Sustainable Catalyst-free N-formylation using CO₂ as a Carbon Source

The development of new sustainable catalytic conversion methods of carbon dioxide (CO₂) is of great interest in the synthesis of valuable chemicals. N-formylation of CO₂ with amine nucleophiles as substrates has been studied in depth. The key to benign formylation is to select a suitable reducing agent to activate CO₂. This paper showcases the activation modes of CO₂ and the construction strategies of sustainable and catalyst-free N-formylation systems. The research progress of catalyst-free N-formylation of amines and CO₂ is reviewed. There are two broad prominent categories, namely reductive amidation of CO₂ facilitated by organic solvents and ionic liquids in the presence of hydrosilane. Attention is also paid to discussing the involved reaction mechanism with practical applications and identifying the remaining challenges in this field.