Toward elemental gold leaching: Synthesis of Au–NHC complexes from a masked NHC precursor

• The masked carbenes have been used to transfer the NHC ligands to metal salts. • 1,3-Dimethylimidazolium-2-carboxylate react with metallic gold to generate Au-NHC. • There is great interest in environmentally friendly extraction of precious metals. 1,3-Dimethylimidazolium-2-carboxylate is a convenient precursor for the in situ generation of N -heterocyclic carbene 1,3-dimethylimidazolylidene ( Me NHC) in aprotic solvents and aerobic atmosphere. The Me NHC carbene readily reacts with [Au(tht)Cl], [Au(PPh 3 )Cl], and K[AuCl 4 ], which are common starting compounds in gold organometallic chemistry, to generate [Au( Me NHC)Cl], [Au( Me NHC) 2 ] + , and [Au( Me NHC) 2 Cl 2 ] + complexes, respectively. Interestingly, 1,3-dimethylimidazolium-2-carboxylate can react with metallic gold powder in the presence of CuI to generate [Au( Me NHC) 2 ] + cation. This methodology avoids the use of aggressive oxidizing agents, toxic chelating agents, or strongly acid or basic media commonly used in gold leaching processes. This reaction suggests the potential for developing more environmentally friendly methods for gold extraction in the future.