Synthesis and Catalytic Activity of Pincer-Type Bis(benzimidazolin-2-ylidene) Palladium Complexes

Abstract

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.