NCN pincer six-membered NHC palladium complexes were synthesized, characterized and used in Heck reaction of aryl bromides with olefines.

A series of asymmetrical substituted tetrahydropyrimidinium salts and different kinds of bridged bistetrahydropyrimidinium salts were prepared through the quaterization of tetrahydropyrimidine or the dehydrogenation of hexahydropyrimidine. They were characterized and used as NHC precursors in the palladium catalyzed Buchwald-Hartwig amination reaction. The in situ formed catalytic system Pd(OAc) 2 /tetrahydropyrimidinium and t BuOK catalyzed the amination of heteroaryl halides and heterocyclic amines effectively, producing the heterocyclic amine functionalized heteroaryl derivatives in high yields.

Two newly synthesized pincer palladium complexes are shown to be efficient catalysts for the Heck reaction of aryl bromides with acrylates or styrene.

In the title methyl­ene-bridged di(tetra­hydro­pyrimidinium) salt, C33H50N4 2+·2Br−·C2H5OH·H2O, the two tetra­hydro­pyrimidinium rings have envelope conformations with the central CH2 C atom as the flap. Their mean planes are inclined to one another by 73.31 (13)° and the attached benzene rings are inclined to one another by 67.39 (15)°. The methylene-C—N bond lengths in the tetra­hydro­pyrimidinium rings are 1.314 (3) and 1.304 (3) Å, values typical for C=N double bonds. The distances between the methyl­ene-bridge C atom and the linked tetra­hydro­pyrimidinium N atom are 1.457 (3) and 1.465 (3) Å, values typical for C—N single bonds. The mol­ecules co-crystallized with H2O and EtOH mol­ecules from the solvent. In the crystal, there is a zigzag chain along [010] of water mol­ecules linked by one of the Br− anions via O—H⋯Br hydrogen bonds. The second Br− anion is hydrogen bonded (O—H⋯Br) to the ethanol solvent mol­ecule. There are also a number of C—H⋯Br and C—H⋯O hydrogen bonds present, leading to the formation of a two-dimensional network lying parallel to the bc plane.