title: Water-Soluble Iron(IV)-Oxo Complexes Supported by Pentapyridine Ligands: Axial Ligand Effects on Hydrogen Atom and Oxygen Atom Transfer Reactivity.
abstract: We report the photochemical generation and study of a family of water-soluble iron(IV)-oxo complexes supported by pentapyridine PY5Me2-X ligands (PY5Me2 = 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine; X = CF3, H, Me, or NMe2), in which the oxidative reactivity of these ferryl species correlates with the electronic properties of the axial pyridine ligand. Synthesis of a systematic series of [Fe(II)(L)(PY5Me2-X)](2+) complexes, where L = CH3CN or H2O, and characterizations by several methods, including X-ray crystallography, cyclic voltammetry, and Mössbauer spectroscopy, show that increasing the electron-donating ability of the axial pyridine ligand tracks with less positive Fe(III)/Fe(II) reduction potentials and quadrupole splitting parameters. The Fe(II) precursors are readily oxidized to their Fe(IV)-oxo counterparts using either chemical outer-sphere oxidants such as CAN (ceric ammonium nitrate) or flash-quench photochemical oxidation with [Ru(bpy)3](2+) as a photosensitizer and K2S2O8 as a quencher. The Fe(IV)-oxo complexes are capable of oxidizing the C-H bonds of alkane (4-ethylbenzenesulfonate) and alcohol (benzyl alcohol) substrates via hydrogen atom transfer (HAT) and an olefin (4-styrenesulfonate) substrate by oxygen atom transfer (OAT). The [Fe(IV)(O)(PY5Me2-X)](2+) derivatives with electron-poor axial ligands show faster rates of HAT and OAT compared to their counterparts supported by electron-rich axial donors, but the magnitudes of these differences are relatively modest.
authors.forename: Teera
authors.initials: T
authors.lastname: Chantarojsiri
authors.affiliation: #Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States.
authors.forename: Yujie
authors.initials: Y
authors.lastname: Sun
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Long
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Chang
mesh_terms: D019905:Benzyl Alcohol / Q000737:chemistry; D018360:Crystallography, X-Ray; D005290:Ferric Compounds / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry; D008024:Ligands; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D010777:Photochemistry / Q000379:methods; D011725:Pyridines / Q000737:chemistry*; D012995:Solubility; D015204:Spectroscopy, Mossbauer; D014867:Water
chemical_list: D005290:Ferric Compounds; D008024:Ligands; D011725:Pyridines; D014867:Water; D006859:Hydrogen; D019905:Benzyl Alcohol; C023666:pyridine; D010100:Oxygen