Search

Neutral cobalt(II) phthalocyanine and 2,3- and 3,4-tetrapyridoporphyrazine complexes were examined in pyridine, dimethyl sulfoxide and N,N-dimethylformamide to evaluate their catalytic properties in the reductive dechlorination of 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (p,p'-DDT). Cyclic voltammetry, controlled potential bulk electrolysis and thin-layer UV-visible spectroelectrochemistry of each compound in the presence of DDT indicated that both the singly and doubly reduced species, [Co(I)]- and [Co(I)]2- , can catalyze the dechlorination of DDT through the formation of, and a photoinduced or electrochemically induced cleavage of, the Co-C bond in the organometallic intermediates. GC-MS analysis revealed that DDT was converted to 1,1-bis(4-chlorophenyl)-2, 2-dichloroethane (p,p'-DDD), 1,1-bis(4-chlorophenyl)-2,2-dichloroethylene (p,p'-DDE) and 1,1-bis(4-chlorophenyl)-2-chloroethylene (p,p'-DDMU), upon dechlorination. The catalytic performance of the three cobalt complexes depends upon the reactive nature of each compound, the solvent, the reaction time and the equivalence of DDT. In addition, either DDD or DDE can be catalytically dechlorinated to generate DDMU, possibly through a similar mechanism.

Two cobalt porphyrazines, 2,3-tetrapyridoporphyrazine and 3,4-tetrapyridoporphyrazine, were examined in N,N-dimethylformamide, dimethyl sulfoxide and pyridine solutions as to their electrochemical, spectroelectrochemical and ESR spectroscopic properties. These results were compared with those of the unsubstituted cobalt phthalocyanine. At high concentrations, aggregation was observed for each investigated compound in the three solvents. The intensity of ESR signals of each derivative depends upon the extent of aggregation in its solution. The g values shift towards high field with an increase in the strength of the axial ligand and the number of axial ligands on the cobalt center. Both tetrapyridoporphyrazine complexes undergo one oxidation and three reductions in N,N-dimethylformamide, dimethyl sulfoxide or pyridine solution. Thin-layer UV-visible spectroelectrochemical results confirmed that the first oxidation and first reduction of both compounds are metal-centered while the second and third reductions are ring-centered. An overall electron transfer mechanism for both porphyrazine derivatives is proposed.

A new synthesis is reported for hexadecafluorophthalocyanineruthenium(II), F16Pc (2-) RuIIand hexadecachlorophthalocyanineruthenium(II), Cl16Pc (2-) RuII, is reported for the first time. These paramagnetic species, which contain no axial ligand, are quite reasonably soluble in a range of common organic solvents. We report and discuss electronic and vibrational (infrared and resonance Raman) spectroscopic, MALDI-TOF and magnetic data. In addition we report electrochemical data and use spectroelectrochemical methods to obtain the electronic spectra of these species in the phthalocyanine(1-), (3-) and (4-) oxidation states.

Two α-substituted vanadium-oxo phthalocyanines, [( OC 6 H 3(t- Bu )2)4Pc] VO and [( OC 8 H 17)4Pc] VO , where OC 6 H 3(t- Bu )2 is 2,4-di-tert-butylphenoxy and OC 8 H 17 is 2,2,4-tri-methyl-3-pentoxy, were synthesized and characterized by elemental analysis, mass spectrometry, UV-visible, IR, ESR spectroscopy and electrochemistry. Both complexes have good solubility and do not aggregate in polar or non-polar solvents. Three reductions and two oxidations can be observed in DMF containing 0.2 M TBAP. A HOMO-LUMO gap of ~1.4 V is seen for both complexes. The first two one-electron reductions and first oxidation are reversible diffusion controlled electrode processes under the given experimental conditions. The effects of solvent and phthalocyanine macrocycle substituents on the Q bands of the electronic absorption spectra are discussed.

Three series of cobalt(III) corroles were tested as catalysts for the electroreduction of dioxygen to water. One was a simple monocorrole represented as (Me(4)Ph(5)Cor)Co, one a face-to-face biscorrole linked by an anthracene (A), biphenylene (B), 9,9-dimethylxanthene (X), dibenzofuran (O) or dibenzothiophene (S) bridge, (BCY)Co(2) (with Y = A, B, X, O or S), and one a face-to-face bismacrocyclic complex, (PCY)Co(2), containing a Co(II) porphyrin and a Co(III) corrole also linked by one of the above rigid spacers (Y = A, B, X, or O). Cyclic voltammetry and rotating ring-disk electrode voltammetry were both used to examine the catalytic activity of the cobalt complexes in acid media. The mixed valent Co(II)/Co(III) complexes, (PCY)Co(2), and the biscorrole complexes, (BCY)Co(2), which contain two Co(III) ions in their air-stable forms, all provide a direct four-electron pathway for the reduction of O(2) to H(2)O in aqueous acidic electrolyte when adsorbed on a graphite electrode, with the most efficient process being observed in the case of the complexes having an anthracene spacer. A relatively small amount of hydrogen peroxide was detected at the ring electrode in the vicinity of E(1/2) which was located at 0.47 V vs SCE for (PCA)Co(2) and 0.39 V vs SCE for (BCA)Co(2). The cobalt(III) monocorrole (Me(4)Ph(5)Cor)Co also catalyzes the electroreduction of dioxygen at E(1/2) = 0.38 V with the final products being an approximate 50% mixture of H(2)O(2) and H(2)O.

A bacteriochlorin-C60 dyad (H2BCh-C60) and a zinc chlorin dyad (ZnCh-C60) with the same short spacer have been synthesized. The rate constants for the charge-separation (CS) processes in these dyads were determined by fluorescence lifetime measurements of the dyads. The charge-recombination (CR) rate constants of the dyads were determined using laser flash photolysis. The photoexcitation of the zinc chlorin-C60 dyad results in formation of the long-lived radical ion pair, which has absorption maxima at 790 and 1000 nm due to the zinc chlorin radical cation and the C60 radical anion, respectively. Photoexcitation of the free-base bacteriochlorin-C60 dyad with the same short linkage leads to formation of the radical ion pair, which decays quickly to the triplet excited state of the bacteriochlorin moiety. The driving force dependence of the electron-transfer rate constants of these dyads with a short spacer affords a small reorganization energy (λ = 0.51 eV) as compared with the λ value (0.66 eV) of zinc po...

Two diruthenium(III,III) corrole dimers, [(Et 6 Me 2 Cor)Ru] 2 and [(Me 6 Et 2 Cor)Ru] 2 , where Et 6 Me 2 Cor and Me 6 Et 2 Cor are the 2,3,8,12,17,18-hexaethyl-7,13-dimethylcorrole and 8,12-diethyl-2,3,7,13,17,18-hexamethylcorrole trianions, respectively, were synthesized and characterized as to their spectroscopic and electrochemical properties. They exhibit up to three oxidations and two reductions by cyclic voltammetry in CH 2 Cl 2 or pyridine containing 0.1 M TBAP, almost all of which are electrochemically reversible on the voltammetric and/or thin-layer spectroelectrochemical timescale. The two reductions and the first two oxidations involve one-electron transfer processes which are separated from each other by 770–880 mV upon reduction and by 350–420 mV upon oxidation. The UV–vis spectroelectrochemical data suggest that the first two one-electron oxidations occur at the diruthenium metal centers while the third oxidation (seen only in CH 2 Cl 2 ) is proposed to be macrocycle-based, leading to the formation of a Ru 2 (IV,IV) corrole species. The formation of a Ru(III,IV) complex after abstraction of one electron is also suggested by the rhombic ESR spectrum of singly oxidized [(Me 6 Et 2 Cor)Ru] 2 at 77 K. The first one-electron reduction is also assigned as metal-centered and leads to the formation of a Ru 2 (III,II) complex. Finally, a comparison of electrochemical properties between the investigated diruthenium(III,III) corroles and an earlier characterized diruthenium(II,II) octaethylporphyrin, [(OEP)Ru] 2 , is presented.

The photochemical and electrochemical properties of four chlorin-C60 or porphyrin-C60 dyads having the same short spacer between the macrocycle and the fullerene are examined. In contrast with all the previous results on porphyrin-fullerene dyads, the photoexcitation of a zinc chlorin-C60 dyad results in an unusually long-lived radical ion pair which decays via first-order kinetics with a decay rate constant of 9.1 x 10(3) x s(-1). This value is 2-6 orders of magnitude smaller than values reported for all other porphyrin or chlorin donor-acceptor of the molecule dyad systems. The formation of radical cations of the donor part and the radical anion of the acceptor part was also confirmed by ESR measurements under photoirradiation at low temperature. The photoexcitation of other dyads (free-base chlorin-C60, zinc porphyrin-C60, and free-base porphyrin-C60 dyads) results in formation of the ion pairs which decay quickly to the triplet excited states of the chlorin or porphyrin moiety via the higher lying radical ion pair states as is expected from the redox potentials.

The synthesis, spectroscopic properties, and electrochemistry of six different alkyl- and aryl-substituted Co(III) corroles are presented. The investigated compounds contain methyl, ethyl, phenyl, or substituted phenyl groups at the eight β-positions of the corrole macrocycle and four derivatives also contain a phenyl group at the 10-meso position of the macrocycle. Each cobalt corrole undergoes four reversible oxidations in CH2Cl2 containing 0.1 M tetra-n-butylammonium perchlorate and exists as a dimer in its singly and doubly oxidized forms. The difference in potential between the first two oxidations is associated with the degree of interaction between the two corrole units of the dimer and ranges from an upper value of 0.62 V, in the case of (Me6Et2Cor)Co, to a lower value of about 0.17 V, in the case of four compounds which have a phenyl group located at the 10-meso position of the macrocycle. These Co(III) corroles strongly coordinate two pyridine molecules or one carbon monoxide molecule in CH2Cl2 ...

Dicobalt or heterobimetallic cofacial bisporphyrins are up till now amongst the very few molecular electrocatalysts able to promote the direct reduction of dioxygen to water via a four-electron process in acidic medium. Numerous studies have been devoted to elucidate the key steps of this catalytic reaction and an important result has revealed an unexpected high dioxygen affinity for a mixed valence Co(II)/Co(III) cofacial porphyrin, the key intermediate complex being a μ-superoxo derivative. At the same time, the great importance assumed by ‘Pacman’ porphyrins and the recent developments in corrole chemistry have provided the stimulation to synthesise porphyrin–corrole dyads which might also transport and/or activate dioxygen. In the present paper, we report the stepwise synthesis and characterisation of a cofacial porphyrin–corrole bearing an anthracenyl bridge, (PCA)H5 where PCA is the pentaanion of 1-(13,17-diethyl-2,3,7,8,12,18-hexamethylporphyrin–5-yl)-8-(7,8,12,13-tetramethyl-2,3,17,18-tetraphenylcorrol-10-yl) anthracene. The synthesis and characterisation of the μ-superoxo Co(III)/Co(III) complex 〚(PCA)Co2Im2〛(μ-O2) is also described.

The synthesis and electrochemical characterization of ‘crowned’ and ‘dioxocyclam’ metalloporphyrins containing Co(II) or Zn(II) metal ions is presented. Each complex is also characterized by mass spectrometry in addition to a variety of spectroscopic techniques (UV-vis, FTIR, ESR (in the case of Co(II)) and 1H and 13CNMR spectroscopy).

A series of manganese(III) corroles were investigated as to their electrochemistry and spectroelectrochemistry in nonaqueous solvents. Up to three oxidations and one reduction were obtained for each complex depending on the solvents. The main compound discussed in this paper is the meso-substituted manganese corrole, (Mes 2PhCor)Mn, and the main points are how changes in axially coordinated anion and solvent will affect the redox potentials and UV-vis spectra of each electrogenerated species in oxidation states of Mn(III), Mn(IV), or Mn(II). The anions OAc (-), Cl (-), CN (-), and SCN (-) were found to form five-coordinate complexes with the neutral Mn(III) corrole while two OH (-) or F (-) anions were shown to bind axially in a stepwise addition to give the five- and six-coordinate complexes in nonaqueous media. In each case, complexation with one or two anionic axial ligands led to an easier oxidation and a harder reduction as compared to the uncomplexed four-coordinate species.

Combined electrochemical and UV-visible spectroelectrochemical methods were utilized to elucidate the prevailing mechanisms for electroreduction of previously synthesized porphyrin-corrole dyads of the form (PCY)H2Co and (PCY)MClCoCl where M = Fe(III) or Mn(III), PC = porphyrin-corrole, and Y is a bridging group, either biphenylenyl (B), 9,9-dimethylxanthenyl (X), anthracenyl (A), or dibenzofuranyl (O). These studies were carried out in pyridine, conditions under which the cobalt(IV) corrole in (PCY)MClCoCl is immediately reduced to its Co(III) form, thus enabling direct comparisons with the free-base porphyrin dyad, (PCY)H2Co(III) under the same solution conditions. The compounds are all reduced in multiple one-electron-transfer steps, the first of which involves the M(III)/M(II) process of the porphyrin in the case of (PCY)MClCoCl and the Co(III)/Co(II) process of the corrole in the case of (PCY)H2Co. Each metal-centered redox reaction may be accompanied by the gain or loss of pyridine axial ligands, with the exact stoichiometry of the exchange process depending upon the specific combination of metal ions in the dyad, their oxidation states, and the particular spacer in the complex. Before this study was started, it was expected that the porphyrin-corrole dyads with the largest spacers, namely, O and A, would readily accommodate the formation of cobalt(III) bis-pyridine adducts because of the larger size of the cavity while dyads with the smallest B spacer would seem to have insufficient room to add even a single pyridine within the cavity, as was structurally seen in the case of (PCB)H2Co(py). This is clearly not the case, as shown in the present study. A reversible Co(III)/Co(II) reaction is seen for (PCB)MnClCoCl at -0.62 V, which when combined with spectroscopic data, leads to the assignment of (PCB)Mn(III)(py)2Co(III)(py) as the species in pyridine. The reduction of (PCB)Mn(III)(py)2Co(III)(py) to (PCB)Mn(II)(py)Co(III)(py) is accompanied on the slower spectroelectrochemical time scale by the appearance of a 603 nm band in the UV-vis spectra and is consistent with the addition of a second pyridine ligand to the Co(III)(py) unit of the dyad as one ligand is lost from the electrogenerated manganese(II) porphyrin, thus maintaining one pyridine ligand within the cavity. A different change in the coordination number is observed in the case of (PCB)FeClCoCl. Here the initial Fe(III) complex can be assigned as (PCB)Fe(III)ClCo(III)(py), which has no pyridine molecule within the cavity and the singly reduced form is characterized as (PCB)Fe(II)(py)2Co(III)(py)2, which contains two pyridine ligands inside the cavity. A following one-electron reduction of the Fe(II)/Co(III) complex then gives [(PCB)Fe(II)(py)2Co(II)]-.

Three face-to-face linked porphyrin-corrole dyads were investigated as to their electrochemistry, spectroelectrochemistry, and chloride-binding properties in dichloromethane or benzonitrile. The same three compounds were also investigated as to their ability to catalyze the electroreduction of dioxygen in aqueous 1 M HClO4 or HCl when adsorbed on a graphite electrode. The characterized compounds are represented as (PCY)H2Co, where P = a porphyrin dianion; C = a corrole trianion; and Y = a biphenylenyl, 9,9-dimethylxanthenyl, or anthracenyl spacer, which links the two macrocycles in a face-to-face arrangement. An axial binding of one or two Cl- ligands to the cobalt center of the corrole is observed for singly and doubly oxidized (PCY)H2Co, with the exact stoichiometry of the reaction depending upon the spacer size and the concentration of Cl- added to solution. No Cl- binding occurs for the neutral or reduced forms of the dyad, which contrasts with what is seen for the monocorrole, (Me4Ph5Cor)Co, where a single Cl- ligand is added to the Co(III) corrole in PhCN. The Co(III) form of the corrole in (PCY)H2Co also appears to be the catalytically active species in the electroreduction of dioxygen, which occurs at potentials associated with the Co(IV)/Co(III) reaction, that is, 0.35 V in 1 M HClO4 as compared to 0.31-0.42 V for the same three dyads in PhCN and 0.1 M TBAP. The potential for the catalytic electroreduction of O2 in HCl shifts negatively by 60 to 70 mV as compared to E(1/2) values in 1 M HClO4, consistent with the binding of Cl- to the Co(IV) form of the corrole and its rapid dissociation after electroreduction to Co(III) at the electrode surface.

The synthesis of a novel family of heterobinuclear cofacial biphenylene (B), anthracene (A), 9,9-dimethylxanthene (X), or dibenzofuran (O) bridged porphyrin-corrole complexes, (PCY)MClCoCl, is reported, M being either an iron(III) or manganese(III) ion. Each complex was characterized by electrochemistry, mass spectrometry, UV-vis, IR, and electron spin resonance spectroscopy. Unlike previously examined biscobalt porphyrin-corrole dyads, the cobalt ion of the corrole moiety is present in a high-valence +4 oxidation state, as proven by electrochemistry, spectroelectrochemistry, and an X-ray diffraction study of (PCB)FeClCoCl, which shows the presence of a bound Cl- anion on the cobalt corrole. Structural data: (PCB)FeClCoCl x 0.5(C7H16) x 0.5(CH2Cl2) x 2H2O, triclinic, space group P1, a = 13.8463(3) A, b = 16.8164(5) A, c = 17.9072(6) A, alpha = 93.780(1) degrees, beta = 111.143(1) degrees, gamma = 97.463(2) degrees, Z = 2.

The synthesis and characterization of cofacial copper biscorroles and porphyrin-corroles linked by a biphenylenyl or anthracenyl spacer are described. The investigated compounds are represented as (BCA)Cu(2) and (BCB)Cu(2) in the case of the biscorrole (BC) derivatives and (PCA)Cu(2) and (PCB)Cu(2) in the case of porphyrin (P)-corrole (C) dyads, where A and B represent the anthracenyl and biphenylenyl bridges, respectively. A related monomeric corrole (Me(4)Ph(5)Cor)Cu and monomeric porphyrin (Me(2)Et(6)PhP)Cu that comprise the two halves of the porphyrin-corrole dyads were also studied. Electron spin resonance (ESR), (1)H NMR, and magnetic measurements data demonstrate that the copper corrole macrocycle, when linked to another copper corrole or copper(II) porphyrin, can be considered to be a Cu(III) complex in equilibrium with a Cu(II) radical species, copper(III) corrole being the main oxidation state of the corrole species at all temperatures. The cofacial orientation of (BCB)Cu(2), (BCA)Cu(2), and (PCB)Cu(2) was confirmed by X-ray crystallography. Structural data: (BCB)Cu(2)(C(110)H(82)N(8)Cu(2).3CDCl(3)), triclinic, space group P, a = 10.2550(2) A, b = 16.3890(3) A, c = 29.7910(8) A, alpha = 74.792(1) degrees , beta = 81.681(1) degrees , gamma = 72.504(2) degrees , Z = 2; (BCA)Cu(2)(C(112)H(84)N(8)Cu(2).C(7)H(8).1.5H(2)O), monoclinic, space group P 2(1)/c, a = 16.0870(4) A, b = 35.109(2) A, c = 19.1390(8) A, beta = 95.183(3) degrees , Z = 4; (PCB)Cu(2)(C(89)H(71)N(8)Cu(2).CHCl(3)), monoclinic, space group P2(1)/n, a = 16.7071(3) A, b = 10.6719(2) A, c = 40.8555(8) A, beta = 100.870(1) degrees , Z = 4. The two cofacial biscorroles, (BCA)Cu(2) and (BCB)Cu(2), both show three electrooxidations under the same solution conditions. The reduction of (BCA)Cu(2) involves a reversible electron addition to each macrocycle at the same potential of E(1/2) = -0.20 V although (BCB)Cu(2) is reversibly reduced in two steps to give first [(BCB)Cu(2)](-) and then [(BCB)Cu(2)](2)(-), each of which was characterized by ESR spectroscopy as containing a Cu(II) center. These latter electrode reactions occur at E(1/2) = -0.36 and -0.51 V versus a saturated calomel reference electrode. The half-reduced and fully reduced (BCB)Cu(2) show similar Cu(II) ESR spectra, and no evidence of a triplet signal is observed. The two well-separated reductions of (BCB)Cu(2) to give [(BCB)Cu(2)](2)(-) can be attributed to a stronger pi-pi interaction between the two macrocycles of this dimer as compared to those of (BCA)Cu(2). The copper porphyrin-corrole dyads, (PCA)Cu(2) and (PCB)Cu(2), show five reversible oxidations and two reversible reductions, and these potentials are compared with corresponding values for electrochemical reactions of the porphyrin and corrole monomers under the same solution conditions.

Photoexcitation of an electron donor-acceptor linked dyad containing gold(III) and zinc(II) porphyrins (ZnPQ-AuIIIPQ+) results in electron transfer from the singlet excited state of ZnPQ to the metal center of AuPQ+ to produce the charge-separated state (ZnPQ*+-AuIIPQ) which has a long lifetime (10 mus) in nonpolar solvents such as cyclohexane and toluene.

Electrochemical and spectroelectrochemical studies are presented for nine copper corroles with electron-withdrawing or electron-donating substituents on the three meso-phenyl rings of the compounds or on the eight β-pyrrole positions of the macrocycle. Up to three reversible oxidations can be seen for each Cu (III) corrole in CH 2 Cl 2 containing 0.1 M TBAP. Unlike the case of ( OEC ) Cu , no dimer is electrochemically detected upon the first oxidation of these compounds at room temperature. However, a dimer forms at low temperature (< -50°C) for compounds having strong electron-donating groups. Two reductions are observed for all nine corroles at low temperature in CH 2 Cl 2, 0.1 M TBAP, but only one reduction is detected at room temperature for four of these compounds which have weak electron-withdrawing or electron-donating groups. The neutral, reduced or oxidized Cu corroles were also characterized by thin-layer UV-visible spectroelectrochemistry and ESR. The resulting data indicates that eight of the nine neutral complexes contain a Cu (III) center while only one complex, [ Br 8( C 6 F 5)3 Cor ] Cu , exists in its Cu (II) form in CH 2 Cl 2 containing 0.2 M TBAP.