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

A novel hydroperoxoiron(III) species [Fe III (OOH)(MeCN)(PyNMe 3 )] 2+ (3) has been generated by reaction of its ferrous precursor [Fe II (CF 3 SO 3 ) 2 (PyNMe 3 )] (1) 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, 3 behaves as a sluggish oxidant and it is not kinetically competent for breaking weak C−H bonds. However, triflic acid addition to 3 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 . )Fe IV (O)] (Compound I) Financial support for this work was provided by the European Commission (2011-CIG-303522 to A.C., 675020-MSCA-ITN-2015-ETN to M.C.), the Spanish Ministry of Science (CTQ2015-70795-P to M.C., CTQ2016-77989-P to A.C., CTQ2014-52525-P to J.M.L., CTQ2015-65707-C2-2-P to M.G.B., and CSD2010-00065 to M.C and M.G.B.) and Generalitat de Catalunya (ICREA Academia Award to M.C. and 2014 SGR 862). The Spanish Ministry of Science is also acknowledged for a Ram n y Cajal contract to A.C. (RYC-2011–08683). The work conducted at the University of Minnesota has been supported by the US National Science Foundation (grant CHE1665391 to L.Q.). XAS data was collected at the SOLEIL synchrotron SAMBA beamline (proposal 20150413)