The terphenyl phosphine TXPhos: A highly efficient and general supporting ligand for palladium-catalyzed C-N cross-coupling of aryl chlorides with diaryl amines as well

Abstract

An efficient C-N cross-coupling between readily available aryl chlorides and diaryl amines has been established by using Pd/TXPhos as catalyst, leading to a diversity of triarylamines in high yields. Detailed experimentation revealed that terphenyl phosphine ligand TXPhos exhibited premier catalytic performance in comparison with common ligands and the choice of base and solvent was crucial to reactivity. Strong bases, such as NaOtBu and LHMDS, were the preferred ones for electron-rich diarylamines, while bases including alkali metal carbonates and phosphates were the suitable choice for diarylamines possessing electron-withdrawing substituents. Notably, the use of TXPhos as supporting ligand enabled the extension to weak base such as NaOPh with electron-rich diarylamine substrates. Mechanistic studies indicated that a Pd phenolate species initially formed after the oxidative addition step when NaOPh was employed as the base, which would facilitate the generation of Pd-amide complex after amine coordination. The synthetic utility of this coupling protocol was exemplified by the efficient synthesis of several carbazole-based OLED molecules and the practicality was demonstrated by the achievement of up to 3300 TON.