Catalysts for Suzuki−Miyaura Coupling Processes: Scope and Studies of the Effect of Ligand Structure
Suzuki?Miyaura coupling reactions of aryl and heteroaryl halides with aryl-, heteroaryl- and vinylboronic acids proceed in very good to excellent yield with the use of 2-(2?,6?-dimethoxybiphenyl)dicyclohexylphosphine, SPhos (1). This ligand confers unprecedented activity for these processes, allowing reactions to be performed at low catalyst levels, to prepare extremely hindered biaryls and to be carried out, in general, for reactions of aryl chlorides at room temperature. Additionally, structural studies of various 1·Pd complexes are presented along with computational data that help elucidate the efficacy that 1 imparts on Suzuki?Miyaura coupling processes. Moreover, a comparison of the reactions with 1 and with 2-(2?,4?,6?-triisopropylbiphenyl)diphenylphosphine (2) is presented that is informative in determining the relative importance of ligand bulk and electron-donating ability in the high activity of catalysts derived from ligands of this type. Further, when the aryl bromide becomes too hindered, an interesting C?H bond functionalization-cross-coupling sequence intervenes to provide product in high yield.