Modeling the cis ‐Oxo‐Labile Binding Site Motif of Non‐Heme Iron Oxygenases: Water Exchange and Oxidation Reactivity of a Non‐Heme Iron(IV)‐Oxo Compound Bearing a Tripodal Tetradentate Ligand

The spectroscopic and chemical characterization of a new synthetic non‐heme iron(IV)‐oxo species [Fe IV (O)( Me,H Pytacn)(S)] 2+ ( 2 , Me,H Pytacn=1‐(2′‐pyridylmethyl)‐4,7‐dimethyl‐1,4,7‐triazacyclononane, S=CH 3 CN or H 2 O) is described. Complex 2 was prepared by reaction of [Fe II (CF 3 SO 3 ) 2 ( Me,H Pytacn)] ( 1 ) with peracetic acid. Complex 2 bears a tetradentate N 4 ligand that leaves two cis sites available for binding an oxo group and a second external ligand but, unlike the related iron(IV)‐oxo species with tetradentate ligands, it is remarkably stable at room temperature ( t 1/2 >2 h at 288 K). Its ability to exchange the oxygen atom of the oxo ligand with water has been analyzed in detail by means of kinetic studies, and a mechanism is proposed on the basis of DFT calculations. Hydrogen‐atom abstraction from CH bonds and oxygen‐atom transfer to sulfides by 2 have also been studied. Despite its thermal stability, 2 proves to be a very powerful oxidant that is capable of breaking the strong CH bond of cyclohexane (bond dissociation energy=99.3 kcal mol −1 ).