Spectroelectrochemical characterization of meso triaryl-substituted Mn(IV), Mn(III) and Mn(II) corroles. Effect of solvent and oxidation state on UV-visible spectra and redox potentials in nonaqueous media

Abstract

Two series of substituted manganese triarylcorroles were synthesized and characterized as to their electrochemical and spectroelectrochemical properties in CH 2 Cl 2, CH 3 CN and pyridine. The investigated compounds are represented as ( YPh )3 CorMn III and ( YPh )3 CorMn IV Cl , where Cor is a trianion of the corrole and Y is a Cl , F , H or CH 3 para-substituent on the three phenyl rings of the macrocycle. Each neutral Mn(III) corrole exists as a four-coordinate complex in CH 2 Cl 2 and CH 3 CN and as a five-coordinate species in pyridine. ( YPh )3 CorMn III undergoes two oxidations to stepwise generate a Mn(IV) corrole and a Mn(IV) π-cation radical. It also undergoes one reduction to generate a Mn(II) corrole in CH 2 Cl 2 or CH 3 CN . In contrast, the reduction of ( YPh )3 CorMn III leads to a Mn(III) corrole π-anion radical in pyridine. One oxidation is observed for ( YPh )3 CorMn IV Cl in CH 2 Cl 2 and CH 3 CN to generate a Mn(IV) corrole π-cation radical while Mn(III) and Mn(II) corroles are stepwise formed after reduction of the same compound. The second reduction of ( YPh )3 CorMn IV Cl in pyridine gives a Mn(III) π-anion radical as opposed to a Mn(II) corrole with an unreduced π-ring system. The neutral, reduced and oxidized forms of each corrole were characterized by electrochemistry and UV-visible spectroelectrochemistry and comparisons are made between the UV-visible spectra and redox potentials of the compounds in different central metal oxidation states. An overall reduction/oxidation mechanism in the three solvents is proposed.

Electrocatalytic Reduction of CO2 to Acetic Acid by a Molecular Manganese Corrole Complex

“…The first metal centered oxidation at E 1/2 =0.68 V and E 1/2 =0.96 V vs. NHE of Mn III to Mn IV is split into two waves, where the current of the first redox couple is significantly smaller than of the second one. Similar redox behavior for other triaryl‐corroles was found by Kadish and co‐workers . This split redox‐waves is a result of two different Mn IV species that can be formed, an ion pair with the anion of the electrolyte salt (Mn IV PF 6 ) and the Mn IV+ cation species .…”

“…Similar redox behavior for other triaryl‐corroles was found by Kadish and co‐workers . This split redox‐waves is a result of two different Mn IV species that can be formed, an ion pair with the anion of the electrolyte salt (Mn IV PF 6 ) and the Mn IV+ cation species . The second oxidation at E p =1.45 V vs. NHE is ring‐centered where Mn IV is oxidized to a Mn IV π radical cation .…”

“…The electrochemical properties of 0.8 mm Mn-corrole in acetonitrile were investigated via cyclic voltammetry measurements using glassy carbon as working electrode with 0.1m TBAPF 6 as supporting electrolyte at a scan rate of 100 mV s À1 . In the cathodic part, two one electron reductions at E 1/2 = À0.94 V vs. NHE (Mn III /Mn II ) and E pc = À1.60 V vs. NHE are shown in Figure 1 B and Figure S10, where the first redox couple is reversible [14,19] whereas the second one is irreversible. Corresponding electro paramagnetic resonance (EPR) measurements, suggest the formation of a Mn II radical anion at À1.60 V ( Figure S11).…”

“…[14,19] This split redox-waves is a result of two different Mn IV species that can be formed, an ion pair with the anion of the electrolyte salt (Mn IV PF 6 ) and the Mn IV+ cation species. [14,19] The second oxidation at E p = 1.45 V vs. NHE is ring-centered where Mn IV is oxidized to a Mn IV p radical cation. [14] We further studied the influence of water under CO 2 in the electrochemical system.…”

Electrocatalytic Reduction of CO2 to Acetic Acid by a Molecular Manganese Corrole Complex

“…The electrochemical properties of 0.8 m m Mn‐corrole in acetonitrile were investigated via cyclic voltammetry measurements using glassy carbon as working electrode with 0.1 m TBAPF 6 as supporting electrolyte at a scan rate of 100 mV s −1 . In the cathodic part, two one electron reductions at E 1/2 =−0.94 V vs. NHE (Mn III /Mn II ) and E pc =−1.60 V vs. NHE are shown in Figure B and Figure S10, where the first redox couple is reversible whereas the second one is irreversible. Corresponding electro paramagnetic resonance (EPR) measurements, suggest the formation of a Mn II radical anion at −1.60 V (Figure S11).…”