The Fluoride Method: Access to Silver(III) NHC Complexes

We have synthesized the first silver(III) carbene complexes, (CF₃ )₃ Ag(NHC), by direct reaction of the silver(III) fluoride precursor complex [PPh₄ ][(CF₃ )₃ AgF] with different imidazolium salts. This novel methodology circumvents the use of free NHC molecules. The silver(III) carbene complexes thus prepared are unprecedented and show remarkable thermal stabilities. They display square-planar or square-pyramidal geometry. Following our calculations, the electronic structure of a model representative complex exhibits Inverse Ligand Field (ILF). The compounds reported herein are synthetic analogues of the elusive difluorocarbene and carbonyl species proposed as intermediates in the acidic decomposition of [Ag(CF₃ )₄ ]^- . The synthetic procedure reported is envisaged to enable access to carbene complexes of other late transition-metals in high oxidation states.