Synthesis of Palladium and Platinum Complexes with Phosphine-Functionalized Benzimidazolin-2-ylidene Ligands

Phosphine-functionalized benzimidazolium salts of the type N -(2-phosphinoethyl)- N ‘-alkylbenzimidazolium chloride ( 4, alkyl = ethyl; 5, alkyl = n -propyl; 6, alkyl = n -butyl) and N, N ‘-bis(2-phosphinoethyl)-5,6-dimethylbenzimidazolium chloride ( 9 ) have been prepared. The reaction of 4 − 6 with silver oxide followed by a carbene transfer reaction from silver to palladium or platinum gave complexes of the type cis -[M(PC NHC )Cl 2 ] 13 − 18 (M = Pd, Pt; PC NHC = N -(2-phosphinoethyl)- N ‘-alkylbenzimidazolin-2-ylidene). The pincer-type complexes [M(PC NHC P)Cl]Cl (M = Pd ( 20 ), Pt ( 21 ); PC NHC P = N, N ‘-bis(2-phosphinoethyl)benzimidazolin-2-ylidene) with a diphosphine-functionalized carbene ligand have been synthesized by carbene transfer from the corresponding silver complex [Ag(PC NHC P)Cl] ( 19 ) to [PdCl 2 (cod)] or [PtCl 2 (PhCN) 2 ]. The metathesis reaction of 20 with silver tetrafluoroborate in pyridine produced [Pd(PC NHC P)py](BF 4 ) 2 ( 22 ). Compounds 13, 15, and 22 ·0.5MeOH have been characterized by X-ray diffraction. Heck-type coupling reactions of several aryl halides with styrene and n -butyl acrylate have been studied with the palladium complexes containing phosphine-functionalized carbene ligands as catalysts.