Recent advances in transition-metal-catalyzed N-formylation of amines with sustainable C1 sources.

Formamides are indispensable intermediates in the synthesis of pharmaceuticals, agrochemicals, and functional materials. Yet, their conventional preparation relies on toxic stoichiometric reagents, including acetic formic anhydride, formyl chloride, and chloral, resulting in poor atom economy and substantial waste generation. Transition-metal catalysis has emerged as a sustainable alternative, enabling direct N-formylation of amines using renewable C1 feedstocks under mild conditions. This review summarizes advances reported from 2019 to 2026, covering six major C1 sources: carbon dioxide, methanol, biomass-derived carbonyl compounds (glycolic acid, glycerol derivatives, and oxalic acid), formic acid, paraformaldehyde, and triethyl orthoformate. Recent homogeneous manganese-, iron-, and copper-based systems for CO2 utilization, together with heterogeneous cobalt-based metal-organic frameworks and Co(II)-embedded covalent organic framework photocatalysts, demonstrate the expanding scope of catalytic N-formylation. This review critically evaluates mechanistic pathways involving carbamate and formamide intermediates, cobalt-formate species, silyl formates, oxidative C-C bond cleavage, and radical processes. By comparing catalyst architectures, C1-source characteristics, reaction conditions, mechanistic features, and sustainability considerations, this review identifies key structure-activity and selectivity trends and highlights emerging opportunities for the rational development of efficient, selective, recyclable, and sustainable N-formylation methodologies.