Altering the Site of Electron Abstraction in Cobalt Corroles <i>via meso</i>-Trifluoromethyl Substituents
W. Ryan Osterloh, Nicolas Desbois, Paul Fleurat‐Lessard, Yuanyuan Fang, Claude P. Gros, Karl M. Kadish
Abstract
A mono-DMSO cobalt meso -CF 3 corrole, formulated as (CF 3 ) 3 CorCo(DMSO), where (CF 3 ) 3 Cor is the trianion of 5,10,15-tris(trifluoromethyl)corrole, was synthesized and characterized as to its spectral and electrochemical properties in nonaqueous media with a focus on its coordination chemistry and electronic structure. Cyclic voltammetric measurements showed more facile reductions and difficult oxidations compared to the cobalt triarylcorrole possessing p -CF 3 Ph units at the meso -positions, a result consistent with the enhanced inductive effect of the electron-withdrawing trifluoromethyl substituents linked directly at the meso -carbon atoms of the macrocycle. The effects of DMSO, pyridine, and cyanide anions (CN – ) on the electrochemistry and spectral properties of the compound were investigated, and it was found that only two molar equivalents are needed to form the bis-CN adduct, which exhibited two 1-electron oxidations at 0.27 and 0.95 V vs saturated calomel electrode (SCE) in CH 2 Cl 2 /0.1 M TBAP. The sites of electron transfer in the first oxidation and reduction were investigated by spectroelectrochemistry and confirmed that the first electron addition affords a Cor 3– Co II complex under all solution conditions independent of the initial coordination and/or electronic configuration ( i.e ., innocent Cor 3– Co III or noninnocent Cor •2– Co II ). In contrast, data for the first oxidation suggests that the site of electron abstraction (ligand or metal) depended upon coordination of the neutral and in situ generated complexes under the various solution conditions, leading to a Co(IV)-corrole 3– product for both the bis-pyridine and bis-cyanide adducts.