4-Sulfanylmethyl- and 4-sulfonylmethyl-substituted N,N′-diarylimidazolium salts as new proligands in the synthesis of Pd complexes with N-heterocyclic carbenes

The reaction of readily available N,N′-diaryl-4-chloromethylimidazolium chlorides with thiols afforded 4-(alkyl)arylsulfanylmethyl-N,N′-diarylimidazolium salts. The oxidation of these salts with hydrogen peroxide catalyzed by ammonium paramolybdate gave the previously unknown 4-(alkyl)arylsulfonylmethyl-N,N′-diarylimidazolium salts. The synthesized imidazolium salts can be used as sources of N-heterocyclic carbenes (NHCs). The conditions were found for the selective palladation of these compounds involving the C(2) atom of the imidazole ring. Palladium complexes with NHC ligands functionalized with RSCH₂ and RSO₂CH₂ groups were synthesized. The potential applicability of these complexes as catalysts for cross-coupling reactions was demonstrated.