The NMR spectra of the porphyrins 16—zinc(II) meso-tetraphenylporphyrin (Zn TPP) as a diamagnetic shift reagent. A quantitative ring current model

The facile preparation of zinc(II) meso-tetraphenylporphyrin (Zn TPP) and derivatives from substituted benzaldehydes and pyrrole, combined with the calculation of ring current shifts in these molecules, provides a useful series of selective diamagnetic shift reagents. The porphyrin-ligand equilibrium is examined for some nitrogenous bases and the complexation shifts (δP values) are obtained in precisely the same manner as LIS. The parameterization of the double-dipole model of the porphyrin ring current is given, with the inclusion of the phenyl ring currents and free rotation about the substrate-Zn bond. Precise agreement with the porphyrin proton chemical shifts and the complexation shifts of the geometrically rigid substrates of pyridine, 4-picoline and quinuclidine is obtained. In contrast, the ¹³C complexation shifts in these molecules are subject to additional effects other than the ring current shift.     

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.     

Electronic and steric effects of substituents on the coordinating properties of porphyrins

Kinetics of the formation of zinc complexes of porphyrin with various substituents was studied in acetic acid and pyridine. The introduction of strong electron-withdrawing substituents (nitro groups) to the meso-positions of the porphyrin macrocycle was shown to change the reaction rate by an order of magnitude or less compared to the phenyl-substituted analogs. However, the introduction of a large number of bulky substituents leads to the deformation of the porphyrin ligand and thus affects much stronger the coordination properties of porphyrins, decreasing or increasing the rate of the complexation reaction by several orders of magnitude.     

Porphyrin system containing [2.2]paracyclophane units

Meso-tetrakis([2.2]paracyclophanyl)porphyrin was obtained from [2.2]paracyclophanecarbaldehyde and pyrrole. Replacement of phenyl groups in meso-tetraphenylporphyrin by paracyclophanyl substituents remarkably influences the electronic structure of the molecule, causing bathochromic shifts of all uv-vis absorption bands, and changing the ring current of the porphyrin core. The shifts in the electron spectrum are substantially greater than those observed for other porphyrin derivatives characterized by their extended π-electron systems, such as meso-tetrakis(2-phenylethenyl)porphyrin and meso-tetrakisbiphenylporphyrin.     

Regularities of Extra Coordination of Nitrogen-containing Ligands with an Anthracenyl-capped Zinc Porphyrin

3,3'-Dibutyl-4,4'-dimethylpyrrolylmethane was reacted with 9,10-bis(2-formylphenyloxymethyl)anthracene to synthesize a capped porphyrin, and its zinc complex was prepared. The coordination properties of the capped zinc porphyrin in extra coordination with N-methylimidazole, imidazole, pyridine, 3,5-dimethylpyrazole, and dimethylformamide in o-xylene were studied. A correlation of the stability of the extra complexes and the basicity of the extra ligands was established. A correlation between the stability of the extra complexes and the shifts of their principal electronic absorption bands with respect to those of the zinc porphyrin was found. Deformations of the porphyrin ligand were noted to affect the strengyh of the metalextra ligand bond. The geometric and energetic characteristics of the fivecoordinate zinc porphyrin were obtained by quantum-chemical calculations. A correlation between the calculated energy of interaction of the central metal atom with the nitrogen atom of the extra ligand and the stability of the extra complexes of the capped Zn porphyrin was revealed.     

Oxidation of pyridines with copper sulfate

Oxidation of pyridine, 3-picoline, 3,5-lutidine, quinoline, isoquinoline and acridine with hydrated copper sulfate at high temperatures gives the corresponding pyridones, possibly via the intramolecular reaction of a base - Cu(II) complex. Overall conversions are rather poor. 2- And 4-picolines and their methyl homologues undergo some demethylation under these conditions and some picolinic acid is isolated from 2-picoline. 2- And 4-ethylpyridines give both pyridine and 2- and 4-picoline, respectively.     

Heterogeneous reactions of solid nickel(II) complexes,III

The thermal decompositions of solid complexes of the type Ni(NCS)₂L₂ (L = pyridine,α-picoline,β-picoline, 2,6-lutidine, and quinoline) were studied by means of the derivatograph. It was found that the decompositions of complexes with pyridine,α-picoline, 2,6-lutidine, and quinoline (the pseudo-octahedral complex) are onestep processes, and those of complexes withβ-picoline and quinoline (the squareplanar complex) consist of two steps. Diffuse reflectance spectra were recorded to elucidate the structures of the decomposition intermediates. The reasons for the different stoichiometries of decomposition for complexes of the same type are discussed.     

A Porphyrin Iron(III) π-Dication Species and its Relevance in Catalyst Design for the Umpolung of Nucleophiles

Isoporphyrins have recently been identified as remarkable species capable of turning the nucleophile attached to the porphyrin ring into an electrophile, thereby providing umpolung of reactivity (Inorg. Chem. 2022 , 61, 8105–8111). They are generated by nucleophilic attack on an iron(III) π-dication, a class of species that has received scant attention. Here, we explore the effect of the porphyrin meso-substituent and report a iron(III) π-dication bearing the meso-tetraphenylporphyrin (TPP) ligand. We provide an extensive study of the species by UV/Vis absorption, ²H NMR, EPR, applied field Mössbauer, and resonance Raman spectroscopy. We further explore the system's highly dynamic and tunable properties and address the nature of the axial ligands as well as the conformation of the porphyrin ring. The insights presented are essential for the rational design of catalysts for the umpolung of nucleophiles. Such catalytic avenues could for example provide a novel method for electrophilic chlorinations. We further examine the importance of electronic tuning of the porphyrin by nature of the meso-substituent as a factor in catalyst design.     

Antibacterial photoactivity and photosensitized oxidation of phenols with meso-tetra-(4-benzoate, 9-phenanthryl)-porphyrin and its metal complexes (Zn and Cu)

We performed the synthesis and characterization of meso-tetra-(4-benzoate-9-phenanthryl)-porphyrin and its Zn and Cu complexes. Synthesis of meso-tetra-(4-benzoate-9-phenanthryl)-porphyrin was carried out by dry gaseous HCl, meso-tetra-(4-carboxyphenyl)-porphyrin, and 9-phenantrol in tetrahydrofuran. The preparation of metal complexes was carried out using the method of the acetates. All porphyrins were characterized by FT-IR, NMR (¹H and ¹³C), MS, UV–visible, and fluorescence spectroscopy. Their photophysical properties: photostability, fluorescence quantum yields, energy transfer, and generation of singlet oxygen were determined and compared with the meso-tetraphenylporphyrin. Photochemical studies on their effectiveness as photosensitizers were performed through photo-oxidation of alcohols, phenol, and 2-naphthol. Higher efficiency of degradation was obtained with photostable TB9FPCu. The antibacterial photoactivity assay was tested against Escherichia coli and its viability was measured by chemiluminescence. The highest inactivation levels were obtained by ester TB9FP and Zn complex. The properties of the photosensitizer and its efficiency vary as a result of modifying its structure. The results obtained show that the efficiency of a photosensitizer depends on multiple factors. Thus, we can say that the copper complex is efficient in degradation of alcohol, while the metal-free porphyrin is better for antibacterial applications.     

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.     

Studies of porphyrin zinc compounds intercalated into V<Subscript>2</Subscript>O<Subscript>5</Subscript> xerogel

The intercalation of meso-tetrakis(4-pyridyl)porphyrin zinc, the cationic salts of meso-tetrakis(N-methylpyridinium-4-yl)porphyrin zinc, and zwitterionic meso-tetrakis-[N-(3-sulfonatopropyl)pyridinium-4-yl]porphyrin zinc from aqueous solutions as well as of meso-tetrakis(N-methylpyriclinium-4-yl)porphyrin zinc from pyridine solutions into V₂O₅ xerogel was studied. The intercalation complexes obtained were characterized by X-ray diffraction analysis, TG analysis, IR, and UV reflectance spectroscopy.     

One-pot synthesis of furo[2,3-h]quinoline and furo[2,3-h]isoquinoline derivatives using Fischer carbene complex

A new route for the synthesis of furo[2,3-h]quinoline and furo[2,3-h]isoquinoline derivatives have been explored through the coupling of carbene complexes with pyridine-bridged enynes. This reaction process, involving the annulation of both furan and benzene ring on to a pre-existing pyridine ring is highly efficient in the presence of triphenylphosphine as ligand additive.     

Chromium(III) and Chromium(IV) Tetraphenylporphine Complexes

Stable chromium complex (AcO)CrTPP was synthesized through the reaction of meso-tetraphenylporphine with chromium(III) acetate in boiling phenol. Coordination properties of chromium porphyrin in reaction with imidazole and pyridine in o-xylene were studied by electronic absorption spectroscopy and computer modeling. A single-electron oxidation of chromium(III) complex was found to be affected by peroxide compounds. The stability of an extra complex depends on the basic properties of the extra ligand and oxidation number of the central metal atom. The complex stability correlates with the calculated energy of formation of the metal–extra ligand bond. The geometrical structure and energy parameters of hexacoordinated chromium porphyrins were calculated using the quantum-chemical method. The effect of the cis and trans position of ligands in the composition of a macrocyclic compound was established to be significant only in the extra complexes (AcO)CrTPP.     

Quaternary salts of some heterocycles containing nitrogen

A series of mono- and biquaternary salts were synthesized from 1, 3-dichloropropane-2-ol and the nitrogen-containing heterocycles quinoline, isoquinoline, quinaldine, pyridine, 2-picoline, and lepidine. The UV-spectra of the compounds obtained were investigated.     

Calcium Hydride Catalyzed Highly 1,2‐Selective Pyridine Hydrosilylation

Reaction of the calcium hydride complex (DIPPnacnac‐CaH?THF)₂ with pyridine is much faster and selective than that of the corresponding magnesium hydride complex (DIPPnacnac = [(2,6‐iPr₂C₆H₃)NC(Me)]₂CH). With a range of pyridine, picoline and quinoline substrates, exclusive transfer of the hydride ligand to the 2‐position is observed and also at higher temperatures no 1,2→1,4 isomerization is found. The heteroleptic product DIPPnacnac‐Ca(1,2‐dihydropyridide)?(pyridine) shows fast ligand exchange into homoleptic calcium complexes and therefore could not be isolated. Calcium hydride reduction of isoquinoline gave well‐defined homoleptic products which could be characterized by X‐ray diffraction: Ca(1,2‐dihydroisoquinolide)₂?(isoquinoline)₄ and Ca₃(1,2‐dihydroisoquinolide)₆?(isoquinoline)₆. The striking selectivity difference in the dearomatization of pyridines by Mg or Ca complexes could be explained by DFT theory and was utilized in catalysis. Whereas hydroboration of pyridine with pinacol borane with a calcium hydride catalyst gave only minor conversion, the hydrosilylation of pyridine and quinolines with PhSiH₃ yields exclusively 1,2‐dihydropyridine and 1,2‐dihydroquinoline silanes with 80–90 % conversion. Similar results can be achieved with the catalyst Ca[N(SiMe₃)₂]₂?(THF)₂. These calcium complexes represent the first catalysts for the 1,2‐selective hydrosilylation of pyridines.     

Crystal solvates of carboxy-substituted Zn(II) phthalocyaninates with pyridine

Physicochemical characteristics (composition, energetic and chemical stability) of the molecular complexes of carboxy-substituted Zn(II) phthalocyaninates with pyridine were determined. It was found that the carboxyl substituents in positions 4 and 5 of the complex Zn(4,5-COOH)₈Pc favor the formation of the most stable molecular complexes with pyridine. The carboxyl substituents in the composition of Zn(3-COOH)₄Pc are not solvated with pyridine due to steric hindrances and the formation of the hydrogen bond between the carboxyl H atom and the meso-nitrogen atom; the molecular complexes of a tetrasubstituted Zn(4-COOH)₄Pc with pyridine are unstable.     

Energies of Charge Transfer for the Supramolecular Complexes of [60]- and [70]Fullerenes with a Series of meso-Tetraphenylporphyrins in the Solution State

Supramolecular complexes of [60]- and [70]fullerenes with various meso-tetraphenylporphyrins in toluene solutions have been studied by electronic absorption spectroscopy. Charge transfer (CT) absorption bands are observed in the visible region. Vertical ionization potentials (I _D ^V) of the meso-tetraphenylporphyrins are reported from a study of EDA interaction of these porphyrins with a number of electron acceptors like o-chloranil, p-chloranil, 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) and vitamin K. The dependence of the CT transition energy on the donor ionization potential has been utilized to estimate the vertical electron affinities (E _A ^V) of [60]- and [70]fullerenes in solution. The value of E _A ^V for [60]fullerene is found to be 0.10 eV lower in magnitude than that of [70]fullerene. We have extracted degrees of CT, and oscillator and transition dipole strengths of the fullerenes/meso-tetraphenylporphyrins complexes. The experimental results show that the CT complexes studied here have a neutral character in their ground states. Electronic coupling elements have been determined for fullerene/meso-tetraphenylporphyrin complexes. Values of the solvent reorganization energy indicate that the electron transfer process takes place at a faster rate in the case of [70]fullerene/meso-tetraphenylporphyrin complexes.     

β-Tetra-brominated meso-tetraphenylporphyrin: A conformational study and application to the Mn-porphyrin catalyzed epoxidation of olefins with tetrabutylammonium oxone

X-ray crystallographic studies have shown that the free base β-tetra-brominated meso-tetraphenylporphyrin (H₂TPPBr₄) has a slightly ruffled structure with the dihedral angles of 70.1–79.2° between the phenyl groups and the porphyrin mean plane. The N(pyrrole)–N(pyrrolenine) distance is very similar to that of the standard planar porphyrins. The decreased N–H bond length of H₂TPPBr₄ with respect to that of meso-tetraphenylporphyrin (H₂TPP) seems to be due to the weaker intramolecular hydrogen bond of the former relative to the latter caused by the electron-withdrawing effects of the β-bromine substituents. The large red shifts of the Soret and Q(0,0) bands of H₂TPPBr₄ in comparison with those of H₂TPP, in spite of the nearly planar porphyrin core of the compound, also may be explained on the basis of the electron-withdrawing effects of the bromine atoms. Oxidation of styrene, the para-substituted derivatives and cyclooctene with tetrabutylammonium oxone in the presence of catalytic amounts of β-tetra-brominated meso-tetraphenylporphyrinatomanganese(III) acetate immediately gives the epoxide as the sole product. Terminal double bonds and unconjugated ones are less reactive than the conjugated double bonds and show lower selectivities. Catalytic activity of the electron-deficient Mn(H₂TPPBr₄)OAc dramatically depends on the Co-catalytic activity of the nitrogen donors as the axial base. The best axial bases are the nitrogenous donors with mixed σ- and π-donor ability to the metal centre.     

Coordination of nitrogen-containing ligands by Co complexes with tetra-and dodeca-substituted porphyrins

Capabilities of complexes with tetraphenylporphyrin, the derivative of tetrapyridiniumporphyrin, and with β-octabromine-meso-tetraphenylporphyrin to coordinate additional nitrogen-containing ligands are compared. The equilibrium constants of addition of extra ligands, namely, pyridine, piperidine, and N-methylimidazole, to the Co complexes with these porphyrins in ethanol solutions at 298 K are determined.     

Complex Formation and Spectral Properties of meso-Phenyltetrabenzoporphyrins in Pyridine and N,N-Dimethylformamide

Contributions of structural (macroring distortion) and polarization (in asymmetrically substituted derivatives) effects into the reactivity and chromophoric properties of substituted porphyrins were revealed on the basis of the kinetics of complex formation of nona-, deca-, undeca-, and dodecasubstituted porphyrins (meso-phenyltetrabenzoporphyrins) with Zn(OAc)₂ in pyridine and the electronic absorption spectra of the ligands and their complexes with Zn(II) and Cu(II) in pyridine and N,N-dimethylformamide (DMF). Dodecaphenyl substitution produces a weaker ring distortion in the more aromatic tetrabenzoporphyrin compared with porphyrins themselves. Irrespective of the degree of macroring nonplanarity, the Zn (II) and Cu complexes of tetrabenzoporphyrins with increasing degree of meso-phenyl substitution meet a spectral stability criterion.