Abstract
Tridentate 1,3-bis(2 ′ -Ar-imino)isoindolinato manganese(II) complexes were found to efficiently catalyze the mild oxidation of organic sulfides to sulfoxides and benzyl alcohols to benzaldehydes with mCPBA and PhIO, but they proved almost ineffective by the use of tBuOOH and H2O2 at room temperature. The effect of electron-withdrawing and electron-donating substituents on the substrates (thioanisole and benzylalcohol), and the redox properties of the metal center by varying the aryl groups on the bis-iminoisoindoline were investigated, and showed a significant impact on the catalytic C–H oxidation and sulfoxidation reactions. Based on these results, including the linear correlations between the oxidation reactivity of the catalysts and Mn III /Mn II redox potentials, the Hammett correlation with ρ=-0.27 for 4R-PhSMe and ρ=-0.27 for 4R-PhCH2OH, electrophilic oxomanganese(IV) intermediate has been suggested as key oxidant. Furthermore, the small negative slope (-0.5) from the logk rel versus E ox o for 4R-PhSMe gives clear evidence for the direct oxygen atom transfer (OAT) mechanism instead of electron transfer (ET) mechanism between the Mn IV O and PhSMe.
Highlights
High-valent oxoiron species play important roles in both heme and non-heme monooxygenase enzymes and their biomimetic reactions
We have shown earlier that manganese 1,3-bis(2 -Ar-imino)isoindoline complexes can mediate many types of biomimetic redox reactions [12]; including the oxidation of catechols to quinones [13], the oxidative cyclization of 2-aminophenol to phenoxazinone [13], the catalytic disproportionation of hydrogen peroxide [14,15,16], and the dismutation of superoxide radicals [17]
Based on the advantageous properties of the above systems the solubility, electronic structure and steric properties of the ligand as well as their complexes can be further developed by the synthesis of 1,3-bis(2 -Ar-imino)isoindolines, an open-chained phthalocyanine mimic, introducing various aryl groups on the bis-iminoisoindoline moiety [12]
Summary
High-valent oxoiron species play important roles in both heme and non-heme monooxygenase enzymes and their biomimetic reactions. We have shown earlier that manganese 1,3-bis(2 -Ar-imino)isoindoline complexes can mediate many types of biomimetic redox reactions [12]; including the oxidation of catechols to quinones (catechol oxidase) [13], the oxidative cyclization of 2-aminophenol to phenoxazinone (phenoxazinone synthase) [13], the catalytic disproportionation of hydrogen peroxide (catalase) [14,15,16], and the dismutation of superoxide radicals (superoxide dismutase, SOD) [17]. They can ISSN (electronic) : 1878-1543 https://comptes- rendus.academie- sciences.fr/chimie/
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