[PdCl2{8-(di-tert-butylphosphinooxy)quinoline)}]: a highly efficient catalyst for Suzuki–Miyaura reaction

The complex [PdCl2(P–N)] containing the basic and sterically demanding 8-(di-tert-butylphosphinooxy)quinoline ligand (P–N) is a highly efficient catalyst for the coupling of phenylboronic acid with aryl bromides or aryl chlorides. The influence of solvent and base has been investigated, the highest rates being observed at 110 °C in toluene with K2CO3 as the base. With aryl bromides the reaction rates are almost independent on the electronic properties of the para aryl substituents, on the contrary, reduced reaction rates are observed when bulky substituents are present on the substrate. Nevertheless the coupling of 2-bromo-1,3,5-trimethylbenzene with phenylboronic acid can be carried out to completion in 2 h using a catalyst loading of 0.02 mol %. Under optimized reaction conditions, turnover frequencies as high as 1900 h−1 can be obtained in the coupling of 4-chloroacetophenone with phenylboronic acid; lower reaction rates are obtained with substrates bearing EDG substituents on the aryl group.