Photocatalytic generation of a non-heme Fe(III)-hydroperoxo species with O$_2$ in water for oxygen atom transfer reaction
Résumé
Coupling a photoredox module and a bio-inspired non-heme model to activate O$_2$ for oxygen atom transfer (OAT) reaction requires a vigorous investigation to shed light on the multiple competing electron transfer steps, charge accumulation and annihilation processes, and the activation of O$_2$ at the catalytic unit. We found that the efficient oxidative quenching mechanism between [Ru(bpy)$_3$]$^{2+}$ chromophore and a reversible electron mediator, methyl viologen (MV$^{2+}$), to form the reducing species methyl viologen radical (MV$^{•+}$) can convey an electron to O$_2$ to form the uperoxide radical and resetting an Fe(III) species in a catalytic cycle to the Fe(II) state in an aqueous solution. The formation of the Fe(III)-hydroperoxo (Fe$^{III}$ OOH) intermediate therefrom to evolve to highly oxidized iron-oxo species to perform the OAT reaction to an alkene substrate. Such a strategy allows to bypass the challenging task of charge accumulation at the molecular catalytic unit for the two-electron activation of O$_2$. The Fe$^{III}$-OOH catalytic precursor was trapped and characterized by EPR spectroscopy pertaining a metal assisted catalysis. Importantly, we found that the substrate itself can act as the electron donor to reset the photooxidzed chromophore in the initial state closing the photocatalytic loop hence excluding the use of a sacrificial electron donor. Laser Flash Photolysis (LFP) studies and spectroscopic monitoring during photocatalysis lend credence to the proposed catalytic cycle.
Domaines
Chimie
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