Ag(I) and Pd(II) complexes of a 1,3-dibenzhydryl substituted benzannulated N-heterocyclic carbene: Unexpected rearrangement, structures and catalytic studies

Reaction of the sterically bulky 1,3-dibenzhydrylbenzimidazolium bromide (Bh2-bimyH+Br−) (A) with Pd(OAc)2 in DMSO yielded a mono(carbene) Pd(II) complex 1 with a N-bound benzimidazole derivative, which resulted from an unusual NHC rearrangement reaction. Reaction of A with Ag2O, on the other hand, cleanly gave the Ag(I) carbene complex [AgBr(Bh2-bimy)] (2), which has been used as a carbene-transfer agent to prepare the acetonitrile complex trans-[PdBr2(CH3CN)(Bh2-bimy)] (3). Dissociation of acetonitrile from complex 3 and subsequent dimerization afforded the dinuclear Pd(II) complex [PdBr2(Bh2-bimy)]2 (4) in quantitative yield. All complexes were fully characterized by multinuclear NMR spectroscopies, ESI mass spectrometry and X-ray diffraction analysis. Furthermore, the catalytic activity of complex 4 in aqueous Suzuki–Miyaura cross-coupling reactions was studied and compared with that of its previously reported less bulky analogue [PdBr2(iPr2-bimy)]2.

Graphical abstractA series of Ag(I) and Pd(II) complexes with the bulky 1,3-dibenzhydrylbenzimidazolin-2-ylidene ligand has been synthesized. One of these complexes contains an unusual benzimidazole ligand, which resulted from a complex rearrangement reaction. The catalytic activity of a dimeric Pd(II) complex in the Suzuki–Miyaura reaction is also described.Figure optionsDownload full-size imageDownload as PowerPoint slide