Earth-abundant mixed-metal catalysts for hydrocarbon oxygenation

Pankhurst, J. R., Curcio, M., Sproules, S. , Lloyd-Jones, G. C. and Love, J. B. (2018) Earth-abundant mixed-metal catalysts for hydrocarbon oxygenation. Inorganic Chemistry, 57(10), pp. 5915-5928. (doi: 10.1021/acs.inorgchem.8b00420) (PMID:29708740)

Abstract

The oxygenation of aliphatic and aromatic hydrocarbons using earth-abundant Fe and Cu catalysts and “green” oxidants such as hydrogen peroxide is becoming increasingly important to atom-economical chemical processing. In light of this, we describe that dinuclear CuII complexes of pyrrolic Schiff-base macrocycles, in combination with ferric chloride (FeCl3), catalyze the oxygenation of π-activated benzylic substrates with hydroperoxide oxidants at room temperature and low loadings, representing a novel design in oxidation catalysis. Mass spectrometry and extended X-ray absorption fine structure analysis indicate that a cooperative action between CuII and FeIII occurs, most likely because of the interaction of FeCl3 or FeCl4– with the dinuclear CuII macrocycle. Voltammetric measurements highlight a modulation of both CuII and FeIII redox potentials in this adduct, but electron paramagnetic resonance spectroscopy indicates that any Cu–Fe intermetallic interaction is weak. High ketone/alcohol product ratios, a small reaction constant (Hammett analysis), and small kinetic isotope effect for H-atom abstraction point toward a free-radical reaction. However, the lack of reactivity with cyclohexane, oxidation of 9,10-dihydroanthracene, oxygenation by the hydroperoxide MPPH (radical mechanistic probe), and oxygenation in dinitrogen-purge experiments indicate a metal-based reaction. Through detailed reaction monitoring and associated kinetic modeling, a network of oxidation pathways is proposed that includes “well-disguised” radical chemistry via the formation of metal-associated radical intermediates.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Sproules, Dr Stephen
• Authors: Pankhurst, J. R., Curcio, M., Sproules, S., Lloyd-Jones, G. C., and Love, J. B.
• College/School: College of Science and Engineering > School of Chemistry
• Journal Name: Inorganic Chemistry
• Publisher: American Chemical Society
• ISSN: 0020-1669
• ISSN (Online): 1520-510X
• Published Online: 30 April 2018
• Copyright Holders: Copyright © 2018 American Chemical Society
• First Published: First published in Inorganic Chemistry 57(10): 5915-5928
• Publisher Policy: Reproduced in accordance with the copyright policy of the publisher