Photocatalytic Formamide Synthesis via Coupling of Electrophilic and Nucleophilic Radicals over Atomically Dispersed...

Formamide (HCONH₂) plays a pivotal role in the manufacture of a diverse array of chemicals, fertilizers, and pharmaceuticals. Photocatalysis holds great promise for green fabrication of carbon-nitrogen (C-N) compounds owing to its environmental friendliness and mild redox capability. However, the selective formation of the C-N bond presents a significant challenge in the photocatalytic synthesis of C-N compounds. This work developed a photocatalytic radical coupling method for the formamide synthesis from co-oxidation of ammonia (NH₃) and methanol (CH₃OH). An exceptional formamide yield rate of 5.47±0.03 mmol ⋅ g_cat ^-1 ⋅ h^-1 (911.87±5 mmol ⋅ g_Bi ^-1 ⋅ h^-1) was achieved over atomically dispersed Bi sites (Bi_SAs) on TiO₂. An accumulation of 45.68 mmol ⋅ g_cat ^-1 (2.0 g ⋅ g_cat ^-1) of formamide was achieved after long-term illumination, representing the highest level of photocatalytic C-N compounds synthesis. The critical C-N coupling for formamide formation originated from the "σ-σ" interaction between electrophilic ⋅CH₂OH with nucleophilic ⋅NH₂ radical. The Bi_SAs sites facilitated the electron transfer between reactants and photocatalysts and enhanced the nucleophilic attack of ⋅NH₂ radical on the ⋅CH₂OH radical, thereby advancing the selective C-N bond formation. This work deepens the understanding of the C-N coupling mechanism and offers an intriguing photocatalytic approach for the efficient and sustainable production of C-N compounds.