Synthesis and catalytic activity of pincer-type bis(benzimidazolin-2-ylidene) palladium complexes

Reaction of the bridged bisbenzimidazolium salts 2,6-bis(N-1-alkyl-N-3-methylenebenzimidazolium)pyridine dibromide (1, alkyl = methyl; 2, alkyl = ethyl; 3, alkyl = n-propyl; 4, alkyl = n-butyl) with palladium acetate yields the palladium pincer complexes of type [Pd(L)Br]Br, 5-8 (L = 2,6-bis(N-1-alkyl-N-3-methylenebenzimidazolin-2-ylidene)pyridine). Compounds 1, 2(.)0.5MeOH, 4(.)CH(2)Cl(2), and 6(.)MeOH (L = 2,6-bis(N-1-ethyl-N-3-methylenebenzimidazolin-2-ylidene)pyridine) were characterized by X-ray diffraction. The molecular structure of 6 shows a distorted square-planar coordination geometry for the palladium atom. In situ generated pincer complexes 5-8 have been tested as catalysts in Heck-type coupling reactions of different aryl halides with styrene.