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Research paper thumbnail of Synthesis, characterization and X-ray crystal structures of cyclam derivatives. 7. Hydrogen-bond induced allosteric effects and protonation cooperativity in a macrotricyclic bisdioxocyclam receptor

New Journal of Chemistry, 2005

Research paper thumbnail of Cobalt(III) Corroles as Electrocatalysts for O2 Reduction: Reactivity of a Monocorrole, Biscorroles, and Porphyrin–Corrole Dyads

Le travail de recherche concerne l'électroreduction catalytique du dioxygène par des complexe... more Le travail de recherche concerne l'électroreduction catalytique du dioxygène par des complexes de cobalt adsorbés à la surface d'électrodes de graphite. Les systèmes bismacrocycliques étudiés se composent soit d'un corrole de cobalt(III) lié à une porphyrine de cobalt(II) soit de deux corroles de cobalt(III) maintenus face-à-face par un espaceur aromatique. En employant des espaceurs rigides tels que l'anthracène (A), le biphenylène (B), le 9,9-dimethylxanthène (X) ou le dibenzofurane (O), il est possible de varier la distance cobalt-cobalt entre les deux unités macrocycliques. L'étude des propriétés catalytiques de ces complexes à l'aide d'une électrode tournante disque-anneau indique que les porphyrin-corroles (PCY)Co2 et les biscorroles (BCY)Co2 (avec Y = A, B, X ou O) catalysent la réduction du dioxygène en eau selon un processus à 4 électrons et 4 protons avec une sélectivité plus élevée par rapport au processus de réduction à 2 électrons conduisant ...

Research paper thumbnail of Cobalt(III) Corroles as Electrocatalysts for the Reduction of Dioxygen:  Reactivity of a Monocorrole, Biscorroles, and Porphyrin−Corrole Dyads

Journal of the American Chemical Society, 2005

Three series of cobalt(III) corroles were tested as catalysts for the electroreduction of dioxyge... more Three series of cobalt(III) corroles were tested as catalysts for the electroreduction of dioxygen to water. One was a simple monocorrole represented as (Me4Ph5Cor)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)Co2, 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)Co2, and the biscorrole complexes, (BCY)Co2, which contain two Co(III) ions in their air-stable forms, all provide a direct four-electron pathway for the reduction of O2 to H2O 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 E1/2 which was located at 0.47 V vs SCE for (PCA)Co2 and 0.39 V vs SCE for (BCA)Co2. The cobalt(III) monocorrole (Me4Ph5Cor)Co also catalyzes the electroreduction of dioxygen at E1/2) 0.38 V with the final products being an approximate 50% mixture of H2O2 and H2O.

Research paper thumbnail of Cobalt(IV) corroles as catalysts for the electroreduction of O2: Reactions of heterobimetallic dyads containing a face-to-face linked Fe(III) or Mn(III) porphyrin

Journal of Inorganic Biochemistry, 2006

A series of heterobinuclear cofacial porphyrin-corrole dyads containing a Co(IV) corrole linked b... more A series of heterobinuclear cofacial porphyrin-corrole dyads containing a Co(IV) corrole linked by one of four different spacers in a face-to-face arrangement with an Fe(III) or Mn(III) porphyrin have been examined as catalysts for the electroreduction of O 2 to H 2 O and/or H 2 O 2 when adsorbed on the surface of a graphite electrode in air-saturated aqueous solutions containing 1 M HClO 4. The examined compounds are represented as (PCY)M III ClCo IV Cl where P is a porphyrin dianion, C is a corrole trianion and Y is a biphenylene (B), 9,9-dimethylxanthene (X), dibenzofuran (O) or anthracene (A) spacer. The catalytic behavior of the seven investigated dyads in the two heterobimetallic (PCY)MClCoCl series of catalysts is compared on one hand to what was previously reported for related dyads with a single Co(III) corrole macrocycle linked to a free-base porphyrin with the same set of linking bridges, (PCY)H 2 Co, and on the other hand to dicobalt porphyrin-corrole dyads of the form (PCY)Co 2 which were shown to efficiently electrocatalyze the four electron reduction of O 2 at a graphite electrode in acid media. Comparisons between the four series of porphyrin-corrole dyads, (PCY)Co 2 , (PCY)H 2 Co, (PCY)FeClCoCl and (PCY)MnClCoCl, show that in all cases the biscobalt dyads catalyze O 2 electroreduction at potentials more positive by an average 110 mV as compared to the related series of compounds containing a Co(III) or Co(IV) corrole macrocycle linked to a free-base metalloporphyrin or a metalloporphyrin with an Fe(III) or Mn(III) central metal ion. The data indicates that the E 1/2 values where electrocatalysis is initiated is related to the initial site of electron transfer, which is the Co(III)/Co(II) porphyrin reduction process in the case of (PCY)Co 2 and the Co(IV)/Co(III) corrole reduction in the case of (PCY)MnClCoCl, (PCY)FeClCoCl and (PCY)H 2 Co. The overall data also suggests that the catalytically active form of the biscobalt dyad in (PCY)Co 2 contains a Co(II) porphyrin and a Co(IV) corrole.

Research paper thumbnail of Catalytic Activity of Biscobalt Porphyrin-Corrole Dyads Toward the Reduction of Dioxygen

Inorganic Chemistry, 2009

A series of biscobalt cofacial porphyrin-corrole dyads bearing mesityl substituents at the meso p... more A series of biscobalt cofacial porphyrin-corrole dyads bearing mesityl substituents at the meso positions of the corrole ring were investigated as to their electrochemistry, spectroelectrochemistry, and CO binding properties in nonaqueous media and then applied to the surface of a graphite electrode and tested as electrocatalysts for the reduction of dioxygen to water or hydrogen peroxide in air-saturated aqueous solutions containing 1 M HClO(4). The catalytic reduction of O(2) with the same dyads was also investigated in the homogeneous phase using 1,1'-dimethylferrocene as a reductant in PhCN containing HClO(4). The examined compounds are represented as (PMes(2)CY)Co(2), where P = a porphyrin dianion, Mes(2)C = a corrole trianion with two mesityl groups in trans meso-positions of the macrocycle, and Y is one of three bridging groups separating the two metallomacrocycles in a face-to-face arrangement, either with 9,9-dimethylxanthene, dibenzofuran, or diphenylether as linkers. Cyclic voltammetry and rotating disk electrode voltammetry revealed that the examined compounds are all catalytically active toward the electroreduction of dioxygen in acid media giving H(2)O(2) or H(2)O depending upon the type of linkage (Y) and the initial site of electron transfer which, in nonaqueous media, could be switched between the corrole and the porphyrin metal center by variations of substituents on the corrole macrocycle or the gas above the solution. The homogeneous reduction of dioxygen via a two- or four-electron transfer process was also investigated using 1,1'-dimethylferrocene as reductant in PhCN containing HClO(4).

Research paper thumbnail of Electrochemistry, Spectroelectrochemistry, Chloride Binding, and O 2 Catalytic Reactions of Free-Base Porphyrin−Cobalt Corrole Dyads

Inorganic Chemistry, 2005

Three face-to-face linked porphyrin-corrole dyads were investigated as to their electrochemistry,... more 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.

Research paper thumbnail of Clarification of the Oxidation State of Cobalt Corroles in Heterogeneous and Homogeneous Catalytic Reduction of Dioxygen

Inorganic Chemistry, 2008

Co(III) corroles were investigated as efficient catalysts for the reduction of dioxygen in the pr... more Co(III) corroles were investigated as efficient catalysts for the reduction of dioxygen in the presence of perchloric acid in both heterogeneous and homogeneous systems. The investigated compounds are (5,10,15-tris(pentafluorophenyl)corrole)cobalt (TPFCor)Co, (10-pentafluorophenyl-5,15-dimesitylcorrole)cobalt (F 5PhMes 2Cor)Co, and (5,10,15-trismesitylcorrole)cobalt (Mes 3Cor)Co, all of which contain bulky substituents at the three meso positions of the corrole macrocycle. Cyclic voltammetry and rotating ring-disk electrode voltammetry were used to examine the catalytic activity of the compounds when adsorbed on the surface of a graphite electrode in the presence of 1.0 M perchloric acid, and this data is compared to results for the homogeneous catalytic reduction of O 2 in benzonitrile containing 10 (-2) M HClO 4. The corroles were also investigated as to their redox properties in nonaqueous media. A reversible one-electron oxidation occurs at E 1/2 values between 0.42 and 0.89 V versus SCE depending upon the solvent and number of fluorine substituents on the compounds, and this is followed by a second reversible one-electron abstraction at E 1/2 = 0.86 to 1.18 V in CH 2Cl 2, THF, or PhCN. Two reductions of each corrole are also observed in the three solvents. A linear relationship is observed between E 1/2 for oxidation or reduction and the number of electron-withdrawing fluorine groups on the compounds, and the magnitude of the substituent effect is compared to what is observed in the case of tetraphenylporphyrins containing meso -substituted C 6F 5 substituents. The electrochemically generated forms of the corrole can exist with Co(I), Co(II), or Co(IV) central metal ions, and the site of the electron-transfer in each oxidation or reduction of the initial Co(III) complex was examined by UV-vis spectroelectrochemistry. ESR characterization was also used to characterize singly oxidized (F 5PhMes 2Cor)Co, which is unambiguously assigned as a Co(III) radical cation rather than the expected Co(IV) corrole with an unoxidized macrocyclic ring.

Research paper thumbnail of Synthesis, characterization and X-ray crystal structures of cyclam derivatives. 7. Hydrogen-bond induced allosteric effects and protonation cooperativity in a macrotricyclic bisdioxocyclam receptor

New Journal of Chemistry, 2005

Research paper thumbnail of Cobalt(III) Corroles as Electrocatalysts for O2 Reduction: Reactivity of a Monocorrole, Biscorroles, and Porphyrin–Corrole Dyads

Le travail de recherche concerne l'électroreduction catalytique du dioxygène par des complexe... more Le travail de recherche concerne l'électroreduction catalytique du dioxygène par des complexes de cobalt adsorbés à la surface d'électrodes de graphite. Les systèmes bismacrocycliques étudiés se composent soit d'un corrole de cobalt(III) lié à une porphyrine de cobalt(II) soit de deux corroles de cobalt(III) maintenus face-à-face par un espaceur aromatique. En employant des espaceurs rigides tels que l'anthracène (A), le biphenylène (B), le 9,9-dimethylxanthène (X) ou le dibenzofurane (O), il est possible de varier la distance cobalt-cobalt entre les deux unités macrocycliques. L'étude des propriétés catalytiques de ces complexes à l'aide d'une électrode tournante disque-anneau indique que les porphyrin-corroles (PCY)Co2 et les biscorroles (BCY)Co2 (avec Y = A, B, X ou O) catalysent la réduction du dioxygène en eau selon un processus à 4 électrons et 4 protons avec une sélectivité plus élevée par rapport au processus de réduction à 2 électrons conduisant ...

Research paper thumbnail of Cobalt(III) Corroles as Electrocatalysts for the Reduction of Dioxygen:  Reactivity of a Monocorrole, Biscorroles, and Porphyrin−Corrole Dyads

Journal of the American Chemical Society, 2005

Three series of cobalt(III) corroles were tested as catalysts for the electroreduction of dioxyge... more Three series of cobalt(III) corroles were tested as catalysts for the electroreduction of dioxygen to water. One was a simple monocorrole represented as (Me4Ph5Cor)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)Co2, 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)Co2, and the biscorrole complexes, (BCY)Co2, which contain two Co(III) ions in their air-stable forms, all provide a direct four-electron pathway for the reduction of O2 to H2O 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 E1/2 which was located at 0.47 V vs SCE for (PCA)Co2 and 0.39 V vs SCE for (BCA)Co2. The cobalt(III) monocorrole (Me4Ph5Cor)Co also catalyzes the electroreduction of dioxygen at E1/2) 0.38 V with the final products being an approximate 50% mixture of H2O2 and H2O.

Research paper thumbnail of Cobalt(IV) corroles as catalysts for the electroreduction of O2: Reactions of heterobimetallic dyads containing a face-to-face linked Fe(III) or Mn(III) porphyrin

Journal of Inorganic Biochemistry, 2006

A series of heterobinuclear cofacial porphyrin-corrole dyads containing a Co(IV) corrole linked b... more A series of heterobinuclear cofacial porphyrin-corrole dyads containing a Co(IV) corrole linked by one of four different spacers in a face-to-face arrangement with an Fe(III) or Mn(III) porphyrin have been examined as catalysts for the electroreduction of O 2 to H 2 O and/or H 2 O 2 when adsorbed on the surface of a graphite electrode in air-saturated aqueous solutions containing 1 M HClO 4. The examined compounds are represented as (PCY)M III ClCo IV Cl where P is a porphyrin dianion, C is a corrole trianion and Y is a biphenylene (B), 9,9-dimethylxanthene (X), dibenzofuran (O) or anthracene (A) spacer. The catalytic behavior of the seven investigated dyads in the two heterobimetallic (PCY)MClCoCl series of catalysts is compared on one hand to what was previously reported for related dyads with a single Co(III) corrole macrocycle linked to a free-base porphyrin with the same set of linking bridges, (PCY)H 2 Co, and on the other hand to dicobalt porphyrin-corrole dyads of the form (PCY)Co 2 which were shown to efficiently electrocatalyze the four electron reduction of O 2 at a graphite electrode in acid media. Comparisons between the four series of porphyrin-corrole dyads, (PCY)Co 2 , (PCY)H 2 Co, (PCY)FeClCoCl and (PCY)MnClCoCl, show that in all cases the biscobalt dyads catalyze O 2 electroreduction at potentials more positive by an average 110 mV as compared to the related series of compounds containing a Co(III) or Co(IV) corrole macrocycle linked to a free-base metalloporphyrin or a metalloporphyrin with an Fe(III) or Mn(III) central metal ion. The data indicates that the E 1/2 values where electrocatalysis is initiated is related to the initial site of electron transfer, which is the Co(III)/Co(II) porphyrin reduction process in the case of (PCY)Co 2 and the Co(IV)/Co(III) corrole reduction in the case of (PCY)MnClCoCl, (PCY)FeClCoCl and (PCY)H 2 Co. The overall data also suggests that the catalytically active form of the biscobalt dyad in (PCY)Co 2 contains a Co(II) porphyrin and a Co(IV) corrole.

Research paper thumbnail of Catalytic Activity of Biscobalt Porphyrin-Corrole Dyads Toward the Reduction of Dioxygen

Inorganic Chemistry, 2009

A series of biscobalt cofacial porphyrin-corrole dyads bearing mesityl substituents at the meso p... more A series of biscobalt cofacial porphyrin-corrole dyads bearing mesityl substituents at the meso positions of the corrole ring were investigated as to their electrochemistry, spectroelectrochemistry, and CO binding properties in nonaqueous media and then applied to the surface of a graphite electrode and tested as electrocatalysts for the reduction of dioxygen to water or hydrogen peroxide in air-saturated aqueous solutions containing 1 M HClO(4). The catalytic reduction of O(2) with the same dyads was also investigated in the homogeneous phase using 1,1'-dimethylferrocene as a reductant in PhCN containing HClO(4). The examined compounds are represented as (PMes(2)CY)Co(2), where P = a porphyrin dianion, Mes(2)C = a corrole trianion with two mesityl groups in trans meso-positions of the macrocycle, and Y is one of three bridging groups separating the two metallomacrocycles in a face-to-face arrangement, either with 9,9-dimethylxanthene, dibenzofuran, or diphenylether as linkers. Cyclic voltammetry and rotating disk electrode voltammetry revealed that the examined compounds are all catalytically active toward the electroreduction of dioxygen in acid media giving H(2)O(2) or H(2)O depending upon the type of linkage (Y) and the initial site of electron transfer which, in nonaqueous media, could be switched between the corrole and the porphyrin metal center by variations of substituents on the corrole macrocycle or the gas above the solution. The homogeneous reduction of dioxygen via a two- or four-electron transfer process was also investigated using 1,1'-dimethylferrocene as reductant in PhCN containing HClO(4).

Research paper thumbnail of Electrochemistry, Spectroelectrochemistry, Chloride Binding, and O 2 Catalytic Reactions of Free-Base Porphyrin−Cobalt Corrole Dyads

Inorganic Chemistry, 2005

Three face-to-face linked porphyrin-corrole dyads were investigated as to their electrochemistry,... more 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.

Research paper thumbnail of Clarification of the Oxidation State of Cobalt Corroles in Heterogeneous and Homogeneous Catalytic Reduction of Dioxygen

Inorganic Chemistry, 2008

Co(III) corroles were investigated as efficient catalysts for the reduction of dioxygen in the pr... more Co(III) corroles were investigated as efficient catalysts for the reduction of dioxygen in the presence of perchloric acid in both heterogeneous and homogeneous systems. The investigated compounds are (5,10,15-tris(pentafluorophenyl)corrole)cobalt (TPFCor)Co, (10-pentafluorophenyl-5,15-dimesitylcorrole)cobalt (F 5PhMes 2Cor)Co, and (5,10,15-trismesitylcorrole)cobalt (Mes 3Cor)Co, all of which contain bulky substituents at the three meso positions of the corrole macrocycle. Cyclic voltammetry and rotating ring-disk electrode voltammetry were used to examine the catalytic activity of the compounds when adsorbed on the surface of a graphite electrode in the presence of 1.0 M perchloric acid, and this data is compared to results for the homogeneous catalytic reduction of O 2 in benzonitrile containing 10 (-2) M HClO 4. The corroles were also investigated as to their redox properties in nonaqueous media. A reversible one-electron oxidation occurs at E 1/2 values between 0.42 and 0.89 V versus SCE depending upon the solvent and number of fluorine substituents on the compounds, and this is followed by a second reversible one-electron abstraction at E 1/2 = 0.86 to 1.18 V in CH 2Cl 2, THF, or PhCN. Two reductions of each corrole are also observed in the three solvents. A linear relationship is observed between E 1/2 for oxidation or reduction and the number of electron-withdrawing fluorine groups on the compounds, and the magnitude of the substituent effect is compared to what is observed in the case of tetraphenylporphyrins containing meso -substituted C 6F 5 substituents. The electrochemically generated forms of the corrole can exist with Co(I), Co(II), or Co(IV) central metal ions, and the site of the electron-transfer in each oxidation or reduction of the initial Co(III) complex was examined by UV-vis spectroelectrochemistry. ESR characterization was also used to characterize singly oxidized (F 5PhMes 2Cor)Co, which is unambiguously assigned as a Co(III) radical cation rather than the expected Co(IV) corrole with an unoxidized macrocyclic ring.