title: A mechanistic study of the reaction between a diiron(II) complex [FeII(2)(mu-OH)2(6-Me3-TPA)2](2+) and O2 to form a diiron(III) peroxo complex.
abstract: A kinetic study of the reaction between a diiron(II) complex [Fe(II)(2)(mu-OH)(2)(6-Me(3)-TPA)(2)](2+) 1, where 6-Me(3)-TPA = tris(6-methyl-2-pyridylmethyl)amine, and dioxygen is presented. A diiron(III) peroxo complex [Fe(III)(2)(mu-O)(mu-O(2))(6-Me(3)-TPA)(2)](2+) 2 forms quantitatively in dichloromethane at temperatures from -80 to -40 degrees C. The reaction is first order in [Fe(II)(2)] and [O(2)], with the activation parameters DeltaH(double dagger) = 17 +/- 2 kJ mol(-1) and DeltaS(double dagger) = -175 +/- 20 J mol(-1) K(-1). The reaction rate is not significantly influenced by the addition of H(2)O or D(2)O. The reaction proceeds faster in more polar solvents (acetone and acetonitrile), but the yield of 2 is not quantitative in these solvents. Complex 1 reacts with NO at a rate about 10(3) faster than with O(2). The mechanistic analysis suggests an associative rate-limiting step for the oxygenation of 1, similar to that for stearoyl-ACP Delta(9)-desaturase, but distinct from the probable dissociative pathway of methane monoxygenase. An eta(1)-superoxo Fe(II)Fe(III) species is a likely steady-state intermediate during the oxygenation of complex 1.
authors.affiliation: Department of Chemistry, Tufts University, Medford, MA 02155, USA.
authors.forename: S V
authors.initials: SV
authors.lastname: Kryatov
authors.forename: E V
authors.initials: EV
authors.lastname: Rybak-Akimova
authors.forename: V L
authors.initials: VL
authors.lastname: MacMurdo
authors.forename: L
authors.initials: L
authors.lastname: Que
mesh_terms: D000465:Algorithms; D005296:Ferrous Compounds / Q000737:chemistry*; D007700:Kinetics; D008752:Methylene Chloride; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry*; D013696:Temperature
chemical_list: C430763:Fe(II)(2)(mu-OH)2(6-Me3-TPA)2; D005296:Ferrous Compounds; D008752:Methylene Chloride; D010100:Oxygen