(4-tert-methoxyphenyl)-porphyrinato)-cadmium (II) ([Cd(TMPP)-Pyz]) complex (1). The new penta-coordinated CdII porphyrin complex (1) was characterized by various spectroscopic techniques, including FT-IR, NMR, UV-visible absorption, fluorescence emission, and singlet oxygen, while its molecular structure was studied using single crystal X-ray diffraction. The UV–Vis spectroscopic study highlighted the redshift of the absorption bands after the insertion of the Cd(II) metal ion into the TMPP ring. The co-coordination of the pyrazine axial ligand enhanced this effect. A fluorescence emission spectroscopic study showed a significant blueshift in the Q bands, accompanied by a decrease in the fluorescence emission intensity and quantum yields of Φf = 0.084, Φf = 0.06 and Φf = 0.03 for H2-TMPP free-base porphyrin, [Cd(TMPP)] and [Cd(TMPP)(Pyz)] (1) respectively. Singlet oxygen revealed that the H2-TMPP porphyrin produced the most efficient singlet oxygen quantum yield of (ΦΔ = 0.73) compared to [CdTMPP] (ΦΔ = 0.57) and [Cd(TMPP)(Pyz)] (1) (ΦΔ = 0.13). In the crystal lattice, the [Cd(TMPP)Pyz] was stabilized through non-covalent intermolecular interactions (NCI), such as the hydrogen bonds C-H···N and C-H···Cg. Additionally, crystal explorer software was then utilized to measure the quantitative analysis of the intermolecular interactions in the unit cell of the crystal structure and established that the C-H···π interaction dominated. The Natural bond orbital (NBO) analysis revealed that each molecule is stabilized by hyperconjugation and charge delocalization. As a photocatalyst, the coordination complex 1 showed excellent photocatalytic activity toward the degradation of Levafix Blue CA reactive dye (i.e., dye photo-degradation of 80%).

Synthesis of a donor–acceptor heterodimer via trifunctional completive self-sorting

Selective self-assembly of heterodimers consisting of two non-identical subunits plays important roles in Nature but is rarely encountered in synthetic supramolecular systems. Here we show that photocleavage of a donor–acceptor porphyrin complex produces an heterodimeric structure with surprising selectivity. The system forms via a multi-step sequence that starts with an oxidative ring opening, which produces an equimolar mixture of two isomeric degradation products (zinc(II) bilatrien-abc-ones, BTOs). These two isomers are susceptible to water addition, yielding the corresponding zinc(II) 15-hydroxybiladien-ab-ones (HBDOs). However, in the photocleavage experiment only one HBDO isomer is formed, and it quantitatively combines with the remaining BTO isomer. The resulting heterodimer is stabilized by a Zn–O coordination bond and extended dispersion interactions between the overlapping π-surfaces of the monomers. The observed selectivity can be seen as a case of completive self-sorting, simultaneously controlled by three types of complementary interactions.

Efficient Integral-Direct Methods for Self-Consistent Reduced Density Matrix Functional Theory Calculations on Central and Graphics Processing Units

Reduced density matrix functional theory (RDMFT), a promising direction in the problem of describing strongly correlated systems, is currently limited by its explicit dependence on natural orbitals and, by extension, the costly need to construct two-electron integrals in the molecular orbital basis. While a resolution-of-the-identity approach can reduce the asymptotic scaling behavior from O(N5) to O(N4), this is still prohibitively expensive for large systems, especially considering the usually slow convergence and the resulting high number of orbital optimization steps. In this work, efficient integral-direct methods are derived and benchmarked for various approximate functionals. Furthermore, we show how these integral-direct methods can be integrated into existing self-consistent energy minimization frameworks in an efficient manner, including improved methods for calculating diagonal elements of the two-electron integral tensor as required in self-interaction-corrected functionals and second derivatives of the energy with respect to the occupation numbers. In combination, these methods provide speedups of up to several orders of magnitude while greatly diminishing memory requirements, enabling the application of RDMFT to large molecular systems of general chemical interest, such as the challenging triplet-quintet gap of the iron(II) porphyrin complex.

Efficient Reductive Defluorination of Branched PFOS by Metal-Porphyrin Complexes.

Vitamin B12 (VB12) has been reported to degrade PFOS in the presence of TiIII citrate at 70 °C. Porphyrin-based catalysts have emerged as VB12 analogues and have been successfully used in various fields of research due to their interesting structural and electronic properties. However, there is inadequate information on the use of these porphyrin-based metal complexes in the defluorination of PFOS. We have therefore explored a series of porphyrin-based metal complexes for the degradation of PFOS. CoII-5,10,15,20-tetraphenyl-21H,23H-porphyrin (CoII-TPP), CoII-5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphyrin (CoII-M-TPP), and CoIII-M-TPP exhibited efficient reductive defluorination of the branched PFOS. Within 5-8 h, these compounds achieved the same level of PFOS defluorination as VB12 achieved in 7-10 days. For branched isomers, the specific removal rate of the CoII-TPP-TiIII citrate system is 64-105 times higher than that for VB12-TiIII citrate. Moreover, the CoII-TPP-TiIII citrate system displayed efficient (51%) defluorination for the branched PFOS (br-PFOS) in 1 day even at room temperature (25 °C). The effects of the iron and cobalt metal centers, reaction pH, and several reductants (NaBH4, nanosized zerovalent zinc (nZn0), and TiIII citrate) were systematically investigated. Based on the analysis of the products and previously published reports, a new possible defluorination pathway of branched PFOS is also proposed.

Meso-carbazole substituted porphyrin complexes: Synthesis and spectral properties according to experiment, DFT calculations and the prediction by machine learning methods

In this work, two porphyrins bearing [3,6-di-tert-butyl-carbazol-9-yl-benzoyloxy)]- (1) and [3,6-bis(3′,6′-di(tert-butyl)-9′H-carbazol)-9H-carbazolbenzoyloxy]phenyl (2) groups and their zinc (1Zn, 2Zn)/cobalt (1Co, 2Co) complexes were synthesized and studied by experimental and theoretical methods. The spectral parameters (UV–vis absorption/femtosecond transient absorption/fluorescence, IR, 1H NMR, mass spectra) of the compounds were observed. Their structure was also examined by the DFT method. The comparative study of the UV–vis spectra by the DFT/TDDFT calculation, and by the prediction of the Soret band maximum using machine learning methods, namely the consensus models based on the data of over 10000 porphyrin free bases and their complexes with metals was performed. The absorption maximum wavelength (Soret band) of porphyrins predicted with machine learning methods showed better agreement with the experimental data compared to the DFT/TDDFT calculation. The final consensus model is freely available at https://ochem.eu/article/145340 and can be used by the other researchers to obtain new functionalized porphyrins with desired optical properties.

Design and Study of Water-Soluble Chemically Conjugated Complexes of Porphyrins with Cyclosaccharides

Design and Study of Water-Soluble Chemically Conjugated Complexes of Porphyrins with Cyclosaccharides

Structural characterization of the water-soluble porphyrin complexes [FeII(TPPS) (NO•)]4─ and [μ-O-([FeIII(TPPS)])2]8─

Iron water-soluble porphyrins have been long used as biomimetic compounds for modelling the active sites found in heme-enzymes. In this regard, the anionic porphyrin [FeIII(TPPS)]3─ and its coordination complexes have been repeatedly chosen as suitable water-soluble platforms for bioinorganic chemistry studies. In this work we report for the first time the crystal structure of the water-soluble nitrosyl complex [FeII(TPPS) (NO•)]4─ along with that of oxodimeric ferric species [μ-O-([FeIII(TPPS)])2]8─.

Chemical, Thermal, and Radiation Resistance of an Iron Porphyrin: A Model Study of Biosignature Stability.

Metal complexes of porphyrins and porphyrin-type compounds are ubiquitous in all three domains of life, with hemes and chlorophylls being the best-known examples. Their diagenetic transformation products are found as geoporphyrins, in which the characteristic porphyrin core structure is retained and which can be up to 1.1 billion years old. Because of this, and their relative ease of detection, metalloporphyrins appear attractive as chemical biosignatures in the search for extraterrestrial life. In this study, we investigated the stability of solid chlorido(2,3,7,8,12,13,17,18-octaethylporphyrinato)iron(III) [FeCl(oep)], which served as a model for heme-like molecules and iron geoporphyrins. [FeCl(oep)] was exposed to a variety of astrobiologically relevant extreme conditions, namely: aqueous acids and bases, oxidants, heat, and radiation. Key results are: (1) the [Fe(oep)]+ core is stable over the pH range 0.0–13.5 even at 80°C; (2) the oxidizing power follows the order ClO− > H2O2 > ClO3− > HNO3 > ClO4−; (3) in an inert atmosphere, the iron porphyrin is thermally stable to near 250°C; (4) at high temperatures, carbon dioxide gas is not inert but acts as an oxidant, forming carbon monoxide; (5) a decomposition layer is formed on ultraviolet irradiation and protects the [FeCl(oep)] underneath; (6) an NaCl/NaHCO3 salt mixture has a protective effect against X-rays; and (7) no such effect is observed when [FeCl(oep)] is exposed to iron ion particle radiation. The relevance to potential iron porphyrin biosignatures on Mars, Europa, and Enceladus is discussed.

Electrochemical Studies on Manganese (III) Complex with meso-5, 10, 15, 20-Tetrakis (o-nitrophenyl) porphyrin by Cyclic Voltammetry and UV-Visible Spectrophotometry

Meso-5,10,15,20-Tetrakis(o-nitrophenyl)porphyrin, [T (o-NO2)PP] and manganese (III) meso-5,10,15,20- Tetrakis(2,5-dimethoxyphenyl)porphyrin, Mn[T(o- NO2)PP] have been prepared. The Mn[T(o-NO2)PP] complex is characterized by UV-Vis spectrophotometric and cyclic voltametric (CV) studies. The preparation of Mn(III) porphyrin complex may be attributed due to a significant metal-porphyrin π interaction. In Mn(III) porphyrin, Mn is in a high spin d4 configuration with octahedral geometry. Mn(III) porphyrin geometry has been altered to square pyramidal Mn(II) porphyrin after addition of ethylamine. In square pyramidal Mn(II) porphyrin, Mn atom is in a high-spin d5 configuration with the occupied d(x 2 - y 2 ) orbital whose orbital energy is low. This shows that Mn(III) will be out of the plane of porphyrin. Successive addition of diethylamine, Mn(III) porphyrin geometry has been changed to tetragonal complex due to a weak π back bonding. It appears that π -bonding is lowered when the tetragonal complexes are formed. This might arise due to the expansion of the in-plane metal to porphyrin in a direction to occupy two axial ligands of ethylamine. The geometry changes indicate that the two ethyl amines groups occupy 5th and 6th places as axial coordination site due to the availability of two ethylamine from ethyl, diethyl and triethyl amines. Cyclic voltammogram confirmed the oxidation state and reduction behavior of Mn porphyrin complex.

Mechanistic Studies on the Epoxidation of Alkenes by Macrocyclic Manganese Porphyrin Catalysts.

Macrocyclic metal porphyrin complexes can act as shape‐selective catalysts mimicking the action of enzymes. To achieve enzyme‐like reactivity, a mechanistic understanding of the reaction at the molecular level is needed. We report a mechanistic study of alkene epoxidation by the oxidant iodosylbenzene, mediated by an achiral and a chiral manganese(V)oxo porphyrin cage complex. Both complexes convert a great variety of alkenes into epoxides in yields varying between 20–88 %. We monitored the process of the formation of the manganese(V)oxo complexes by oxygen transfer from iodosylbenzene to manganese(III) complexes and their reactivity by ion mobility mass spectrometry. The results show that in the case of the achiral cage complex the initial iodosylbenzene adduct is formed on the inside of the cage and in the case of the chiral one on the outside of the cage. Its decomposition leads to a manganese complex with the oxo ligand on either the inside or outside of the cage. These experimental results are confirmed by DFT calculations. The oxo ligand on the outside of the cage reacts faster with a substrate molecule than the oxo ligand on the inside. The results indicate how the catalytic activity of the macrocyclic porphyrin complex can be tuned and explain why the chiral porphyrin complex does not catalyze the enantioselective epoxidation of alkenes.

Unity Makes Strength: Constructing Polymeric Catalyst for Selective Synthesis of CO 2 /Epoxide Copolymer

Unity Makes Strength: Constructing Polymeric Catalyst for Selective Synthesis of CO ₂ /Epoxide Copolymer

The effect of charge on Zn tetra morpholine porphyrin conjugated to folic acid-nitrogen doped graphene quantum dots for photodynamic therapy studies

Zinc tetra morpholine porphyrin (complex 2), and its quaternized derivative (complex 3) were synthesized and conjugated to folic acid decorated nitrogen doped graphene quantum dots (FA-NGQDs) through π−π stacking to study their photodynamic therapy (PDT) efficacy. Photophysiochemical properties of complexes 2, 3, and their conjugates (2-FA-NGQDs, 3-FA-NGQDs) were studied. It was found that complex 3 had higher ϕΔ of 0.56 compared to complex 2 with ϕΔ of 0.24, and respective composites: 3-FA-NGQDs had higher ϕΔ compared to 2-FA-NGQDs. The PDT studies were conducted for nanoparticles (FA-NGQDs), complexes (2, 3), and respective composites (2-FA-NGQDs, and 3-FA-NGQDs) using MCF-7 breast cancer cell. Dark toxicity of all compounds was above 90% which is negligible. At a highest concentration of 40 µg/mL, 3-FA-NGQDs gave the lowest cell viability of 28% compared to all other conjugates and porphyrins alone.

Photodynamic activity of novel cationic porphyrins conjugated to graphene quantum dots against Staphylococcus aureus

Novel 5-(pyridyl)-10-15-20-tris(4-bromophenyl) porphyrin (complex 1), indium metal derivative (complex 2), and quaternized derivative (complex 3) were synthesized and conjugated to graphene quantum dots (GQDs). The conjugation of the porphyrins to GQDs was through [Formula: see text]-[Formula: see text] stacking. Herein, the [Formula: see text]-[Formula: see text] stacking approach was used to avoid covalent conjugation which might compromise the intrinsic chemical and physical properties. The photodynamic activities of the proposed nanomaterials were assessed towards Staphylococcus aureus cell obliteration. The photophysical properties of the prepared complexes were also studied prior to the application. Moreover, a decrease in fluorescence lifetimes was observed upon metalation of complex 1. As anticipated, singlet oxygen quantum yield ([Formula: see text] increased notably upon heavy metal (indium) insertion and upon composite formation. Antimicrobial photodynamic therapy comparative studies were done on quaternized and unquaternized indium porphyrins conjugated to GQDs. Complex 3-GQDs exhibited the highest antibacterial activities compared to other complexes, and this was attributed to the high [Formula: see text] which plays an imperative role in photodynamic therapy applications.

Computational study of ground-state properties of μ2 -bridged group 14 porphyrinic sandwich complexes.

The structural properties of μ2 -bridged porphyrinic double-decker complexes are investigated and the influence of various ligands, metals, substituents, and bridging atoms on the dominant structural motif is elucidated. A variety of quantum chemical methods including semiempirical (SQM) methods and density functional theory (DFT) is assessed for the calculation of ecliptic and staggered conformational energies. Local coupled cluster (DLPNO-CCSD(T1)) data are generated for reference. The r2 SCAN-3c composite scheme as well as the B2PLYP-D4/def2-QZVPP approach are identified as reliable methods. Energy decomposition analyses (EDA) and localized molecular orbital analyses (LMO) are used to investigate the bonding situation and the nature of the inter-ligand interaction energy underlining the crucial role of attractive London dispersion interactions. Targeted modification of the bridging atom, e.g., by replacing O2- by S2- is shown to drastically change the major structural features of the investigated complexes. Further, the influence of different substituents of varying size at the phthalocyanine ligand regarding the dominant conformation is described.

Synthesis of zinc porphyrin complex for improving mechanical, UV-resistance, thermal stability and fire safety properties of polystyrene

Polystyrene (PS) is one of the most commonly used general plastics. Nonetheless, PS is greatly limited by its inherent disadvantages such as high flammability, low stability and brittleness. To address these issues, 5,10,15,20-tetrakis(4-bromophenyl) porphyrin (TBPP) and zinc 5,10,15,20-tetrakis(4-bromophenyl) porphyrin (Zn-TBPP) were synthesized as multifunctional additives for fabricating high-performance PS composites. Both TBPP and Zn-TBPP showed high thermal stability and excellent UV-absorption, which significantly enhanced the UV-resistance of PS without sacrificing mechanical property after 100 h UV-aging. The addition of 5 wt% Zn-TBPP led to the remarkable improvement of thermal stability of PS (41 °C and 79 °C increases in the thermal decomposition temperature at 5 wt% mass loss under N2 and air, respectively). Moreover, contributed from the strong π-π interaction between porphyrins and PS chains, the mechanical properties of PS were enhanced when 5 wt% Zn-TBPP was added into PS (11.1% increase in tensile strength and 96.6% increase in elongation at break). Furthermore, compared to TBPP/PS, Zn-TBPP/PS exhibited an improved flame retardant performance with 26.0%, 14.4% and 31.5% reduction of peak heat release rate, peak CO and CO2 production respectively, indicating the catalytic flame retardant effect from zinc element.

Electrocatalytic CO2 Reduction: from Discrete Molecular Catalysts to Their Integrated Catalytic Materials.

Molecular catalysts (metal complexes), with molecularly defined uniform active sites and atomically precise structural tailorability allowing for regulating catalytic performance through metal- and ligand-centered engineering and elucidating reaction mechanisms via routine photoelectrochemical characterizations, have been increasingly explored for electrocatalytic CO2 reduction (ECR). However, their poor stability and low catalytic current density are undesirable for practical applications. Heterogenizing discrete molecular catalysts can potentially surmount these issues, and the resulting integrated catalysts largely share catalytical properties with their discrete molecular counterparts, which bridge the gap between heterogeneous and homogeneous catalysis and combine their advantages. This minireview surveys advances in design and regulation of molecular catalysts such as porphyrin, phthalocyanine, and bipyridine-based metal complexes and their integrated catalytic materials for selective ECR.

Stability of Fe(III) and Sn(IV) Metalloporphyrins Adsorbed on Cation-Exchanged Montmorillonite

The iron(III)tetraphenylporphyrin chloride Fe(III)TPPCl, iron(III)tetra-naphthylporphyrin Fe(III)TNPCl, μ-oxo-bis[tetraphenylporphyriniron(III)] [(Fe(III)TPP)2O], μ-oxo-bis[tetranaphthylporphyriniron(III)] [(Fe(III)TNP)2O], tin(IV)tetraphenylporphyrin chloride Sn(IV)TPPCl2 and tin(IV)tetra-naphthylporphyrin Sn(IV)TNPCl2 complexes were all found to be adsorbed onto the montmorillonite MMT clay without demetallation. The evidence from the visible absorption and diffuse reflectance spectra all showed that the species present on the montmorillonite are the metallated form. Also the evidence from Mossbauer spectroscopy confirm these findings. The only process that occurs is that the dimeric form of the iron complexes underwent transformation to the monomeric form. The clay-complex systems were characterized using visible absorption spectra, diffuse reflectance spectra, X-ray diffraction, Mossbauer spectra and Electron microscopy.
 HIGHLIGHTS
 
 Fe(III)TPPCl, Fe(III)TNPCl, Sn(IV)TPPCl2, and Sn(IV)TNPCl2 porphyrin complexes adsorbed onto the montmorillonite clay without demetallation
 The dimeric forms of iron porphyrin complexes [(Fe(III)TPP)2O] and [(Fe(III)TNP)2O are converted to the monomeric form when adsorbed on montmorillonite clay
 The weak acidity of montmorillonite clay does not have the ability to cause demetallation of the metallo complexes of porphyrin

Environment-Friendly Catalytic Mineralization of Phenol and Chlorophenols with Cu- and Fe- Tetrakis(4-aminophenyl)-porphyrin—Silica Hybrid Aerogels

Fenton reactions with metal complexes of substituted porphyrins and hydrogen peroxide are useful tools for the mineralization of environmentally dangerous substances. In the homogeneous phase, autooxidation of the prophyrin ring may also occur. Covalent binding of porphyrins to a solid support may increase the lifetime of the catalysts and might change its activity. In this study, highly water-insoluble copper and iron complexes of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin were synthesized and bonded covalently to a very hydrophilic silica aerogel matrix prepared by co-gelation of the propyl triethoxysilyl-functionalized porphyrin complex precursors with tetramethoxysilane, followed by a supercritical carbon dioxide drying. In contrast to the insoluble nature of the porphyrin complexes, the as-prepared aerogel catalysts were highly compatible with the aqueous phase. Their catalytic activities were tested in the mineralization reaction of phenol, 3-chlorophenol, and 2,4-dichlorophenol with hydrogen peroxide. The results show that both aerogels catalyzed the oxidation of phenol and chlorophenols to harmless short-chained carboxylic acids under neutral conditions. In batch experiments, and also in a miniature continuous-flow tubular reactor, the aerogel catalysts gradually reduced their activity, due to the slow oxidation of the porphyrin ring. However, the rate and extent of the degradation was moderate and did not exclude the possibility that the as-prepared catalysts, as well as their more stable derivatives, might find practical applications in environment protection.

Two novel pyrazine Zn(II)-porphyrins complexes: Synthesis, photophysical properties, structure study, DFT-Calculation and assessment of an azo dye removal from aqueous solution

In the current work, two new zinc-porphyrinic complexes bearing pyrazine as axial ligand, i.e. (pyrazine)(meso-tetrakis-(4-phenoxyphenyl)porphyrinato)zinc(II) [Zn(TBOPP)(pyz)] (1) and (aqua)(pyrazine)(meso-tetrakis(3,4,5-trimethoxyphenyl)porphyrinato)zinc(II) monohydrate [Zn(TTMP)(pyz)(H2O)].H2O (2) were successfully synthesized. New complexes were extensively characterized using elemental analysis, 1H NMR, UV–visible, single-crystal X-ray, and mass spectrometry (ESI) techniques. Single crystal X-ray studies revealed penta-coordinated environment around each Zn(II) metal in complexes with pyrazine as an axial ligand. The complexes were stabilized by weak C–H … Cg π intermolecular interactions involving pyridyl, phenyl and pyrrole centroid rings. Optical absorption studies confirmed the medium band gap and semiconducting nature of the compounds. Emission studies indicated that the axial ligand has no significant effect on the fluorescence quantum yields (ɸf) and the lifetime (τf) values. The ability of calmagite dye (an anionic dye) to remove the free bases and the Zn(II) complexes from aqueous solution has also been presented. Frontier molecular orbital (HOMO-LUMO) energies for H2TBOPP, H2TTMP, [Zn(TBOPP)] and [Zn(TTMP)] with calmagite were determined using density functional theory (DFT) calculation showing the charge transfer within the molecule.