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Zinc tetraphenylporphyrin (TPP)Zn was examined as to its as to its electroreduction properties by cyclic voltammetry and spectroelectrochemistry in six nonaqueous solvents containing tetrabutylammonium perchlorate (TBAP). The porphyrin undergoes an initial one-electron reduction to give a [Formula: see text]-anion radical on the cyclic voltammetry timescale but the radical was not stable on the spectroelectrochemical timescale when utilizting chlorinated alkane solvents containing 0.1 M TBAP (CH2Cl2, 1-2,dichloroethane (C2H4Cl[Formula: see text] where chloride, generated from minute amounts of reduced solvent, formed an axially coordinated complex, (TPP)Zn[Formula: see text](Cl[Formula: see text], prior to reduction of the porphyrin. This spectroelectrochemically characterized product exhibits red-shifted Soret and Q-bands as compared to that of the neutral (TPP)Zn under the same solution conditions and analytical plots obtained from recording the spectrum as a function of potential rule out the possibility of forming the superoxide complex, (TPP)Zn[Formula: see text](O[Formula: see text], in chlorinated alkane solvents.

The electronic structures and, particularly, the nature of the HOMO in a series of PcFeL2, PcFeL'L″, and [PcFeX2]2- complexes (Pc = phthalocyaninato(2-) ligand; L = NH3, n-BuNH2, imidazole (Im), pyridine (Py), PMe3, PBu3, t-BuNC, P(OBu)3, and DMSO; L' = CO; L″ = NH3 or n-BuNH2; X = NCO-, NCS-, CN-, imidazolate (Im-), or 1,2,4-triazolate(Tz-)) were probed by electrochemical, spectroelectrochemical, and chemical oxidation as well as theoretical (density functional theory, DFT) studies. In general, energies of the metal-centered occupied orbitals in various six-coordinate iron phthalocyanine complexes correlate well with Lever Electrochemical Parameter EL and intercross the phthalocyanine-centered a1u orbital in several compounds with moderate-to-strong π-accepting axial ligands. In these cases, an oxidation of the phthalocyanine macrocycle (Pc(2-)/Pc(1-)) rather than the central metal ion (Fe(II)/Fe(III)) was theoretically predicted and experimentally confirmed.

The coordination chemistry of corrole has witnessed a great improvement in the past few years and its Periodic Table has been widened to be so large that it is compared with that of porphyrins. However, Ni and Zn ions, commonly used with porphyrins for both synthetic and theoretical purposes, are sparsely reported in the case of corroles. Here, we report synthetic protocols for preparing Ni and Zn triarylcorrole complexes. In the case of Zn, the preliminary oxidation of the free base corrole in DMSO to the neutral corrole radical is a necessary step to obtain the coordination of the metal ion, because the direct reaction led to the formation of an open-chain tetrapyrrole. The Ni complex could be directly obtained by heating the free base corrole and Ni(II) salt to 100 °C in a DMSO solution containing FeCl3. The non-innocent nature of the corrole ligand for both complexes has been elucidated by EPR, and in the case of the Zn derivative the first spectroelectrochemical characterization is presented. peerReviewed

Six [Formula: see text],[Formula: see text]-butano substituted metalloporphyrins containing sterically hindered meso-dihalogenophenyl substituents and first-row transition metal ions were synthesized and their electrochemical and spectroelectrochemical properties were characterized in nonaqueous media. The investigated compounds have the general formula butano(Y2Ph)4PorM, where Por is a dianion of the porphyrin, M = Mn[Formula: see text]Cl, Fe[Formula: see text]Cl, Co[Formula: see text], Ni[Formula: see text], Cu[Formula: see text] or Zn[Formula: see text]and Y2Ph is a sterically hindered 2,6-F2Ph or 2,6-Cl2Ph group on each of the four meso-positions of the macrocycle. The electrochemistry of each porphyrin was examined in CH2Cl2or pyridine containing 0.1 M tetra-[Formula: see text]-butylammonium perchlorate. The first one-electron reduction is metal-centered for the manganese(III), iron(III) and cobalt(II) porphyrins to generate the Mn(II), Fe(II) and Co(I) porphyrins, but it is porphyrin ring-centered for the other examined M(II) porphyrins to give porphyrin [Formula: see text]-anion radicals under the given solution conditions. The effect of the [Formula: see text],[Formula: see text]-butano and sterically hindered meso-Y2Ph substituents on redox potentials and electron transfer mechanisms are discussed and compared to what was previously reported for butano-substituted tetraarylporphyrins without hindered meso-substituents.

A series of nickel(II) monobenzochlorins (MBCs) and monobenzoporphyrins (MBPs) containing β-appended or meso,β-fused indanedione (IND) or malononitrile (MN) groups were synthesized and characterized for their physicochemical, electrochemical and anion sensing properties. Each investigated compound contained four meso-phenyl rings and a single β,β′-fused 4,5-di(methoxycarbonyl)benzene ring, with the chlorins represented as NiMBC(Y)2(R)4 and the porphyrins as NiMBP(YF)2, where Y is an indanedione (IND) or malononitrile (MN) group, R = H or Br and YF is a meso,β-fused IND or MN substituent. One of the investigated compounds, NiMBP(IND)2, was structurally characterized and shown to possess a ruffled macrocyclic conformation. The monobenzochlorins, NiMBC(IND)2, NiMBC(IND)2Br4 and NiMBC(MN)2, reversibly respond to basic anions such as CN−, F−, OAc− and H2PO4− through a visible color change assigned to the deprotonation of the vicinal proton on the appended IND or MN substituents. The malononitrile-fused NiII monobenzoporphyrin, NiMBP(MN)2, exhibited a selective but irreversible visual detection of cyanide ions (LOD = 2.23 ppm). This reaction afforded a tri-fused π-extended monobenzoporphyrin product represented as NiMBP(VCN)2 (where VCN = meso,β-fused vinyl cyanide) in non-aqueous media and proceeded via anion induced electron transfer (AIET). The in situ generated π-extended porphyrin was also isolated and characterized as to its physicochemical and electrochemical properties and found to possess a narrow electrochemical HOMO–LUMO gap of 1.46 V along with a near-IR (NIR) absorption band located at 861 nm.

The interacting effect of fused indanedione (IND) groups and antipodal Br [Formula: see text]-substituents on the electroreduction of free-base and transition metal tetraphenylporphyrins (TPPs) are elucidated through the use of cyclic voltammetry. A systematic study of the reduction potentials for mono- and di-fused derivatives of MTPP(IND)(R)2 and MTPP(IND)2(R)2 where R = Br or H and M = Cu[Formula: see text], Ni[Formula: see text], Zn[Formula: see text] or H2 is carried out in pyridine containing 0.1 M tetrabutylammonium perchlorate (TBAP) as supporting electrolyte and demonstrates how the overall electrochemical properties of these compounds can be tuned by systematic changes in the number of meso-[Formula: see text]fused IND groups on the molecule and the presence or absence of electron-withdrawing Br [Formula: see text]-substituents. Under these solution conditions, two reversible one-electron reductions are seen for H2TPP, while three reversible reductions are obtained for H2TPP(IND) or H2TPP(IND)Br2 and four for H2TPP(IND)2Br2. Multiple reductions also occur for the other investigated mono- and di-fused metalloporphyrins. Plots of measured [Formula: see text] values for the two ring-centered reductions of compounds in a given series vs. the number of fused IND groups are linear and with slopes varying in magnitude between 15 and 230 mV/IND depending upon the product of the electron transfer (anion radical or dianion), the specific central metal ion and the presence or absence of Br substituents on the pyrrole ring opposite the fused IND group(s). It is anticipated that the information from this study can be used for predicting the reduction potentials for yet to be synthesized compounds where a specific redox reactivity is desired.

Meso-tetrapyrenylporphyrin and its metal (Co[Formula: see text], Cu[Formula: see text], Ni[Formula: see text] and Zn[Formula: see text]) complexes were synthesized, characterized and studied for their spectral, electrochemical and energy transfer properties. DFT optimization was carried out to gain an insight into the interactions between the porphyrin [Formula: see text]-system and the pyrenyl substituents. The pyrenyl substituents and the porphyrin core remain essentially orthogonal to each other in both the free base and the metallated porphyrins. Redox potentials of the pyrenylporphyrins are marginally shifted as compared to their corresponding phenyl derivatives. Förster resonance energy transfer (FRET) studies were carried out in toluene for free-base pyrenylporphyrin and its Zn(II) complex. Since pyrene is a good donor, an efficient energy transfer from pyrene (D) to the porphyrin core (A) on the order of 80–85% was observed for these two compounds. It was observed that energy transfer occurs mainly via ”through-bond” (TB) interaction rather than ”through-space” (TS) interaction.

New Fe[Formula: see text] complexes of formula [Py8TPyzPzFe] · xH2O, its bis-pyridine adduct [Py8TPyzPzFe(py)2] · xH2O, the pentanuclear species [(MCl[Formula: see text]Py8TPyzPzFe] · xH2O (M [Formula: see text] Pd[Formula: see text], Pt[Formula: see text] and the bis-DABCO adducts [Py8TPyzPzFe(DABCO)2] · 11H2O and [(PdCl[Formula: see text]Py8TPyzPzFe(DABCO)2] · H2O (Py8TPyzPz [Formula: see text] octapyridino-tetrapyrazinoporphyrazinato dianion; DABCO [Formula: see text] 1,4-diazabiciclo[2.2.2]octane) were synthesized and characterized by elemental and thermogravimetric analysis, IR and UV-vis spectroscopy, with added studies on the starting complex [Py8TPyzPzFe] · xH2O regarding magnetic and electrochemical behavior. Clathrated water molecules are present in all compounds and have little to no effect on their physicochemical behavior as was observed for all previously reported analogs. UV-vis spectra of the mononuclear [Py8PyzPzFe] · xH2O complex in DMSO and pyridine are indicative of aggregation immediately after dissolving the compound. However, the spectra change slowly over time leading to formation of a porphyrazine species having spectral features typical of a monomer. UV-vis spectra of the parent pentanuclear [(MCl[Formula: see text]Py8TPyzPzFe] · xH2O (M [Formula: see text] Pd[Formula: see text], Pt[Formula: see text] complexes show a smaller degree of aggregation upon dissolution in DMSO or pyridine and the spectra of these solutions also change over time to those of a monomer. The presence of aggregation, spectral evolution with time and final species formed from the N-base adducts [Py8TPyzPzFe(DABCO)2] · 11H2O and [(PdCl[Formula: see text]Py8TPyzPzFe(DABCO)2] · H2O are reported and discussed.

Three copper dibenzoporphyrin(2.1.2.1) complexes having two dipyrromethene units connected through

The electronic structures and, particularly, the nature of the HOMO in a series of PcFeL

The autocyclotetramerization of the precursor 2,3-dicyano-5,6-di(2'-pyridyl)pyrazine [(CN)2Py2Pyz] in the presence of MCl3 compounds (M = AlIII, GaIII) leads to the formation of the new mononuclear porphyrazine complexes [Py8TPyzPzMCl]·xH2O (Py8TPyzPz = tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazinato anion). From these species, the hydroxide analogues [Py8TPyzPzMOH]·xH2O were obtained by contact with hot water, and their corresponding pentanuclear species [(PdCl2)4Py8TPyzPzMCl]·xH2O could be easily formed by the reaction with PdCl2. Physicochemical characterization of the mono- and pentanuclear macrocycles was based on elemental analysis, and mass, powder X-ray, and IR spectra. UV-vis spectral studies of the mononuclear species in solutions of DMF, DMSO, or pyridine (c ≈ 10-5-10-6 M) indicate (mainly in DMF and DMSO) the initial presence of aggregation, in some cases accompanied by the concomitant occurrence for the complex of a one-electron reduction. While disaggregation into a single species evolves spontaneously over time, the -1 charged species, eventually also found present, can be brought back to its neutral form by addition of a slight amount of HCl, the final spectrum showing the presence of the starting neutral species in its pure monomeric form. Similar aspects were faced also for the parent pentanuclear complexes. Cyclic voltammetry experiments, conducted for the mono-/pentanuclear complexes in DMF and DMSO (c ≈ 10-4 M), exhibit progressive one-electron reductions (1 → 4) characterized by E1/2 values (V vs SCE) positioned to significantly less negative values than those known for the phthalocyanine (Pc) analogues, these data confirming the previously already proven higher electron-deficient character of the MII derivatives of the Py8TPyzPz macrocycle with respect to Pc. The role of the present new series of AlIII and GaIII macrocyclic species to act as photosensitizers for the generation of singlet oxygen, 1O2, the cytotoxic agent in the anticancer treatment known as photodynamic therapy (PDT), has been explored in DMF/HCl. Among the quantum yields ΦΔ, the value found for the GaIII complex [Py8TPyzPzGaCl] (0.68), practically coincident with that observed for the TTDPz analogue (0.69), is well above those of most porphyrazines analogues (ΦΔ = 0.4-0.6), a result encouraging further research work for potential applications in the biochemical field.

Two octahalogenated nickel(II) hydroxyphenylporphyrins were synthesized and characterized as to their electrochemical and spectroscopic properties as well as their reactivity in neutral, acidic, and basic nonaqueous media. The newly synthesized complexes are represented as NiPorCl

Four tetrabutano and tetrabenzoporphyrins containing sterically hindered meso-(2,6-difluorophenyl) substituents and copper(II) or manganese(III) central metal ions were synthesized and characterized as to their electrochemical and spectroelectrochemical properties in nonaqueous media. The copper(II) derivatives exhibit the expected two one-electron reductions to give [Formula: see text]-anion radicals and dianions in CH2Cl2. Electrochemical and spectroelectrochemical data suggest that a Cu(II) phlorin anion is generated from the doubly reduced Cu(II) butanoporphyrin and it is this species which undergoes the third reduction in pyridine. The first one-electron reduction of the Mn(III) porphyrins is metal-centered to give a Mn(II) compound, while the second and third reductions are macrocycle-centered to give Mn(II) porphyrin [Formula: see text]-anion radicals and dianions in both CH2Cl2 and pyridine. A Mn(II) phlorin anion is also generated from the Mn(II) dianion on the spectroelectrochemical timescale under the given solution conditions. The [Formula: see text],[Formula: see text]-butano and benzo groups have a significant effect on the measured redox potentials. Steric hindrance of the meso-(2,6-difluorophenyl) substituents also has an effect on the potential separation between the first two oxidations of the benzoporphyrins.

The role of metal ions in promoting electron transfer processes in biological coenzymes is of great significance not only to understand their mechanistic details but also due to their direct utiliz...

The electroreductive dechlorination of γ-hexachlorocyclohexane (lindane) was investigated in non-aqueous media using as a catalyst the dirhodium complex Rh2(dpf)4, where dpf = the anion of N, N′-diphenylformamidinate. Rh2(dpf)4 undergoes two reversible one-electron redox processes in pyridine and/or N,N′-dimethylformamide (DMF), corresponding respectively to Rh24+/Rh25+ and Rh24+/Rh23+. Electrochemical and spectroelectrochemical measurements indicate that lindane reacts with the Rh23+ center in singly reduced [Rh2(dpf)4]−, giving a transient carbon-bonded dirhodium complex along with Cl−. Further catalytic dechlorination of lindane subsequently occurs with the activity of Rh2(dpf)4 as a catalyst depending upon the solvent conditions. Rh2(dpf)4 shows a higher catalytic reduction current in pyridine than in DMF for the degradation of lindane. This catalytic current can be further enhanced if 6% water (v/v) is added to the pyridine solution. Bulk controlled-potential electrolysis combined with GC–MS verified that although the addition of water to the neat pyridine increased the catalytic activity of Rh2(dpf)4, neat pyridine is still a better solvent for the formation of more extensively dechlorinated products of lindane. In neat pyridine, lindane can be converted stepwise to tetrachlorocyclohexene, dichlorobenzene isomers, chlorobenzene and the fully dechlorinated product benzene, the last of which becomes predominant at the end of the electrolysis. In pyridine having 6% added water, other than those dechlorinated products seen above, trichlorobenzene isomers are formed upon lindane degradation. Meanwhile, the relative concentrations of dichlorobenzene isomers and chlorobenzene become higher, while the yield of benzene becomes lower than the corresponding results obtained in neat pyridine. Based on the measured distribution of the products under the different solvent conditions, an overall pathway for the degradation of lindane is proposed.

Three cobalt dipyrrin-bisphenol (DPPCo) complexes with different meso-aryl groups (pentafluorophenyl, phenyl, and mesityl) were synthesized and characterized based on their electrochemistry and spectroscopic properties in nonaqueous media. Each DPPCo undergoes multiple oxidations and reductions with the potentials, reversibility, and number of processes depending on the specific solution conditions, the specific macrocyclic substituents, and the type and number of axially coordinated ligands on the central cobalt ion. Theoretical calculations of the compounds with different coordination numbers are given in the current study in order to elucidate the cobalt-ion oxidation state and the innocence or noninnocence of the macrocyclic ligand as a function of the changes in the solvent properties and degree of axial coordination. Electron paramagnetic resonance spectra of the compounds are obtained to experimentally assess the electron spin state. An X-ray structure of the six-coordinate complex is also presented. The investigated chemical properties of DPPCo compounds under different solution conditions are compared to those of cobalt corroles, where the macrocycle and metal ion also possess formal 3- and 3+ oxidation states in their air-stable forms.

The axial coordination properties of six zinc tetraarylporphyrins with seven different nitrogenous bases were examined in CH2Cl2 for derivatives containing four [Formula: see text],[Formula: see text]-fused butano or benzo groups and the equilibrium constants (log[Formula: see text] determined using spectral titration methods. The examined compounds are represented as butano(YPh)4PorZn and benzo(YPh)4PorZn, where Por is the porphyrin dianion and Y is a CH3, H or Cl substituent on the para-position of each meso-phenyl ring of the macrocycle. The initial four-coordinate butano- and benzoporphyrins will axially bind one nitrogenous base to form five-coordinate derivatives in CH2Cl2 and this leads to a 4–22 nm red-shift of the Soret and Q bands. The log[Formula: see text] values range from 1.98 to 4.69 for butano(YPh)4PorZn and from 3.42 to 5.36 for benzo(YPh)4PorZn, with the exact value depending upon the meso and [Formula: see text]-substituents of the porphyrin and the conjugate acid dissociation constants (p[Formula: see text] of the nitrogenous base.

Silver corrolates are attractive compounds from both practical and theoretical points of view. Indeed, they play a key role in peripheral functionalization reactions occurring at the macrocycle, enabling high-yield and regioselective group insertions useful to further elaborate the molecular skeleton. In parallel, the Janus innocent or noninnocent behavior of the corrole ligand in these complexes makes their description particularly challenging. Herein, we report properties for a series of silver 3,17-disubstituted triarylcorrole complexes with various functionalities (halogens or different phenylethynyl units) that deeply affect the electron density in the macrocyclic ligand, with obvious repercussions on the observed spectral characteristics. The compounds were obtained in yields of 54-92% by applying the Stille coupling reaction with the appropriate tributylethynyl stannane. Among the complexes prepared was a derivative bearing two terminal acetylenic units which opens the way to "click" reactions for new corrole-based architectures. This corrole was structurally characterized by single crystal X-ray crystallography. The addition of substituted ethynyl groups resulted in red-shifts of the electronic absorption spectra, the largest of which was observed for the compound with two β-NO2-Ph-C[triple bond, length as m-dash]C substituents. The remarkable influence of the NO2 groups on the electron density of this macrocycle was further demonstrated by electrochemical measurements, where an easier reduction of this complex derivative was observed as compared to the others. DFT calculations showed full delocalization over the entire p-nitrophenylethynyl unit of 5, largely affecting orbital distributions and the corresponding electronic absorptions. Although a variation of the β-substituents dramatically modifies the Soret- and Q-band positions towards lower energies for all the examined complexes, the saddling of the macrocycle resulting from functionalization is only moderate. The collected results suggest the description of these compounds as AgIII-corrolate3-, a metallocorrole with an innocent macrocyclic ligand.

Five meso-tetraaryl open-chain pentapyrroles were synthesized and characterized as to their electrochemistry and protonation reactions in nonaqueous media. The investigated compounds are represented as (Ar)4PPyH3 where Ar [Formula: see text],[Formula: see text]-F2Ph, [Formula: see text]-BrPh, Ph, [Formula: see text],[Formula: see text],[Formula: see text]-(OMe)3Ph or [Formula: see text]-MePh and were characterized by UV-vis and 1H NMR spectroscopy, mass spectrometry and electrochemistry. Cyclic voltammetry was used to measure redox potentials, while protonation involving the conversion of (Ar)4PPyH3 to [(Ar)4PPyH5][Formula: see text] was monitored by UV-vis absorption spectroscopy. Equilibrium constants for proton addition were calculated using the Hill equation. One of the pentapyrroles was also structurally characterized. The electrochemical data, protonation constants and crystal structure were then compared with data for previously examined pentapyrroles and analyzed as a function of the solvent properties and nature of substituents on the meso-phenyl rings of the macrocycle.