Palladium-Catalyzed Coupling Reaction By The C-P Bond Cleavage Of Phosphonium Salt

Phosphine ligands play a vital role in stabilizing active metal center atoms and fine-tuning the selectivity of reactions in transition metal-catalyzed reactions.However,studies in recent years found that C-P bonds of phosphine ligands were cleaved in transition metal-catalyzed reactions which aroused the interest of the researchers.A series of explorations and studies have been performed on this cleavage and activation of the C-P bond.Based on these research background,our research focused on the palladium-catalyzed coupling reactions which realized by the C-P bond cleavage of phosphonium salt combined with different nucleophiles.The main contents include the following two aspects:1.A series of biphenyl derivatives were synthesized successfully which used quaternary phosphonium salt and arylboronic acid as the reaction substrate,Pd?CH₃CN?₂Cl₂ as the catalyst for the reaction.In the transformation,the C-P bond in the quaternary phosphonium salt was broken to form a carbon-palladium active intermediate which followed by the Suzuki coupling with arylboronic acid to afford the target product.This reaction was similar to the traditional Suzuki coupling but in this reaction,the formation of the carbon-palladium bond is through the rupture of the C-P bond of the quaternary phosphonium salt rather than the oxidative addition of aryl halide.This reaction had good functional group tolerance.All arylboronic acids bearing electron-withdrawing groups or electron-donating groups proceeded smoothly to afford corresponding products in moderate to excellent yields.2.A series of olefin derivatives were synthesized using Cu O as oxidant,Pd?OAc?₂ as catalyst,and quaternary phosphonium salt and olefin as substrates.The reaction is similar to the traditional Heck reaction.The difference was that the quaternary phosphonium salt instead of the aryl halide acted as the electrophile reagent in the reaction.The investigation of the generality of this transformation showed that the reaction has good functional group compatibility.The above two works all used quaternary phosphonium salt as electrophilic reagent.Under palladium catalysis,the C-P bond in the quaternary phosphonium salt was broken to form active carbon-palladium intermediate which then reacted with different nucleophile reagents to generate corresponding targets products.These research results provided a new research idea for the cleavage and transformation of the C-P bond.