Enabling room-temperature reductive C-N coupling of nitroarenes: combining homogeneous and heterogeneous synergetic catalyses mediated by light

The green synthesis of (hetero)aromatic amines is highly expected but challenging. Here, we demonstrate a promising protocol for the room-temperature reductive C-N coupling of nitroarenes mediated by direct light without any catalyst, avoiding harsh reaction conditions of all involving reported homogeneous and heterogeneous thermal catalyses. In addition, the promotive photothermal synergistically catalytic reductive C-N coupling of nitroarenes was further proven by combining 365 nm of UV light with heterogeneous plasmonic MoO3 nanosheets. The catalytic tests reveal that the light-mediated reaction process closely correlates with the applied light wavelength. Impressively, exfoliated MoO3 affords better photoresponsive efficiency, promotive photoelectron transfer, and plasmonic photothermal conversion effect, thus improving the thermal reactivity by photothermal synergy in contrast to bulky MoO3. More importantly, we further reveal the coupling efficiency of the reaction with a greener ethanol solution compared to that using an optimal toluene solvent by light combined with MoO3 nanosheets. The light-mediated reductive coupling reaction mechanism and superiority were further validated by DFT calculations and control experiments. The present protocol demonstrates broad substrate scopes, high functional-group tolerance, excellent chemoselectivity, and great practical applicability.

Automated summary

In this study, a light-mediated reductive C-N coupling method for nitroaromatic compounds without the use of a catalyst and harsh reaction conditions is demonstrated. The effectiveness of photothermal synergy catalysis was further validated.