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

Abstract

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.

Hydrogen peroxide as a sustainable energy carrier: Electrocatalytic production of hydrogen peroxide and the fuel cell

“…When a monomeric cobalt corrole ([10-pentafluorophenyl-5,15-dimesityl-corrole]cobalt complex, Co(F 5 PhMes 2 Cor), was employed as an electrocatalyst for the reduction of O 2 , the slope of the Koutecky-Levich plot shows that the catalytic electroreduction of O 2 is a pure two-electron process to produce H 2 O 2 [52]. The catalytic process employing Co(F 5 PhMes 2 Cor) was confirmed for the homogeneous phase using Fe(C 5 H 4 Me) 2 as a reductant in PhCN solvent [52].…”

“…The catalytic process employing Co(F 5 PhMes 2 Cor) was confirmed for the homogeneous phase using Fe(C 5 H 4 Me) 2 as a reductant in PhCN solvent [52]. Electron transfer from Fe(C 5 H 4 Me) 2 ( E ox = 0.26 V vs. SCE) to [Co(F 5 PhMes 2 Cor)] + ( E red = 0.38 V) [53] occurs efficiently to produce [Fe(C 5 H 4 Me) 2 ] + and Co(F 5 PhMes 2 Cor) [52]. The cobalt(III) corrole complex, Co(F 5 PhMes 2 Cor), can reduce O 2 in the presence of HClO 4 .…”

Synthesis, characterization and solvent/structural effects on spectral and redox properties of cobalt triphenylcorroles in nonaqueous media

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Corroles and metallocorroles have attracted a great deal of interest in recent years [1][2][3][4][5][6][7][8], in part because of improved synthetic methods which make them more readily available than in the past [1,2,6,7] and in part because these compounds have potential applications as catalysts for a variety of reactions [4,[9][10][11][12][13][14][15][16][17][18][19][20][21][22]. One of the most frequently studied groups of metallocorroles are the cobalt derivatives which have been characterized as to their spectral and electrochemical properties under many different solution conditions [1,2,6,[23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]

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Electrochemistry of Fe(IV) and Mn(IV) corroles containing meso-dichlorophenyl substituents and the use of these compounds as catalysts for the electroreduction of dioxygen in acid media

“…We have earlier examined numerous cobalt triarylcorroles 16,17,19,24,25 phenyl rings of a triarylcorrole will significantly affect the catalytic activity of these compounds towards the reduction of O 2 .…”

“…24,25 However, it was not known if triarylcorroles containing manganese and iron central metal ions would be affected by steric hindrance of the phenyl ring substituents. This is addressed in the present work where 2 newly synthesized Mn(IV) and Fe(IV) corroles having bulky Cl substituents on the ortho-position of the phenyl rings are examined as to their catalytic activity for the electoreduction of O 2 at an edge-plane pyrolytic graphite electrode in 1.0 M HClO 4 .…”