Diarylformamides as a Safe Reservoir and Room Temperature Source of Ultra-Pure CO in the Context of a 'Green' rWGS Reaction

Diphenylformamide 1 and bisformamide 9 are shown to be safe reservoirs and sources of CO. Their perfectly selective decarbonylations are achieved in solution at room temperature with potassium and cesium diarylamide catalysts. 1 is obtained in excellent yields directly from triethylammonium formate, which may be the product of CO₂ scrubbing with NEt₃ and catalytic hydrogenation. 1 thus represents a key intermediate in a low-temperature rWGS reaction sequence. Moreover, solvent-free decarbonylations of 1 may be run either in the melt at 70 °C or with 9 even in the solid state at 88 °C with improved atom economy. These simple and practical transition-metal-free decarbonylations afford ultra-pure (i. e. dry and solvent-free) CO at moderate temperatures and the diarylamines byproducts are recycled as pure compounds. In the absence of catalysts, diarylformamides 1 and 9 are long-term stable at >200 °C. DFT-calculations indicate a reaction pathway with a rate-determining deprotonation of Ph₂NC(O)H and barrier-free CO elimination from Ph₂NC(O)^-.