Mechanistic Studies of the Formation and Decay of Diiron(III) Peroxo Complexes in the Reaction of Diiron(II) Precursors with Dioxygen.
Mechanistic studies of the reactions of three analogous alkoxo-bridged diiron(II) complexes with O(2) have been carried out. The compounds, which differ primarily in the steric accessibility of dioxygen to the diiron(II) center, form metastable &mgr;-peroxo intermediates when studied at low temperature. At ambient temperatures, these intermediates decay to form (&mgr;-oxo)polyiron(III) products. The effect of ligand steric constraints on the O(2) reactivity was investigated. When access to the diiron center was unimpeded, the reaction was first-order with respect to both [Fe(II)(2)] and [O(2)] and the activation parameters for O(2) addition were similar to those for O(2) reacting with the dioxygen transport protein hemerythrin. When the binding site was occluded, however, reduced order with respect to [O(2)] was observed and a two-step mechanism was required to explain the kinetic results. Decay of all three peroxide intermediates involves a bimolecular event, implying the formation of tetranuclear species in the transition state.
Feig
Andrew L.
AL
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, and Institute for Inorganic Chemistry, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058 Erlangen, Germany.
Becker
Michael
M
Schindler
Siegfried
S
van Eldik
Rudi
R
Lippard
Stephen J.
SJ