Electrocatalytic Four-Electron Reduction of Dioxygen by 1,2-Phenylene-Bridged Dicobalt Diporphyrins

Park, Gil Jae; Nakajima, Satoshi; Osuka, Atsuhiro; Kim, Kimoon

doi:10.1246/cl.1995.255

Cited by 14 publications

(12 citation statements)

References 10 publications

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“…[35] The palladium complexes [Pd 2 (L)] can also be compared to Pacman diporphyrins that were synthesised by Naruta and co-workers, in which the two porphyrins are linked by a similar o-phenylene spacer. [36][37][38] In contrast to [Pd 2 (L)], meso-mesityl-substituted dicobalt complexes of these ligands adopt wedgedgeometries with large intermetallic separations (e.g., 6.570(2) ), [37] while dizinc analogues are truly cofacial and display short interplanar separations (3.43 ) due to favourable p-stacking interactions. [39] The intermetallic separation in the [Pd 2 (L)] complexes appears to be intrinsically linked to both the bite and twist angles, which are dependant on ligand substitution patterns.…”

Section: A C H T U N G T R E N N U N G (Dpx)] and [Pd 2 A C H T U N Gmentioning

confidence: 99%

Design and Synthesis of Binucleating Macrocyclic Clefts Derived from Schiff‐Base Calixpyrroles

Givaja

Volpe

Leeland

et al. 2007

Chemistry A European J

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The syntheses, characterisation and complexation reactions of a series of binucleating Schiff-base calixpyrrole macrocycles are described. The acid-templated [2+2] condensations between meso-disubstituted diformyldipyrromethanes and o-phenylenediamines generate the Schiff-base pyrrolic macrocycles H(4)L(1) to H(4)L(6) upon basic workup. The single-crystal X-ray structures of both H(4)L(3).2 EtOH and H(4)L(6).H2O confirm that [2+2] cyclisation has occurred, with either EtOH or H2O hydrogen-bonded within the macrocyclic cleft. A series of complexation reactions generate the dipalladium [Pd2(L)] (L=L(1) to L(5)), dinickel [Ni2(L(1))] and dicopper [Cu2(L)] (L=L(1) to L(3)) complexes. All of these complexes have been structurally characterised in the solid state and are found to adopt wedged structures that are enforced by the rigidity of the aryl backbone to give a cleft reminiscent of the structures of Pacman porphyrins. The binuclear nickel complexes [Ni2(mu-OMe)2Cl2(HOMe)2(H(4)L(1))] and [Ni2(mu-OH)2Cl2(HOMe)(H(4)L(5))] have also been prepared, although in these cases the solid-state structures show that the macrocyclic ligand remains protonated at the pyrrolic nitrogen atoms, and the Ni(II) cations are therefore co-ordinated by the imine nitrogen atoms only to give an open conformation for the complex. The dicopper complex [Cu2(L(3))] was crystallised in the presence of pyridine to form the adduct [Cu2(py)(L(3))], in which, in the solid state, the pyridine ligand is bound within the binuclear molecular cleft. Reaction between H(4)L(1) and [Mn(thf){N(SiMe(3))2}2] results in clean formation of the dimanganese complex [Mn2(L(1))], which, upon crystallisation, formed the mixed-valent complex [Mn2(mu-OH)(L(1))] in which the hydroxo ligand bridges the metal centres within the molecular cleft.

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Section: A C H T U N G T R E N N U N G (Dpx)] and [Pd 2 A C H T U N Gmentioning

confidence: 99%

Design and Synthesis of Binucleating Macrocyclic Clefts Derived from Schiff‐Base Calixpyrroles

Givaja

Volpe

Leeland

et al. 2007

Chemistry A European J

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“…1 In particular, faceto-face diporphyrins attached by a rigid spacer such as anthracene (DPA), biphenylene (DPB), or o-phenylene (Gable type) have given unique properties. [1][2][3][4][5][6][7][8][9][10] For instance, biscobalt porphyrin dimers having rigid spacers display four-electron reactivity from dioxygen to water. [3][4][5][6][7] Diporphyrins containing various metal ions such as Mn, 8 Ru, 9 or Os 10 also show extremely metal-specific reactivities toward small molecules in the binding pocket between two porphyrin units.…”

Section: Introductionmentioning

confidence: 99%

Synthesis, Properties, and Crystal Structure of a Novel Anthracene-Bridged Molybdenum−Zinc Porphyrin Dimer

et al. 2002

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The synthesis and properties of novel anthracene-bridged porphyrin dimers having an oxomolybdenum(V) porphyrin unit, H(2)(DPA)[Mo(V)O(OMe)] (1) and (DPA)[Mo(V)O(OMe)][Zn(II)(MeOH)] (2), and the relevant monomer porphyrin complexes Mo(V)O(MPP)OMe (3) and Zn(II)(MPP) (4) are presented. An oxomolybdenum(V) unit was introduced into one of the two porphyrins in DPA to give 1, which has a free-base porphyrin unit. By introducing a zinc(II) ion to the free-base part, a mixed-metal complex of 2 was prepared and isolated. The structure of 2 was analyzed by X-ray crystallography (2.(7)/(6)CH(2)Cl(2), triclinic, P(-)1 (no. 2), a = 15.2854(12) A, b = 19.9640(15) A, c = 13.6915(12) A, alpha = 90.968(3), beta = 113.108(4), gamma = 96.501(4), Z = 2, R1 = 9.9, wR2 = 19.2). The structure of 2 demonstrated that a methanol is stably coordinated to the Zn(II) ion with the aid of a hydrogen bond to the methoxo ligand on the Mo(V) ion in the binding pocket of DPA. The electrochemical measurements of 2 suggested that the methanol was kept in the pocket of DPA in solution even at the reduced state of the molybdenum ion.

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“…Dicobalt cofacial diporphyrins − are among the very few molecular electrocatalysts 6-8 able to promote the direct reduction of dioxygen to water by a four-electron mechanism in an acidic medium. Mononuclear derivatives under the same conditions reduce dioxygen to hydrogen peroxide by a two-electron process .…”

mentioning

confidence: 99%

“…Understanding the catalytic cycle by which this four-electron reduction of O 2 proceeds and the properties critical for the catalyst's efficiency is a challenge of relevance to electrocatalysis for catalyst design and improvement as well as to bioinorganic reduction of O 2 by dinuclear systems such as cytochrome c oxidase, non-heme diiron sites, copper oxidases, etc. However, the exact mechanism for this catalysis has yet remained elusive in spite of the amount of related research. − ,, Actually, the four-electron reduction process is only observed when the dicobalt dimers are adsorbed on an edge plane graphite electrode (EPGE) immersed in aqueous acid. Under these conditions, the redox exchanges, their sites on the molecule, the complexation of O 2 , and protonation steps are practically impossible to determine.…”

mentioning

confidence: 99%

Reactivity toward Dioxygen of Dicobalt Face-to-Face Diporphyrins in Aprotic Media. Experimental and Theoretical Aspects. Possible Mechanistic Implication in the Reduction of Dioxygen

et al. 1997

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The reactivity toward dioxygen of two series of dicobalt cofacial diporphyrins in solution in an aprotic solvent is described. Some of these compounds are efficient electrocatalysts for the four-electron reduction of dioxygen when adsorbed on a graphite electrode immersed in aqueous acid. Their electrochemical and spectroscopic (UV−vis, EPR) behavior in solution shows that, contrary to what is observed with cobalt monomers, the neutral [PCoII CoIIP] (1) (P stands for a porphyrin ring) form does not react with dioxygen. Uniquely the one- and two-electron-oxidized forms of the dimer, [PCoII·CoIIP]+ (1 + ) and [PCoII---CoIIP]2+ (1 2+ ), respectively, reversibly bind dioxygen, giving two complexes, 2 and 3, at room temperature and in the absence of a good axial ligand. The stability constants of the two O2 complexes have been measured spectrophotometrically and/or electrochemically, and prove to be remarkably high. As a whole, the present O2 binding processes appear unprecedented as basically different in many respects from the process classically described in the case of cobalt monomers. Extended Hückel molecular orbital (EHMO) calculations, based on the crystal structure of the Co2FTF4 dimer in its uncomplexed form (Co−Co distance 3.42 Å), show that, in the absence of very important deformations of its structure, the only possible geometry for the O2 complex of the two-electron-oxidized derivative [PCo−O2−CoP]2+ (3) is the μ-η2:η2-peroxo structure. The calculated corresponding electronic diagram affords a rationale for most of the experimentally observed properties. Specifically, the O2 complex of the one-electron-oxidized form [PCo−O2 •−CoP]+ (2), the reduced form of complex 3, should be considered as a species in which the O2 moiety is further reduced, at least partially, as compared to its peroxo state in 3, i.e., consequently in an oxidation state intermediate between peroxo (−1) and oxo (−2). Preliminary results indicate that this species reacts with one proton, while the two-electron-oxidized O2 complex 3 is resistant to protonation. The possible implications of these specific properties of the dicobalt dimers in the four-electron reduction mechanism of O2 are discussed, and structural and mechanistic similarities with bioinorganic dinuclear sites appear significant.

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Electrocatalytic Four-Electron Reduction of Dioxygen by 1,2-Phenylene-Bridged Dicobalt Diporphyrins

Abstract: 1,2-Phenylene-bridged dicobalt diporphyrin 1 catalyzes efficiently the four-electron reduction of dioxygen to water in acidic solution. The catalytic activity of the diporphyrin is strongly affected by the substituents on the phenyl rings attached to the porphyrin macrocycles.

Cited by 14 publications

References 10 publications

Design and Synthesis of Binucleating Macrocyclic Clefts Derived from Schiff‐Base Calixpyrroles

Design and Synthesis of Binucleating Macrocyclic Clefts Derived from Schiff‐Base Calixpyrroles

Synthesis, Properties, and Crystal Structure of a Novel Anthracene-Bridged Molybdenum−Zinc Porphyrin Dimer

Reactivity toward Dioxygen of Dicobalt Face-to-Face Diporphyrins in Aprotic Media. Experimental and Theoretical Aspects. Possible Mechanistic Implication in the Reduction of Dioxygen

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