title: Iron(II) complexes supported by sulfonamido tripodal ligands: endogenous versus exogenous substrate oxidation.
abstract: High-valent iron species are known to act as powerful oxidants in both natural and synthetic systems. While biological enzymes have evolved to prevent self-oxidation by these highly reactive species, development of organic ligand frameworks that are capable of supporting a high-valent iron center remains a challenge in synthetic chemistry. We describe here the reactivity of an Fe(II) complex that is supported by a tripodal sulfonamide ligand with both dioxygen and an oxygen-atom transfer reagent, 4-methylmorpholine-N-oxide (NMO). An Fe(III)-hydroxide complex is obtained from reaction with dioxygen, while NMO gives an Fe(III)-alkoxide product resulting from activation of a C-H bond of the ligand. Inclusion of Ca(2+) ions in the reaction with NMO prevented this ligand activation and resulted in isolation of an Fe(III)-hydroxide complex in which the Ca(2+) ion is coordinated to the tripodal sulfonamide ligand and the hydroxo ligand. Modification of the ligand allowed the Fe(III)-hydroxide complex to be isolated from NMO in the absence of Ca(2+) ions, and a C-H bond of an external substrate could be activated during the reaction. This study highlights the importance of robust ligand design in the development of synthetic catalysts that utilize a high-valent iron center.
authors.affiliation: Department of Chemistry, University of California-Irvine , 1102 Natural Sciences II, Irvine, California 92697, United States.
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Cook
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Ziller
authors.forename: A S
authors.initials: AS
authors.lastname: Borovik
mesh_terms: D018360:Crystallography, X-Ray; D003497:Cyclic N-Oxides / Q000737:chemistry*; D005296:Ferrous Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D009025:Morpholines / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D013449:Sulfonamides / Q000737:chemistry*
chemical_list: D003497:Cyclic N-Oxides; D005296:Ferrous Compounds; D008024:Ligands; D009025:Morpholines; D013449:Sulfonamides; C067960:4-methylmorpholine N-oxide; D010100:Oxygen