Synthesis of pincer-type bis(benzimidazolin-2-ylidene) palladium complexes and their application in C-C coupling reactions

Reaction of the xylene-bridged bisbenzimidazolium salts 2,6-bis(N-alkyl-N'-methylenebenzimidazolium)-1-bromophenylene dibromide (1, alkyl = ethyl; 2, alkyl = n-propyl; 3, alkyl = n-butyl) with [Pd-2(dba)(3)] yields the palladium pincer complexes of type [Pd(L)Br], 4-6 (L = 2,6-bis(N-alkyl-N'-methylenebenzimidazolin-2-ylidene)phenylene). Pincer complexes 4-6 have been tested as precatalysts in Heck and Suzuki coupling reactions of various aryl bromides with styrene and phenylboronic acid, respectively.