Effect of Electron-Deficient Phosphenium Ligands on the Pd(II)-Catalyzed Electrophilic Carboxylation Reaction of Substituted Benzenes

摘要

Carboxylation of substituted benzenes using formic acid as a carbonyl source has been achieved when an electrophilic palladium(II) complex was employed as a catalyst under acidic condition.An addition of phosphenium cation as an additive to the electrophilic palladium(II) catalyst system led to improvement of reaction yields and suppression of hydroxylated byproducts.Screening of the phosphenium cations revealed that p-methoxyphenyl substituted derivative gave the best yield.Under the reaction temperature of 30 deg C,the largest amount of carboxylated benzenes were obtained.The scope of present Carboxylation by the use of phosphenium cation covered a wide range of mono- and di- substituted benzenes,even trisubstituted benzene.The phosphenium cation may have played a role as an activator towards formic acid and/or as a ligand.