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Four methylated N-confused free-base tetraarylporphyrins, which are represented as N-CH3(Ar)4NcpH2 (Ar =CH3OPh, CH3Ph, Ph or ClPh), were synthesized and characterized in terms of their spectral and electrochemical properties in nonaqueous media. The first one-electron oxidation of each porphyrin is reversible and located at E1/2=0.51–0.71 V, whereas the first one-electron reduction is quasi-reversible and located between −0.98 and −1.11 V vs. SCE. The electrochemically measured HOMO−LUMO gap ranged from 1.62 to 1.73 V, depending upon the solvent and meso-substituents on the macrocycle, and this range of values is similar to the HOMO−LUMO gaps of both the non-methylated N-confused porphyrins, (Ar)4NcpH2 (1.60–1.68 V), and the nitrated N-confused porphyrins, NO2(Ar)4NcpH2 (1.58–1.68 V). The effect of the N-methyl group on UV/Vis spectra and reduction/oxidation potentials as well as the mechanisms of electron transfer are discussed, and comparisons made with data in the literature for both the non-methylated N-confused porphyrins and related N-confused porphyrins having the same meso-substituents and an inner nitro-substituted carbon atom.

Four aryl-substituted tripyrrinone copper(II) complexes were synthesized and characterized as to their electrochemical and spectroelectrochemical properties. The examined compounds are represented as (YPh)3TPO2Cu, where TPO2 is a dianion of the tripyrrinone and Y is a CH3O, CH3, H or Cl substituent on the para-position of each phenyl ring of the compound. The neutral compounds are ESR active and show a typical d9 Cu(II) signal in frozen CH2Cl2 solution. Each Cu(II) compound undergoes three reductions between −0.61 and −1.90 V and two oxidations between 1.00 and 1.24 V in CH2Cl2 containing 0.1 mol/L tetra-n-butylammonium perchlorate. The potentials for oxidation are similar to those of copper tetraarylporphyrins but the reduction potentials are positively shifted as compared to the corresponding tetraarylporphyrins. Thus, the potential difference between the first one-electron oxidation and first one-electron reduction (the HOMO-LUMO gap) of (YPh)3TPO2Cu, which ranges from 1.68 to 1.75 V, is similar to that of copper corroles (1.73–1.85 V), but smaller than the separation of 2.30–2.37 V for the copper tetraarylporphyrins under the same solution conditions.

A series of N-confused free-base meso-substituted tetraarylporphyrins was investigated by electrochemistry and spectroelectrochemistry in nonaqueous media containing 0.1 M tetra-n-butylammonium perchlorate (TBAP) and added acid or base. The investigated compounds are represented as (XPh)4 NcpH2 , in which "Ncp" is the N-confused porphyrin macrocycle and X is a OCH3 , CH3 , H, or Cl substituent on the para position of each meso-phenyl ring of the macrocycle. Two distinct types of UV/Vis spectra are initially observed depending upon solvent, one corresponding to an inner-2H form and the other to an inner-3H form of the porphyrin. Both forms have an inverted pyrrole with a carbon inside the cavity and a nitrogen on the periphery of the π-system. Each porphyrin undergoes multiple irreversible reductions and oxidations. The first one-electron addition and first one-electron abstraction are located on the porphyrin π-ring system to give π-anion and π-cation radicals with a potential separation of 1.52 to 1.65 V between the two processes, but both electrogenerated products are unstable and undergo a rapid chemical reaction to give new electroactive species, which were characterized in the present study. The effect of the solvent and protonation/deprotonation reactions on the UV/Vis spectra, redox potentials and reduction/oxidation mechanisms is discussed with comparisons made to data and mechanisms for the structurally related free-base corroles and porphyrins.

Metalation of 6,13,20,21-tetraaryl-22H-[14]tribenzotriphyrins(2.1.1) (TriP, 1 a-d) with [Mn(CO)5 Br] provided Mn(I) tricarbonyl complexes of [14]tribenzotriphyrins(2.1.1) 2 a-d in 85-93 % yield. The complexes were characterized by mass spectrometry and UV/Vis absorption, IR, and NMR spectroscopy. Single-crystal X-ray analyses revealed that 2 b and 2 c adopt bowl-shaped conformations. The redox properties of [(TriP)Mn(I) (CO)3 ] (2 a-d) were studied by cyclic voltammetry. Each compound undergoes two reversible one-electron reductions to form a porphyrin π anion radical and a dianion in CH2 Cl2 . Two oxidation waves were observed, the first of which corresponds to a metal-centered electron-transfer process. The redox potentials of 2 a-d are consistent with the optical spectroscopic data and the relatively narrow HOMO-LUMO gaps that were predicted in DFT calculations. The optical spectra can be assigned by using Michl's perimeter model. TDDFT calculations predict the presence of several metal-to-ligand charge-transfer bands in the L-band region between 500 and 700 nm.

The first neo-confused hexaphyrin(1.1.1.1.1.0) was synthesized by oxidative ring closure of a hexapyrrane bearing two terminal "confused" pyrroles. The new compound displays a folded conformation with a short interpyrrolic C⋅⋅⋅N distance of 3.102 Å, and thus it readily underwent ring fusion to afford a neo-fused hexaphyrin with an unprecedented 5,5,5,7-tetracyclic ring structure. Furthermore, coordination of Cu(II) triggered a ring opening/contracting reaction to afford a Cu(II) complex of an N-linked pentaphyrin derivative. The roles of reactive N-C bonds in the porphyrinoid macrocycles were demonstrated.

A series of planar and nonplanar free-base b-pyrrole substituted meso-tetraarylporphyrins were characterized by electrochemistry, spectroelectrochemistry, and protonation or deprotonation reactions in neutral, acidic, and basic solutions of CH2Cl2. The neutral compounds are represented as H2(P), in which P represents a porphyrin dianion with one of several different sets of electron-withdrawing or -donating substituents at the messo and/or b-pyrrole positions of the macrocycle. The conversion of H2(P) to [H4(P)]2+ in CH2Cl2 was accomplished by titration of the neutral porphyrin with trifluoroacetic acid (TFA) while the progress of the protonation was monitored by UV/Vis spectroscopy, which was also used to calculate logb2 for proton addition to the core nitrogen atoms of the macrocycle. Cyclic voltammetry was performed after each addition of TFA or TBAOH to CH2Cl2 solutions of the porphyrin and half-wave potentials for reduction were evaluated as a function of the added acid or base concentration. Thin-layer spectroelectrochemistry was used to obtain UV/Vis spectra of the neutral and protonated or deprotonated porphyrins under the application of an applied reducing potential. The magnitude of the protonation constants, the positions of ?max in the UV/Vis spectra and the half-wave or peak potentials for reduction are then related to the electronic properties of the porphyrin and the data evaluated as a function of the planarity or nonplanarity of the porphyrin macrocycle. Surprisingly, the electroreduction of the diprotonated nonplanar porphyrins in acid media leads to H2(P), whereas the nonplanar H2(P) derivatives are reduced to [(P)]2- in CH2Cl2 containing 0.1m tetra-n-butylammonium perchlorate (TBAP). Thus, in both cases an electrochemically initiated deprotonation is observed. � 2014 Wiley-VCH Verlag GmbH& Co. KGaA, Weinheim.

Two iron(I) porphyrins were electrogenerated and then utilized as catalysts for the reductive dechlorination of 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT) in N,N′-dimethylformamide. No reaction is observed between DDT and the Fe(III) or Fe(II) forms of the porphyrin, but the electrogenerated Fe(I) porphyrin efficiently catalyzes the electroreduction of DDT to give (1,1-bis(4-chlorophenyl)-2,2-dichloroethane) DDD, (1,1-bis(4-chlorophenyl)-2,2-dichloroethylene) DDE and (1,1-bis(4-chlorophenyl)-2-dichloroethane) DDMU as determined by GC-MS analysis. The reductive dechlorination was monitored by electrochemistry, controlled potential electrolysis and spectroelectrochemistry and a mechanism for the reaction involving the reduced porphyrins and DDT is proposed. Comparisons are also made between the catalytic properties of metalloporphyrins containing iron, cobalt and manganese central metal ions under the same solution conditions.

A novel amphiphilic sandwich-type mixed (phthalocyaninato)(porphyrinato)europium double-decker complex Eu(Pc)-[T(OH) 3 PP] [Pc = phthalocyaninate, T(OH) 3 PP = 5,10,15-tris(4-hydroxyphenyl)-20-(4-tert-butylphenyl)porphyrinate] (1) was designed, prepared, and characterized by a range of spectroscopic methods in addition to elemental analysis. By employing a solution injection method, this compound self-assembles into nanoscale hollow spheres with an average diameter of ca. 70 nm. The hollow spherical structure was determined by transmission electronic microscopy and scanning electronic microscopy. Comparison in the electronic absorption spectrum between the aggregate and the compound itself in solution reveals the J-aggregation packing mode of the amphiphilic double-decker molecules in nanoscale hollow spheres. The present work represents the first example of nanoscale hollow sphere morphology self-assembled from sandwich tetrapyrrole rare-earth complexes.

The synthesis, catalytic properties, UV-visible spectra and electrochemistry of β-pyrrole brominated porphyrins are summarized in this brief review. The effect of the Br substituents of the porphyrin ring on the redox behavior, and on axial CO or pyridine binding to the porphyrins is also discussed.