Effect of the nature of the tetrapyrrole macrocycle on the transmetallation of Zn2+ and Cd2+ porphyrins with PdCl2 in dimethylformamide

Transmetallation of zinc (Zn²⁺) and cadmium (Cd²⁺) complexes of 5,10,15,20-tetraphenylporphin, 5,10,15,20-tetra(4-chlorophenyl)porphyrin, 5,10,15,20-tetra(4-methoxyphenyl)porphyrin, tetrabenzoporphyrin, and octaphenyltetraazaporphyrin with PdCl₂ in DMF was studied by spectrophotometry. The influence of the nature of the tetrapyrrole macrocycle on the reactivity of Zn²⁺ porphyrins toward palladium chloride in boiling DMF was established. Palladium(II) complexes of 5,10,15,20-tetraphenylporphyrin, 5,10,15,20-tetra(4-chlorophenyl)porphyrin, 5,10,15,20-tetra(4-methoxyphenylporphyrin), and tetrabenzoporphyrin were prepared and identified.     

Substitution effects on the catalytic activity of Mn(III)-porphyrins in epoxidation of alkenes with iodosylbenzene: A comparison between the electron-rich and electron-deficient porphyrins

Oxidation of different olefins with iodosylbenzene in the presence of Mn(III) complexes of meso-tetra(para-tolyl)porphyrin, meso-tetra(ortho-tolyl)porphyrin, meso-tetra(thien-2-yl)porphyrin and β-hexaboromo-meso-tetra(thien-2-yl)porphyrin as catalyst has been studied. Oxidation of cis- and trans-stilbene in a competitive reaction strongly suggests the involvement of a high valent (porphyrin)MnO as the active oxidant intermediate, in the case of each catalyst. Clear observation of the band relevant to a (porphyrin)Mn(IV)O species in the presence of excess amounts of styrene shows the stability of this moiety towards reaction with olefins. Although, the stability of metalloporphyrins towards oxidative degradation decreases in the order MnT(o-tolyl)P(OAc) > MnT(thien-2-yl)PBr₆(OAc) > MnT(p-tolyl)P(OAc) ? MnT(thien-2-yl)P(OAc), a complex pattern of catalytic activity and product (epoxide) selectivity has been found for the Mn-porphyrins in oxidation of various alkenes.     

Spectral and photochemical properties of tetraphenylporphyrin tetrasulfonate supported on modified montmorillonite nanoparticles

A photocatalyst that effectively sensitizes the oxidation of 9,10-diphenylanthracene in toluene under irradiation with visible light has been prepared by the treatment of cationic surfactant-modified montmorillonite nanoparticles with a solution of meso-tetrakis(4-sulfonatophenyl)porphyrin. Reaction quantum yields and singlet oxygen generation probability have been determined. The shifts and intensity changes observed for the absorption bands of meso-tetrakis(4-sulfonatophenyl)porphyrin in the catalyst as compared with aqueous solutions are associated with solvation effects. The meso-tetrakis(4-sulfonatophenyl)porphyrin triplet state has been detected using the laser photolysis technique, and the rate constant of its quenching by oxygen on the surface of nanoparticles has been measured.     

Synthesis,crystal structure,and photoluminescence of a zinc metalloporphyrin

A zinc metalloporphyrin, ZnTCPP(acetone) (1) (TCPP = meso-tetra(4-carboxyphenyl)porphyrin), has been prepared via a solvothermal reaction and structurally characterized by single-crystal X-ray diffraction. Compound 1 features an isolated structure with a planar macrocycle and an embedded zinc ion binded to four pyrrole nitrogen atoms and one acetone oxygen atom. Photoluminescent investigation reveals that compound 1 displays an intensive emission in the red region.     

Structural investigations on diorgano- and triorganotin(IV) derivatives of [meso-tetra(4-sulfonatophenyl)porphine] metal chlorides

Several new complexes of organotin(IV) moieties with MCl_n[meso-tetra(4-sulfonatophenyl)porphine], (R₂Sn)₂MCl_n[meso-tetra(4-sulfonatophenyl)-porphinate]s and (R₃Sn)₄MCl_n [meso-tetra(4-sulfonatophenyl)porphinate]s, [M = Fe(III), Mn(III): n = 1, R = Me, n-Bu; Ph; M = Sn(IV): n = 2, R = Me, n-Bu] have been synthesized and their solid state configuration investigated by infrared (IR) and Mössbauer spectroscopy, and by ¹H and ¹³C NMR in D₂O.The electron density on the metal ion coordinated inside the porphyrin ring is not influenced by the organotin(IV) moieties bonded to the oxygen atoms of the side chain sulfonatophenyl groups, as it has been inferred on the basis of Mössbauer spectroscopy and, in particular, from the invariance of the isomer shift of the Fe(III) and Sn(IV) atoms coordinated into the porphyrin square plane of the newly synthesized complexes, with respect to the same atoms in the free ligand.As far as the coordination polyhedra around the peripheral tin atoms are concerned, infrared spectra and experimental Mössbauer data would suggest octahedral and trigonal bipyramidal environments around tin, in polymeric configurations obtained, respectively, in the diorganotin derivatives through chelating or bridging sulfonate groups coordinating in the square plane, and in triorganotin(IV) complexes through bridging sulfonate oxygen atoms in axial positions.The structures of the (Me₃Sn)₄Sn(IV)Cl₂[meso-tetra(4-sulfonatophenyl)porphinate] and of the two model systems, Me₃Sn(PS)(HPS) and Me₂Sn(PS)₂ [HPS = phenylsulfonic acid], have been studied by a two layer ONIOM method, using the hybrid DFT B3LYP functional for the higher layer, including the significant tin environment. This approach allowed us to support the structural hypotheses inferred by the IR and Mössbauer spectroscopy analysis and to obtain detailed geometrical information of the tin environment in the compounds investigated.¹H and ¹³C NMR data suggested retention of the geometry around the tin(IV) atom in D₂O solution.     

Synthesis of flexible dimeric meso-tetrakis-porphyrins

Monofunctionalisation of meso-tetrakis-porphyrins through introduction of a carboxylic group in the meso position of the phenyl group confers the necessary characteristics to anchor them through stable amide bonds to functionalised supports or to molecules. In this Letter we describe the synthesis, characterisation and photophysical evaluation of such a functionalised flexible dimeric porphyrin, bis-(meso-tetrakis-5,10,15-triphenyl-20-(p-carboxyphenyl)-porphyrinyl)-1,6-hexanediamide.     

Dissociation kinetics of cobalt and zinc β-octabromo-meso-tetraphenyl- and β-octaethyl-meso-tetraphenylporphyrin complexes

Kinetics of solvoprotolytic dissociation of zinc and cobalt porphyrin complexes with a porphyrin macrocycle distorted to different extents (β-octaethyl-meso-tetraphenylporphyrin and β-octabromo-meso-tetraphenylporphyrin) have been studied in binary proton-donating solvents. The main factor decreasing the stability of the porphyrin complexes is the distortion of the planar structure of the macrocycle. The reactivity of the cobalt porphyrins is governed by both structural and electronic effects.     

Synthesis of oligo(p-phenylene)-linked dyads containing free base, zinc(II) or thallium(III) porphyrins for studies in artificial photosynthesis

A series of (p-phenylene)_n-linked meso-mesityl-substituted porphyrin dyads (n=2-4) was prepared via Suzuki coupling of zinc(II) and free base porphyrin building blocks. The resulting zinc(II)/free base porphyrin dyads were demetalated. The series of free base porphyrin dimers (n=1-4), four other porphyrin dimers (with p-phenylene, diphenylethyne or diphenylbutadiyne linkers; and aryl or tridec-7-yl meso substituents), and several benchmark monomers were converted to the thallium(III)chloride complexes under mild conditions. The collection of eight Tl(III)Cl/Tl(III)Cl dimers is designed for studies of ground-state hole-transfer processes and comparison with the excited-state energy- and hole-transfer processes of the corresponding Zn(II)/free base dyads. Altogether, 18 new porphyrin arrays and benchmark monomers have been prepared.     

Regioselective sulfonation of 2-porphyrinylthiophene under kinetic and thermodynamic control

Sulfonation of meso-tetra(thien-2′-yl)porphyrin with concentrated sulfuric acid was found to produce several tetrasulfonated meso-tetra(thien-2′-yl)porphyrin isomers, where sulfonic acid groups were substituted at the 5- or the 4-positions of the thienyl groups, and the tetrasodium salts of the isomers were successfully isolated by reversed-phase HPLC. Temperature dependence of the production ratio of the isomers revealed that sulfonation reactions at the 5- and the 4-positions of 2-porphyrinylthiophene occur under kinetic and thermodynamic control, respectively.     

Structural parameters and vibrational spectra of a series of zinc meso-phenylporphyrins: A DFT and experimental study

The influences of meso-phenyl substitution on the geometric structure and vibrational spectra have been studied by DFT calculation (B3LYP/6-31G(d)) and experiment on a series of zinc porphyrins (ZnTPP: zinc 5,10,15,20-tetraphenylporphyrin; ZnTrPP: zinc 5,10,15-triphenylporphryin; ZnDPP: zinc 5,15-dipenylporphyirn; ZnMPP: zinc 5-monophenylporphyrin; ZnP: zinc porphine). Calculation indicates that meso-phenyl substitution gives rise to slight out-of-plane distortion but significant in-plane distortion, especially for the configuration around C_m atom, to zinc porphyrin. The assignment of experimental vibrational spectra was proposed mainly on the basis of calculation. Different shifting tendency upon meso-phenyl substitution is observed for different structure-sensitive bands, such as the shifting of ν₂, ν₃, ν₆, and ν₈ modes toward higher frequencies and ν₄ and ν₂₈ modes toward lower frequencies, upon meso-phenyl substitution. This is attributed primarily to in-plane nuclear reorganization effect (IPNR), though the contribution from out-of-plane distortion cannot be excluded completely. Analysis on vibrational structure reveals that asymmetric meso-phenyl substitution, especially the 5,15-diphenyl substitution of ZnDPP, brings about asymmetric vibrational displacement, or even splitting of vibrational structure to normal modes involving mainly the motion of meso-C_m. This is ascribed to the reduction of symmetry of porphyrin skeleton caused by asymmetric meso-phenyl substitution.     

MS/MS Fragmentation Behavior Study of meso-Phenylporphyrinoids Containing Nonpyrrolic Heterocycles and meso-Thienyl-Substituted Porphyrins

Free base and cobalt(II) complexes of six meso-tetraphenylporphyrinoids containing nonpyrrolic heterocycles and of three meso-thienylporphyrins were investigated using electrospray ionization tandem mass spectrometry (ESI-MS/MS). Their fragmentation was studied in a quadrupole ion trap as a function of the porphyrinoid macrocycle structure and compared with the fragmentation behavior of the benchmark compound meso-tetraphenylporphyrin. In situ oxidation of the neutral cobalt(II) complexes under ESI conditions produced singly charged cobalt(III) porphyrinoid ions; the free bases were ionized by protonation. For the porphyrinoids with an intact porphyrin core, the major fragmentation pathways observed were the losses of the meso-substituent (for meso-phenyl groups) and characteristic fragmentations of one or more meso-substituents (for the meso-thienyl group). Complex fragmentation pathways were observed for porphyrinoids with modifications to the porphyrin core but chemically reasonable structures could be assigned to most fragments, thus delineating general patterns for the behavior of pyrrole-modified porphyrins under CID conditions.

Novel mercury(II) complexes of meso-tetraphenylporphyrin and N-methylporphyrins

Treatment of meso-tetraphenylporphyrin, H₂TPP, with just over one equivalent of mercury(II) acetate in methylene chloride-THF gives mercury(II) meso-tetraphenylporphyrin, HgTPP. With excess of mercury(II) acetate, H₂TPP and HgTPP afford a novel dimetallic mononuclear porphyrin, AcOHgTPPHgOAc. In contrast, HgTPP reacts with mercury(II) chloride to give the chloro-analogue, ClHgTPPHgCl, but there is no reaction between H₂TPP and mercury(II) chloride. Demetallation of HgTPP in methylene chloride containing small amounts of hydrogen chloride proceeds via the dimetallic compound, ClHgTPPHgCl, to give free base HTPP. The reaction rate is dependent upon acid concentration suggesting that the rate determining step is protonation, but dilution causes no decrease in the rate; a mechanism which invokes the intermediacy of monohydrogen-meso-tetraphenylporphyrinatomercury(II) chloride, H(TPP)HgCl, in the formation of ClHgTPPHgCl and in its subsequent decomposition into H₂TPP, is proposed.N-Methylporphyrins react with mercury(II) acetate in methylene chloride-tetrahydrofuran to give the corresponding N-methylporphyrinatomercury(II) acetates, Me(P)HgOAc.     

Synthesis of three-dimensionally arranged porphyrin arrays via intramolecular meso-meso coupling

The synthesis and photophysical properties of three-dimensionally arranged porphyrin arrays with through-space electronic communication are reported. 1,3,5-Trioxamethylphenylene bridged Zn(II) porphyrin trimer 3 was coupled by Ag(I)-promoted oxidative coupling reaction to give porphyrin cage 5 comprising three meso-meso linked diporphyrins, which was then transformed by oxidation with DDQ and Sc(OTf)₃ into porphyrin cage 7 comprising three fused diporphyrins. Intramolecular meso-meso coupling reaction was applied to porphyrin pentamer 11 to provide porphyrin array 12 consisting of a porphyrin core flanked by two meso-meso linked diporphyrins. Further oxidation of 12 with DDQ and Sc(OTf)₃ afforded triply stacked porphyrin array 13 that is comprised of a porphyrin core flanked by two porphyrin tapes. UV-vis-NIR absorption and fluorescence spectra of 5, 7, 12, and 13 showed their distorted conformations and electronic interaction within the stacked porphyrin arrays.     

Handedness inversion of chiral mesoporous silica: A diffuse-reflectance circular dichroism study

Temperature-depended handedness inversion in chiral mesoporous silica was investigated by diffuse-reflectance circular dichroism spectra.     

Solar Driven Photocatalytic Activity of Porphyrin Sensitized TiO2: Experimental and Computational Studies

The absence of a secure long-term sustainable energy supply is recognized as a major worldwide technological challenge. The generation of H₂ through photocatalysis is an environmentally friendly alternative that can help solve the energy problem. Thus, the development of semiconductor materials that can absorb solar light is an attractive approach. TiO₂ has a wide bandgap that suffers from no activity in the visible spectrum, limiting its use of solar radiation. In this research, the semiconductor absorption profile was extended into the visible region of the solar spectrum by preparing porphyrin-TiO₂ (P-TiO₂) composites of meso-tetra(4-bromophenyl)porphyrin (PP1) and meso-tetra(5-bromo-2-thienyl)porphyrin (PP2) and their In(III), Zn(II) and Ga(III) metal complexes. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were performed on the porphyrins to gain insight into their electron injection capability. The results demonstrate that P-TiO₂ systems merit further in-depth study for applications that require efficient photocatalytic H₂ generation.     

The effect of chemical modification of the macrocycle on the complex formation between porphyrins and metal salts in organic solvents

The complex formation of β-octaethylporphyrin, β-octaethyl-meso-monophenylporphyrin, β-octaethyl-meso-tetraphenylporphyrin, meso-diphenylporphyrin, meso-triphenylporphyrin, and meso-tetraphenylporphyrin with Zn(II), Cu(II), Co(II), and Mn(II) acetates and chlorides in dimethylformamide, dimethylsulfoxide, pyridine, acetic acid, and a chloroform–methanol 1 : 1 mixture has been studied by means of spectrophotometry. The observed regulations are in line with the concept of chemical reactivity of the N–H bonds in porphyrins of different complexity.     

Tin(IV) porphyrin complexes with unsymmetrical axial ligation

Visible absorption and ¹H and ¹³C NMR spectra have been measured for some meso-tetraphenyl- and meso-tetra(p-tolyl)porphyrin complexes of tin(IV) containing axial hydroxo and formato ligands. The unsymmetrical hydroxo/formato complexes allow assessment of cis and trans influences on NMR chemical shifts and J(SnH) and J(SnC) values, confirming the strong donor properties of the OH ligand bound to six-coordinate tin(IV).     

meso -Tetrathienylporphyrins: Steady-state emission and structural properties

meso-Tetra (2′- and 3′-thienyl)porphyrins and their Zn(II)-complexes were examined by steady-state fluorescence measurements. These molecules exhibit significant bathochromic shift in their emission bands with decreased quantum yields relative to their correspondingmeso-tetraphenylporphyrin derivatives. The crystal structure of 5,10,15,20-tetrakis(3′-thienyl)porphinato zinc(II) shows planar and nonplanar stereochemical features of the macrocycle. One of the macrocycle shows nearly planar while the other exhibited predominantly saddle-shaped geometry. The extent of displacement of the Β-pyrrole carbons in the nonplanar (saddle) conformation is as high as ± 0·422 ?.     

Oligoether-strapped meso-pyrimidinylporphyrins

Bis(oligoether-strapped) zinc(II)-meso-pyrimidinylporphyrins were readily synthesized via nucleophilic aromatic substitution reactions of biscathechol-substituted tri- or tetraethylene glycol straps on the upper and lower faces of a Zn(II)-A₂B₂-meso-dichloropyrimidinylporphyrin precursor. The crown ether-like bridges surrounding the porphyrin core create peculiar cavities above and below the macrocyclic plane with appealing features for supramolecular host–guest chemistry.