Acid‐Triggered O−O Bond Heterolysis of a Nonheme FeIII(OOH) Species for the Stereospecific Hydroxylation of Strong C−H Bonds.

Abstract: A novel hydroperoxoiron(III) species [FeIII(OOH)(MeCN)(PyNMe3)]2+ (<bold>3</bold>) has been generated by reaction of its ferrous precursor [FeII(CF3SO3)2(PyNMe3)] (<bold>1</bold>) with hydrogen peroxide at low temperatures. This species has been characterized by several spectroscopic techniques and cryospray mass spectrometry. Similar to most of the previously described low‐spin hydroperoxoiron(III) compounds, <bold>3</bold> behaves as a sluggish oxidant and it is not kinetically competent for breaking weak C−H bonds. However, triflic acid addition to <bold>3</bold> causes its transformation into a much more reactive compound towards organic substrates that is capable of oxidizing unactivated C−H bonds with high stereospecificity. Stopped‐flow kinetic analyses and theoretical studies provide a rationale for the observed chemistry, a triflic‐acid‐assisted heterolytic cleavage of the O−O bond to form a putative strongly oxidizing oxoiron(V) species. This mechanism is reminiscent to that observed in heme systems, where protonation of the hydroperoxo intermediate leads to the formation of the high‐valent [(Porph.)FeIV(O)] (Compound I). [ABSTRACT FROM AUTHOR]