Ring‐Expanded N‐Heterocyclic Carbenes for Copper‐Mediated Azide–Alkyne Click Cycloaddition Reactions

A series of well‐defined copper(I) complexes bearing ring‐expanded N‐heterocyclic carbene (NHC) ligands has been applied to the azide–alkyne cycloaddition reaction. The obtained results notably showed that the six‐membered NHC ligands outperform well‐established five‐membered ones. [CuI(Mes‐6)] displayed a remarkable catalytic activity while respecting the strict criteria for click reactions. May the best win: The screening of different pre‐formed [CuX(NHC)] complexes (NHC=N‐heterocyclic carbene) showed that in the formation of [1,2,3]‐triazoles, the activity was in the order NHC‐6>NHC‐5≫NHC‐7. Overall, [CuI(Mes‐6)] displayed a remarkable catalytic activity while respecting the strict criteria for click reactions.