Conversion of high-spin iron(III)–alkylperoxo toiron(IV)–oxo species via O–O bond homolysis innonheme iron models†

International audienceThe mechanism of the alkylperoxo O–O bond cleavage of low-spin iron(III)–alkylperoxo species has beenwell established in nonheme iron models. In contrast, the alkylperoxo O–O bond cleavage in nonhemehigh-spin iron(III)–alkylperoxo species binding an axial ligand has yet to be elucidated. Herein, we reportthe synthesis and characterization of mononuclear nonheme high-spin iron(III)–alkylperoxo complexeseach bearing an N-tetramethylated 13-membered macrocyclic ligand (13-TMC), [FeIII(OOC(CH3)3)-(13-TMC)]2+ and [FeIII(OOC(CH3)2C6H5)(13-TMC)]2+. The high-spin iron(III)–alkylperoxo complexes wereconverted to an iron(IV)–oxo complex at a fast rate upon addition of thiocyanate (NCS) via theformation of a short-lived intermediate. This intermediate was identified as a high-spin iron(III)–alkylperoxo complex binding a thiocyanate ion as an axial ligand by characterizing it with variousspectroscopic methods and density functional theory (DFT) calculations. We have also provided strongevidence that conversion of the high-spin iron(III)–alkylperoxo complex to its corresponding iron(IV)–oxocomplex occurs via O–O bond homolysis. Thus, we have concluded that the role of the axial ligandbinding to a high-spin iron(III)–alkylperoxo complex is to facilitate the alkylperoxo O–O bond cleavagevia the “push effect”, which has been well established in heme enzymes. To the best of our knowledge,the present study reports the first clear example showing the O–O bond homolysis of a high-spiniron(III)–alkylperoxo complex and the axial ligand effect on the alkylperoxo O–O bond cleavage innonheme iron models