A Simple Zinc Catalyst for Carbamate Synthesis Directly from CO₂

Several zinc salts were employed as catalysts for the synthesis of carbamates directly from aromatic amines, CO₂ , and silicate esters. Zn(OAc)₂ offered the best performance among the salts tested. The addition of an N-donor ligand such as 1,10-phenanthroline increased the yield. The best catalytic performance of Zn(OAc)₂ can be explained by carboxylate-assisted proton activation. The interaction between the substrate and the catalyst can be observed by chemical shifts in ¹ H and ¹⁵ N NMR spectra. Isocyanate was a key intermediate, which was generated from amine and CO₂ . Silicate ester was finally converted to siloxane, which was determined by ²⁹ Si NMR. The commercially available catalyst system could be reused. The yield of isolated carbamate could reach up to 96 % with various substrates, and the catalytic reaction was amine-selective in the presence of other functional groups.