Palladium-catalyzed sequential Heck/Suzuki coupling reaction and the synthesis of diarylmethanes in aqueous media using indole-based N-heterocyclic carbene precursors

Abstract

This study introduced a versatile class of indole-based benzimidazolium salts, offering distinct advantages: (1) the utilization of affordable and easily accessible starting materials; (2) a straightforward and uncomplicated synthesis process; (3) the diversity of the salt should provide fine-tunability of steric and electronic properties. These salts, employed as N-heterocyclic carbene (NHC) precursors, were effectively utilized in the Pd-catalyzed C–C bond formation reactions involving aryl or benzyl halide. The catalytic system, arising from the in situ generation of Pd(OAc)₂ and indole-based benzimidazolium salts, demonstrated remarkable efficiency. It accomplished the synthesis of diarylmethanes via the Suzuki coupling of benzyl chlorides and arylboronic acids in aqueous media with a Pd loading of 0.5 mol%. Furthermore, it successfully achieved the one-pot sequential Heck/Suzuki coupling reactions with a Pd loading of as low as 0.25 mol%.