Oxidation of olefins using molecular oxygen catalyzed by a part per million level of recyclable copper catalyst under mild conditions

Abstract

Copper catalysts with an imidazole salt tag ([Cu-Imace-R-H][X], X⁻ = F⁻, Cl⁻, Br⁻, I⁻, CF₃CO₂⁻, HSO₄⁻, NO₃⁻, PF₆⁻ or BF₄⁻; R = H or CH₃) show quite high reactivity for the oxidation of non-aromatic olefins with good selectivity for epoxides. The reactions perform well with a part per million (ppm) catalyst loading at mild temperature and ambient pressure. The highest turnover frequency (TOF) reaches up to 900 000 h⁻¹. The catalytic activity is easy to control by changing the anion of [Cu-Imace-R-H][X]. This catalyst is effective for a series of substrates, including internal and terminal olefins, tri- and tetra-substituted olefins and aromatic olefins. In addition, the copper catalyst can be conveniently separated from the reaction system and reused for at least six cycles without any obvious loss of catalytic activity.