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(PCNHC)Cl2] 13−18 (M = Pd, Pt; PCNHC = N-(2-phosphinoethyl)-N‘-alkylbenzimidazolin-2-ylidene).
The pincer-type complexes [M(PCNHCP)Cl]Cl (M = Pd (20), Pt (21); PCNHCP = 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(PCNHCP)Cl] (19) to [PdCl2(cod)] or [PtCl2(PhCN)2]. The metathesis reaction of 20 with silver tetrafluoroborate in pyridine produced [Pd(PCNHCP)py](BF4)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.