Observing C–N bond formation in plasma: a case study of benzene and dinitrogen coupling via an arylnitrenium ion intermediate

Abstract

Directly fixing dinitrogen into value-added organics is one of the core issues, and yet a long-standing challenge, in chemical synthesis. In earlier discrete studies, direct amination of benzene with N₂ has been achieved via non-thermal plasma-liquid reaction. Nonetheless, the reaction mechanism thereof remains elusive and the amination product was non-selective primarily including aniline and diphenylamine. Herein, non-thermal plasma reaction in combination with on-line mass spectrometry was employed to probe the reaction pathway by on-line detection of the transient intermediate and the stable amination product. The long-lived atomic nitrogen ions N⁺(³P) as well as the arylnitrenium ions’ intermediacy were shown to play a pivotal role in the amination process, and the product distribution was affected by an external hydrogen source and likely dependent on the competing hydrogen abstraction reaction and intersystem crossing of the initially generated triplet state arylnitrenium ions. The mechanistic investigation in this work has implications for plasma-based nitrogen conversion into organics, but also has broader relevance for understanding the C–N coupling by other means directly with N₂.