[Pd(Phbz)(X)(PPh3)] palladacycles promote the base-free homocoupling of arylboronic acids in air at room temperature

摘要

Homocoupling of arylboronic acids can be successfully achieved in commercial grade THF using [Pd(Phbz)(X)(PPh3)] palladacycles as catalysts (Phbz = N-phenylbenzaldimine; X = imidate or acetate). Symmetric biaryls were obtained in good yields working under mild conditions in an air atmosphere at room temperature. The reaction occurs without the addition of an exogenous base. The reaction conditions were optimized to provide the homocoupled products in excellent yield. Evidence for the transmetallation step being important for precatalyst activation has been gathered. The influence of electronic properties of the arylboronic acids on the outcome of the homocoupling reaction has been assessed through competition experiments.