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

• Published in: Chemistry : a European journal Vol. 17; no. 5; pp. 1622 - 1634
• Main Authors: Company, Anna, Prat, Irene, Frisch, Jonathan R., Mas-Ballesté, Dr Ruben, Güell, Mireia, Juhász, Gergely, Ribas, Xavi, Münck, Dr Eckard, Luis, Josep M., Que Jr, Lawrence, Costas, Miquel
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.02.2011; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Binding; Binding Sites; bioinorganic chemistry; Chemistry; Crystallography, X-Ray; Exchange; Heme - chemistry; Iron; Iron - chemistry; Iron and steel industry; Iron Compounds - chemistry; Ligands; Mathematical models; Models, Chemical; Molecular Structure; Oxidants; Oxidants - chemistry; Oxidation-Reduction; oxygenases; Oxygenases - chemistry; reaction mechanisms; tetradentate ligands; Thermodynamics
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201002297

The spectroscopic and chemical characterization of a new synthetic non‐heme iron(IV)‐oxo species [FeIV(O)(Me,HPytacn)(S)]2+ (2, Me,HPytacn=1‐(2′‐pyridylmethyl)‐4,7‐dimethyl‐1,4,7‐triazacyclononane, S=CH3CN or H2O) is described. Complex 2 was prepared by reaction of [FeII(CF3SO3)2(Me,HPytacn)] (1) with peracetic acid. Complex 2 bears a tetradentate N4 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 (t1/2>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 ion from CH 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 CH bond of cyclohexane (bond dissociation energy=99.3 kcal mol−1). A powerful oxidant: A non‐heme oxo‐iron(IV) complex (see picture), containing a labile site cis to the terminal oxo group, has been prepared and characterized. The complex is unusually stable (t1/2>2 h at 288 K). Water exchange, oxo transfer, and H ion reactions have been studied. Despite its thermal stability, the complex is a very powerful oxidant.