Earth-Abundant Mixed-Metal Catalysts for Hydrocarbon Oxygenation

James R. Pankhurst, Massimiliano Curcio, Stephen Sproules*, Guy C. Lloyd-Jones, Jason B. Love

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

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.

Original languageEnglish
Pages (from-to)5915-5928
Number of pages14
JournalInorganic Chemistry
Volume57
Issue number10
Early online date30 Apr 2018
DOIs
Publication statusPublished - 21 May 2018

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