Chemists developed an atomically dispersed copper photocatalyst capable of selectively cleaving methyl and alkyl groups from tertiary amines under visible light, according to research published in Nature Communications. The material, composed of isolated copper single sites anchored on functionalized graphitic carbon nitride, offers a noble-metal-free and recyclable alternative to conventional precious-metal catalysts.
The catalytic process operates under 390-nanometer light irradiation and an oxygen atmosphere. In benchmark tests using N,N-dicyclohexylmethylamine in ethanol with cesium pivalate, the system produced dicyclohexylamine in an 89 percent yield over 16 hours. Control experiments showed that the reaction does not proceed in the absence of light, oxygen, base, or photocatalyst. Copper-free carbon nitride yielded only 30 percent of the product, confirming the role of the dispersed copper centers.
Reaction scope and scalability
The catalytic method tolerated a wide selection of cyclic and acyclic aliphatic amines, aromatic amines, and heterocyclic compounds, delivering secondary amines in yields ranging from 40 to 89 percent. The protocol also successfully modified complex pharmaceutical molecules, including the alkaloid (-)-lobeline, the antidepressant imipramine hydrochloride, and a stanolone steroid derivative. In a 10-millimole scale-up experiment, the reaction produced 1.65 grams of product in a 71 percent yield. The catalyst retained its operational activity over more than ten consecutive reuse cycles.
Catalyst structure and synthesis
Spectroscopic characterization confirmed the atomic dispersion of copper across the support. X-ray absorption near-edge structure measurements placed the copper in a partial positive oxidation state between +1 and +2. Extended X-ray absorption fine structure spectra showed a primary coordination shell of copper-nitrogen and copper-oxygen bonds at approximately 1.5 angstroms, with no metallic copper-copper scattering peak near 2.2 angstroms.
Preparation of the catalyst involves combining dicyandiamide, 2-amino-5-(trifluoromethyl)benzonitrile, and copper nitrate trihydrate in water, followed by drying and calcining at 550 degrees Celsius for four hours. The finished material possesses an electronic band gap of 2.65 electronvolts and a valence band potential of +1.39 volts, which prevents over-oxidation of secondary amine products.
