Over 20000-fold activation of a S = 1 Nonheme Iron(IV)Oxo Complex for C-H bond cleavage Reaction in a Tris Imidazole methylamine (TMIMA) ligand backbone

Our recent findings discovered that the spin state is not the only factor for determining the reactivity of iron oxo complexes. To shed more light on this context, we introduced the closest biomimetic Imidazole as a ligand. We have prepared tris (N-methyl imidazole) Amine (TMIMA) and prepared the corresponding Fe(II) complexes using iron(II) triflate and characterized by Single Crystal X-ray. Treatment of 1 (TMIMA)(MeCN)FeII(OTf)2 with (tBuSO2)C6H4IO (ArIO) at −40 °C in MeCN leads to the formation of highly reactive intermediates 2 (t1/2 ~ 4 min, −80°C in Acetone/MeCN(8:2)), which exhibit weak bands at 750 nm (εM = 250 M−1 cm−1) and oxidize a range of hydrocarbons at −40°C in MeCN. Intermediate 2 is the most reactive oxoiron(IV) complex found to date for the oxidation of C–H bonds in the tripodal family and reacts almost one order of magnitude as fast as the S = 2 [FeIV(O)(TQA)(NCMe)]2+ and S = 1 [FeIV(O)(Me3NTB)(NCMe)]2+. In addition, 2 exhibits a C−H/D kinetic isotope effect of 50 for toluene oxidation, showing that C−H bond cleavage is the rate-determining step.