Synthesis and Characterization of <i>N</i>‑Trifluoromethyl N‑Heterocyclic Carbene Ligands and Their Complexes

Starting from <i>N</i>-trifluoromethyl benzimidazole (<b>1</b>), a series of <i>N</i>-trifluoromethyl benzimidazolium salts <b>2a</b>–<b>f·HA</b> have been prepared and fully characterized. These were engaged in the formation of [Ir­(CO)₂(NHC)­Cl], [Rh­(COD)­(NHC)­Cl], [Se­(NHC)], and [Au­(NHC)­Cl] derivatives. IR analysis of [Ir­(CO)₂(NHC)­Cl] complexes revealed that the trifluoromethyl substituent on nitrogen significantly decreases the σ-donating ability of the carbene carbon. On the other hand, the π-acceptor property of these novel ligands is enhanced. Examination of the ⁷⁷Se NMR resonance of [Se­(NHC)] adducts and the redox potentials of [Rh­(NHC)­(COD)­Cl] complexes further supports this assumption. In addition, the efficiency of these new <i>N</i>-trifluoromethyl NHC ligands was investigated in π-acidic Au­(I)-catalyzed hydroalkoxylation of cyclohexene. The gold complexes bearing NHCs <b>2a</b> and <b>2c</b>–<b>e</b> compete with [Au­(PPh₃)­Cl] in terms of catalytic activity.