Development of New Phosphine Ligands (BRIDPs) for Efficient Palladium-Catalyzed Coupling Reactions and Their Application to Industrial Processes

A new series of phosphine ligands, the 2,2-diphenylvinylphosphines (vBRIDPs) 1 and 2,2-diphenylcyclopropylphosphines (cBRIDPs) 2, were designed and synthesized. Despite their high electron density on phosphorus, BRIDPs are air stable because of their unique structures that prevent their oxidation to the phosphine oxides. A catalyst system consisting of BRIDPs and palladium species effectively catalyzes coupling reactions of a wide range of aryl halides with arylboronic acids, amines, and aryl ketones. In this article, typical preliminary examples of coupling reactions, such as the Suzuki-Miyaura coupling and the Buchwald-Hartwig amination, are described along with two concepts of ligand design, which are based on the electron richness and steric hindrance of vBRIDPs 1a and 1b and their structural hybrids, cBRIDPs 2a and 2b. In addition, we also compare the characteristics of Pd/BRIDP complexes with different substituent groups on the phosphorus atom, such as tert-butyl and cyclohexyl groups, and give some examples of successful applications of these ligands to industrial processes.