Synthesis and Characterization of N‑Trifluoromethyl N‑Heterocyclic Carbene Ligands and Their Complexes

Starting from N-trifluoromethyl
benzimidazole
(1), a series of N-trifluoromethyl benzimidazolium
salts 2a–f·HA 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 N-trifluoromethyl NHC ligands was investigated in π-acidic
Au­(I)-catalyzed hydroalkoxylation of cyclohexene. The gold complexes
bearing NHCs 2a and 2c–e compete with [Au­(PPh3)­Cl] in terms of catalytic activity.

以N-三氟甲基苯并咪唑(1)为起始原料，一系列N-三氟甲基苯并咪唑盐2a-f·HA已被成功制备并进行了全面表征。这些盐类参与了[Ir(CO)2(NHC)-Cl]、[Rh(COD)(NHC)-Cl]、[Se(NHC)]和[Au(NHC)-Cl]衍生物的合成。对[Air(CO)2(NHC)-Cl]复合物的红外光谱分析表明，氮原子上的三氟甲基取代基显著降低了碳烯碳的σ供电子能力。相反，这些新型配体的π受体性质得到增强。对[Se(NHC)]加合物77Se核磁共振共振和[Rh(NHC)(COD)Cl]复合物的氧化还原电势的研究进一步证实了这一假设。此外，这些新型的N-三氟甲基NHC配体的效率在π酸性Au(I)-催化的环己烯烷氧基化反应中得到了考察。携带NHCs 2a和2c-e的贵金属复合物在催化活性方面可与[Au(PPh3)Cl]相媲美。