Synthesis of New Dipyrido-Annulated N‑Heterocyclic Carbenes with Ortho Substituents

A method for the introduction of
various substituents at the 4 and 8 positions of 2,10-di-tert-butyldipyrido­[1,2-c;2′,1′-e]­imidazolium salts, is described. The new imidazolium salts
bearing substituents (R′ = Cl, SPh) at the 4 and 8 positions
are synthesized in three-step procedures, and carbenes generated from
the imidazolium salts can be used to give the corresponding rhodium
complexes. The role of the 4,8-substituents can be either bystanders
or coordinating ligands according to the nature of the metal moiety.