Mechanistic Insights into Ru‐catalyzed Alkene Epoxidation with Nitrous Oxide as a Terminal Oxidant

Simple kinetic studies provided insights to inform future catalyst designs able to employ N₂O as an oxidant under mild conditions. Results suggest the use of low alkene concentrations, possible saturation behavior at high N₂O pressures and a potential catalyst turnover involving disproportionation of Ru^IV(O) and Ru^IV(O)(N₂O).

Abstract

Nitrous oxide (N₂O) is a greenhouse gas produced in the manufacture of 6,6-nylon and nitric acid. While an attractive oxidant that releases only N₂ as a by-product, the kinetic stability of N₂O typically requires high temperatures and pressures for activation. This work describes initial kinetics of oxygen transfer in the epoxidation of cholesteryl acetate with N₂O catalysed by D₄ -Ru(VI)(por)(O)₂ complexes in efforts to provide a better mechanistic understanding of this chemistry. Insights include a need for low concentrations of the alkene to avoid competitive binding to the metal, possible saturation behavior at high N₂O pressures, transfer of only one oxygen of Ru^VI(O)₂ to substrate and a possible catalyst turnover involving disproportionation of Ru^IV(O) and Ru^IV(O)(N₂O) to active Ru^VI(O)₂, Ru^IV(O) and N₂. These insights will be used in future designs of improved catalysts and reaction protocols that may operate efficiently at low pressures of N₂O and ambident temperature.

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