Sulfur-stabilised copper nanoparticles for the aerobic oxidation of amines to imines under ambient conditions

DÍAZ-REYES, GLORIA; ALONSO, FRANCISCO; SLOAN, GEORGE; MARTÍN-GARCÍA, IRIS; MOGLIE, YANINA

Journal of Materials Chemistry A

Royal Society of Chemistry

Año: 2021 vol. 9 p. 11312 - 11322

2050-7488

The stabilisation of metal nanoparticles and control of their oxidation state are crucial factors in nanocatalysis. Elemental sulfur has been found to be a cheap and effective stabilising agent for copper nanoparticles in the form of copper(i) oxide. The Cu2ONPs/S8 system has been characterised by ICP-OES, EDX, XRD, XPS, FE-SEM, SEM, TEM and Cryo-EM. Astonishingly, in organic medium, the copper nanoparticles are organised as concentric rings within nanodroplets of sulfur of ca. 20-70 nm. In synthetic organic chemistry, imines can be directly obtained by the less studied and practiced oxidation of primary amines; however, the reaction conditions utilised are usually harsh and far from meeting the principles of Green Chemistry. Cu2ONPs/S8 has been successfully applied to the solvent-free aerobic oxidation of primary amines to imines under ambient conditions, using air as a terminal oxidant. The catalyst is effective in the homo- and heterocoupling of benzylic amines at very low copper loading (0.3 mol%), being catalytically superior to a range of commercial copper catalysts. A reaction mechanism has been proposed based on experimental evidence, which clarifies the major uncertainty regarding the key intermediate. The results of this study suggest a number of new avenues for research in nanocatalysis. This journal is