Phosphine mono- and bis-ylide palladacycles as homogeneous molecular precatalysts: Simple and efficient protocol greatly facilitate Suzuki and Heck coupling reactions

Abstract

Moisture/air-stable and robust phosphine mono- and bis-ylide palladacycles as catalyst precursors were used in Suzuki and Heck cross-coupling reactions with different aryl halides including electron-rich and electron-deficient substituents. These coupling reactions could proceed smoothly in air under optimized reaction conditions (Suzuki coupling: 0.001mol% of palladacycle, Cs2CO3 in DMF at 110°C; Heck coupling: 0.001mol% of palladacycle, K2CO3 in NMP at 130°C), affording the corresponding products in mostly good to excellent yields. Filtration experiments and poisoning studies indicate that the phosphine-ylide palladacycles decompose under reaction conditions to form active Pd (0) homogeneous species. These homogenous catalysts were exhibited high catalytic activities in the presence of low catalyst loadings, providing high yields of desired products. Applications of five-member palladacycle [(P^C)PdCl2] (1) in these coupling reactions produced comparable catalytic activities of seven-member analogs [(C^C)PdCl2] (2). We found that the palladacycle complexes containing bulky, symmetrical and unsymmetrical phosphorus ylides are the active catalysts in the appropriate Suzuki and Heck cross-coupling reactions.