investigation of catalytic activity and kinetics of a pd/biphenyl-based phosphine system in the ullmann cross-coupling of para-substituted aryl bromides

Catalytic activity of a pd/biphenyl based- phosphine system in the ullmann cross-coupling reaction of various para-substituted aryl bromides were investigated. the results showed that the bulky electron-rich phosphine efficiently modify the electronic and steric properties of palladium center and promote the cross-coupling reaction. mechanistic study using the hammett correlation revels that electron-withdrawing substituents decrease the electron density at the palladium center and decrease the rate of oxidative-addition step such that this step will become the rate determining step (rds). on the other hand, electron-donating groups increase the rate of oxidativeaddition step such that the reductive-elimination step will become the rds.