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.

Long live the state! Photoexcitation of a zinc chlorin–fullerene dyad with a short linkage results in the formation of the ultra‐long‐lived charge‐separated (CS) state by a one‐step photoinduced electron transfer without loss of energy, which is inevitable for charge separation by multistep electron‐transfer processes. The lifetime of the charge‐separated state was 120 s in frozen PhCN at −150 °C (see picture).

Eleven free-base corroles with different electron-donating or electron-withdrawing meso substituents were characterized as to their electrochemistry and UV-visible spectroscopy in benzonitrile (PhCN) or pyridine containing tetra-n-butylammonium perchlorate (0.1 M). Six forms of the compounds with different numbers of protons and/or oxidation states were spectroscopically identified and are represented as (Cor)H3, (.Cor)H2, [(Cor)H2]-, [(.Cor)H2]2-, [(Cor)H4]+, and [(.Cor)H4]2+, where Cor is a trianionic corrole macrocycle. The electrochemistry and UV-visible properties are a function of corrole basicity, solvent basicity, and types or sizes of the meso substituents, and the compounds could be subdivided into one of two different groups, one of which comprises sterically hindered corroles and another that does not. The electroactive species in PhCN is (Cor)H3, whereas in pyridine, one inner proton dissociates, generating a mixture of (Cor)H3, [(Cor)H2]-, and pyH+. The addition of one electron to [(Cor)H2]- reversibly gives the [(.Cor)H2]2- pi-anion radical, whereas a reversible oxidation of the same species gives the neutral radical (.Cor)H2. The first one-electron reduction of (Cor)H3 occurs at the macrocycle in PhCN, but the initial product rapidly converts to [(Cor)H2]-, which undergoes additional reversible redox reactions at the conjugated pi-ring system. The first oxidation of (Cor)H3 in PhCN leads to a mixture of (.Cor)H2 and [(Cor)H4]+, both of which could be further oxidized or reduced. The UV-visible spectra of [(Cor)H4]+ were measured in PhCN after titrations with trifluoroacetic acid, after which selected samples were examined as to their electrochemistry. The HOMO-LUMO gaps of [(Cor)H2]-, (Cor)H3, and [(Cor)H4]+ were also determined.

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 beta-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 CH(2)Cl(2) 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 (Me(6)Et(2)Cor)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 CH(2)Cl(2) media, and ligand binding constants were evaluated using spectroscopic and electrochemical methods. The structure of (Me(4)Ph(5)Cor)Co(py)(2) was also determined by X-ray diffraction. Crystal data: (Me(4)Ph(5)Cor)Co(py)(2).3CH(2)Cl(2).H(2)O, orthorhombic, a = 19.5690(4) A, b = 17.1070(6) A, c = 15.9160(6) A, V = 5328.2(5) A(3), space group Pna2(1), Z = 2, 35 460 observations, R(F) = 0.069.

The synthesis and characterization of three new cofacial biscorroles and three new linked Co(II) porphyrins and Co(III) corroles with the same face to face orientation are described. The biscorroles are represented as (BCS)Co(2), (BCO)Co(2), (BCX)Co(2) while the porphyrin-corrole dyads are represented as (PCA)Co(2), (PCB)Co(2), (PCO)Co(2) where BC represents the Co(III) cofacial biscorroles and PC represents the porphyrin-corrole complexes which are linked to each other by a dibenzothiophene (S), dibenzofuran (O), or 9,9-dimethylxanthene (X) bridge in the case of the corroles and an anthracene (A), biphenylene (B), or dibenzofuran (O) bridge in the case of the mixed macrocycle derivatives. The electrochemical and spectroscopic data on these new bismacrocycles are compared to those of previously reported biscorroles of the type (BCA)Co(2) and (BCB)Co(2). The CO and/or pyridine binding properties of each biscorrole and porphyrin-corrole in CH(2)Cl(2) are also presented. Only one CO ligand is bound axially to each corrole unit of the bismacrocycle but five- and six-coordinate pyridine complexes can be generated for the same compounds, with the exact stoichiometry depending upon the concentration of pyridine in solution. In all cases, the six-coordinate bispyridine corrole complex can be unambiguously identified by a strong diagnostic marker band located at 598-601 nm. The formation constants for pyridine binding to the biscorroles range from log K(1) = 3.14 to 5.08 while log K(2) ranges from 1.10 to 2.61 depending upon the specific spacer. Carbon monoxide binding constants range from log K = 3.6 to 4.0 in the case of the biscorroles and from log K = 3.4 to 4.1 in the case of the porphyrin-corrole dyads. These values also depend on the specific spacer in the complex and, like the pyridine binding constants, decrease in the order BCO > BCA > BCB for the biscorroles and PCO > PCA > PCB for the porphyrin-corrole complexes.

The synthesis, spectroscopic properties, and electrochemistry of (BCA)Co(2) and (BCB)Co(2) are described where BCA and BCB represent biscorroles linked by an anthracenyl (A) or a biphenylenyl (B) bridge. The pyridine and CO binding properties of (BCA)Co(2) and (BCB)Co(2) are also presented, and one of the compounds in its pyridine-ligated form, (BCA)Co(2)(py)(3), is structurally characterized. The data on the biscorroles are compared on one hand to the monocorrole having the same substitution pattern and on the other hand to bisporphyrins having two Co(II) ions and the same anthracenyl or biphenylenyl linkers in order to better understand the interaction which occurs between the two corrole macrocycles. A parallel study on five different Co(III) phenyl-substituted corroles showed that bis-pyridine and mono-CO adducts are readily formed from the complexes in CH(2)Cl(2). This present paper examines how the ligand binding properties and electrochemistry of these Co(III) corroles are modified by the anthracenyl or biphenylenyl bridge which links the two macrocycles in a face to face orientation. An X-ray crystal structure was obtained for the tris-pyridine adduct of the anthracenyl bridged derivative, (BCA)Co(2)(py)(3), and gives the following results: C(127)H(99)Co(2)N(11).2CHCl(3), M = 2135.90, triclinic, space group P&onemacr;, a = 13.2555(5) A, b = 18.6406(8) A, c = 22.2140(9) A, alpha = 94.186(9) degrees, beta = 102.273(9) degrees, gamma = 94.205(9) degrees, V = 5326.8(4) A(3), 9293 independent reflections collected, R(F) = 0.066.

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.