Xantphos-ligated Palladium Dialkyl Complex as an EffectivePrecatalyst for Cross-coupling Reactions

摘要

Palladium-catalyzed cross-coupling reactions have become one of the most powerfulmethods for the formation of C-C and C-heteroatom bonds.1 The development of palladiumprecatalysts,which generate catalytically active and coordinatively unsaturated paradium(0) species,is an important subject for efficient cross-coupling reactions.2 AlthoughXantphos has been employed in a variety of palladium-catalyzed C-C and C-heteroatombond forming reactions,Buchwald and co-workers have reported that the catalyticallyinactive bis-ligated palladium species Pd(Xantphos)2 can be readily formed during thesereactions.3 Highly active palladacyclic precatalysts bearing a variety of phosphine ligandswere developed to solve this problem by Buchwald and co-workers.4 However,theseprecatalysts form carbazole-based byproducts upon catalyst activation,which couldpotentially lead to subsequent catalyst inhibition and complicate the purification step.