Alkylation of Aromatic Amines with Trialkyl Amines Catalyzed by a Defined Iridium Complex with a 2-Hydroxypyridylmethylene Fragment

Abstract

Six Cp*Ir complexes containing NN-bitentate chelate ligands [Cp*IrCl(C5H4CH2C5H3OH)][Cl] (1), [Cp*IrCl(C5H4CH2C5H3O)] (2), [Cp*IrCl(C5H4C5H3OH)] [Cl] (3), [Cp*IrCl(C5H4CH2C5H4)][Cl] (4), [Cp*IrCl(CH3OC5H3CH2C5H3OCH3)][Cl] (5), and [Cp*IrCl(CH3OC5H3CH2C5H3OH)][Cl] (6) were synthesized and characterized. Complex 1 could be transformed to 2 when reacted with NaOtBu or NEt3 via −OH deprotonation. These six complexes were tested as catalysts for mono-N-alkylation of amines with trialkyl amines, and complex 1 exhibited highest activity. The coupling reactions proceed under air condition, with 1 mol % catalyst loading without extra base in methanol at 120 °C and can be further accelerated by adding NR3·HCl.