Phosphine Oxide-Promoted Rh(I)-Catalyzed C-H Cyclization of Benzimidazoles with Alkenes.

Ligands play a critical role in promoting transition-metal-catalyzed C-H activation reactions. However, owing to high sensitivity of the reactivity of C-H activation to metal catalysts, the development of effective ligands has been a formidable challenge in the field. Rh(I)-catalyzed C-H cyclization of benzimidazoles with alkenes has been faced with low reactivity, often requiring very harsh conditions. To address this challenge, a phosphine oxide-enabled Rh(I)-Al bimetallic catalyst was developed for the reaction, significantly promoting the reactivity and allowing the reaction to run at 120 °C with up to 97% yield.