SET and HAT/PCET Acid-mediated Oxidation Processes in Helical Shaped Fused Bis-phenothiazines

Overview

Journal Chemphyschem

Specialty Chemistry

Date 2021 May 25

PMID 34033195

Citations 6

Authors

Riccardo Amorati

Luca Valgimigli

Andrea Baschieri

Yafang Guo

Fabio Mollica

Stefano Menichetti

Michela Lupi

Caterina Viglianisi

Affiliations

Soon will be listed here.

Abstract

Helical shaped fused bis-phenothiazines 1-9 have been prepared and their red-ox behaviour quantitatively studied. Helicene radical cations (Hel ) can be obtained either by UV-irradiation in the presence of PhCl or by chemical oxidation. The latter process is extremely sensitive to the presence of acids in the medium with molecular oxygen becoming a good single electron transfer (SET) oxidant. The reaction of hydroxy substituted helicenes 5-9 with peroxyl radicals (ROO ) occurs with a 'classical' HAT process giving HelO radicals with kinetics depending upon the substitution pattern of the aromatic rings. In the presence of acetic acid, a fast medium-promoted proton-coupled electron transfer (PCET) process takes place with formation of HelO radicals possibly also via a helicene radical cation intermediate. Remarkably, also helicenes 1-4, lacking phenoxyl groups, in the presence of acetic acid react with peroxyl radicals through a medium-promoted PCET mechanism with formation of the radical cations Hel . Along with the synthesis, EPR studies of radicals and radical cations, BDE of Hel-OH group (BDE ), and kinetic constants (k ) of the reactions with ROO species of helicenes 1-9 have been measured and calculated to afford a complete rationalization of the redox behaviour of these appealing chiral compounds.

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