A di‑iron(III) μ-oxido complex as catalyst precursor in the oxidation of alkanes and alkenes

Abstract

The oxido-bridged diiron(III) complex [Fe₂(μ-O)(μ-OAc)(DPEAMP)₂](OCH₃) (1), based on a new unsymmetrical ligand with an N₄O donor set, viz. [2-((bis(pyridin-2-ylmethyl)amino)methyl)-6-((ethylamino)methyl)-4-methylphenol (HDPEAMP)], has been prepared and characterized by spectroscopic methods and X-ray crystallography. The crystal structure of the complex reveals that each Fe(III) ion is coordinated by three nitrogen and three oxygen donors, two of which are the bridging oxido and acetate ligands. Employing H₂O₂ as a terminal oxidant, 1 is capable of oxidizing a number of alkanes and alkenes with high activity. The catalytic oxidation of 1,2-dimethylcyclohexane results in excellent retention of configuration. Monitoring of the reaction of 1 with H₂O₂ and acetic acid in the absence of substrate, using low-temperature UV-Vis spectroscopy, suggests the in situ formation of a transient Fe(III)₂-peroxido species. While the selectivity and nature of oxidation products implicate a high-valent iron-oxido complex as a key intermediate, the low alcohol/ketone ratios suggest a simultaneous radical-based process.

Keywords: Catalysis; Epoxidation; Hydroxylation; Iron; Metal-oxido complex; Peroxide complex.