To Anlyse the Ag2o Technique Has Been the Most Popular Method In the Synthesis of Ag (I)–Nhcs |
The present work revealed that the Ag2O technique has beenthe most popular method in the synthesis of Ag(I)–NHCs and in their subsequentuses as transmetallating agents. The Ag2O technique is tolerant of activatedhydrogen atoms adjacent to functional groups. The use of normal azolium halideled to the formation of ionic or neutral Ag(I)–NHCs in the solidstate,depending on factors such as counter-ions, carbene cores, N-substituents andthe crystallization conditions. A fluxional behavior between the ionic andneutral complexes was observed in solution for most of the compounds. The ionicor neutral compounds displayed structural diversity to give monomeric, dimericand polymeric forms depending on the steric bulkiness around the Ag(I)–NHCs. Insome instances non-stoichiometric X−/AgX2− were reported; this happened becausethe AgX2− was in equilibrium with AgX(s) and X−. This problem can be resolvedif the halide ion was replaced by non-coordinating anions. Depending on the nature of the imidazolium salts, thesynthetic reactions conducted with excess Ag2O yielded interesting products.For example, the reaction of long N-alkyl chain containing imidazolium orbenzimidazolium salts with excess Ag2O produced stable AgNPs in solution alongwith the AgNHCs. When N-pyridyl functionalized imidazolium salts reacted withexcess Ag2O, the triangulo-[Ag3(_-NHC)3]+3 complexes (Scheme 17a and b) withbridging _2-carbenes and unusual Ag· · ·Ag interactions were generated.