Phosphonium salt as an aryl donor in coupling reactions

Abstract

Use of quaternary phosphonium salts as an aryl donor has been investigated in the Pd-catalyzed olefination and cross-coupling reactions with regard to substrate scope and mechanistic aspects. It turned out that palladium(0) adds oxidatively into aryl-phosphorous bond of phosphonium salts leading to (Ar3P)2PdArX adducts which were readily detected and characterized by ESI-MS and X-ray crystallography, respectively. We have shown that coupling reactions of phosphonium salts with olefins, boron compounds, and terminal alkynes are efficiently carried out by the use of palladium catalysts under suitable conditions to afford the coupled products in good to excellent yields. It was also revealed that aryl-aryl exchange in the intermediates (Ar3P)2PdArX proceeds rapidly under catalytic conditions, and, as a result, aryl transfer from differently substituted tetraarylphosphonium salts is non-selective in Pd-catalyzed cross coupling reactions.