Formamides are widely used in industry as solvents and raw materials for synthesis. The use of CO₂ as a C1 building block has been industrialized mainly in the production of urea. Therefore, the development of efficient methods to convert urea derivatives to formamides can be useful for CO₂ utilization. However, urea derivatives can be difficult to hydrogenate. In addition, the hydrogenation of formamides is generally easier than that of the urea derivatives, which makes it difficult to avoid over-hydrogenation.

Haoran Li, Zhejiang University, Hangzhou, China, and colleagues have developed a ruthenium-catalyzed semi-hydrogenation of urea derivatives that can be used to prepare formamides with high selectivity. The team used (PPh₃)₃RuCl₂ as a catalyst precursor, 1,1,1-tris(diphenylphosphinomethyl)ethane as a ligand, KO^tBu as an additive, and tetrahydrofuran (THF) as the solvent. The reactions were performed at 140 °C under 50 bar H₂.

 

 

Under these conditions, various alkyl and aryl urea derivatives were successfully hydrogenated to obtain the corresponding recyclable amines and the desired formamides (up to 97 % yield). A Ru(II) dihydride complex (pictured above) was confirmed to be the catalytically active species. The team discovered that even at much lower H₂ pressures (< 5 bar), the conversion efficiency was not affected, but the selectivity was reduced. Since the employed alkyl and aryl urea derivatives are easily obtained by a reaction of CO₂ and amines, their hydrogenation provides an environmentally friendly pathway for the indirect conversion of CO₂ to formamides.

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• Highly Efficient Ruthenium‐Catalyzed Semihydrogenation of Urea Derivatives to Formamides,
  Jun Zhu, Yue Zhang, Zeyu Wen, Qiyi Ma, Yongtao Wang, Jia Yao, Haoran Li,
  Chem. Eur. J. 2023.
  https://doi.org/10.1002/chem.202300106