Spectroscopic and crystallographic characterization of peroxo- and oxoiron complexes.

Abstract

Nonheme oxygen activating enzymes are found as both diiron and monoiron complexes. Prior to undertaking substrate oxidation, many diiron enzymes produce (-peroxo)diiron(III) intermediates, while the catalytically important oxidant found in most monoiron enzymatic cycles is an oxoiron(IV) moiety. Synthetic chemists design small molecules to serve as models for study of these transient species. This work is intended to supplement what is known about both synthetic (-peroxo)diiron(III) and oxoiron(IV) complexes. A series of diiron(II) compounds was synthesized and reacted with oxygen. Through ligand rearrangements, some of the resultant (-1:1-peroxo)diiron(III) species initially observed converted to secondary (-1:1-peroxo)diiron(III) intermediates exhibiting spectroscopic features akin to complexes already known. The identities of oxyanion bridges present in the diiron(II) precursors drastically affected the stability of the (-1:1-peroxo)diiron(III) species initially produced upon oxygenation. Upon decay, compounds of this type putatively produce tetranuclear iron(III) clusters. A set of these clusters was synthesized and examined via x-ray crystallography. Also, a new method was developed for examining oxoiron(IV) intermediates using resonance Raman spectroscopy. Synthetic complexes are often used as models for biological systems. A thorough understanding of these models may lead to catalytic systems usable on an industrial scale. Please see pdf abstract for correct chemical symbols.