Catalytic Palladium Phosphination: Modular Synthesis of C1-Symmetric Biaryl-Based Diphosphines
Résumé
A new family of C1-symmetric bis(diphenylphosphino)biphenyls have been prepared starting from readily available ortho,ortho′-dihalobiphenyl precursors by a palladium-catalyzed C–P coupling reaction. This process does not require the use of an additional ligand. To date, the synthesis of such diphosphines, by reaction of an intermediate biphenyldiyl dianion with ClPPh2, mainly afforded the undesired cyclic phosphafluorene derivative. So far, no synthetic pathway has been found to avoid this intramolecular reaction. Herein we report the first general and external-ligand-free palladium-catalyzed phosphination reaction that allows the synthesis of a wide variety of substituted ortho,ortho′-bis(diphenylphosphino)biphenyls. With the aim of illustrating the scope and efficiency of this methodology, we applied it to the establishment of a straightforward access to C1-symmetrical analogues of the most powerful ligands used in homogenous catalysis and extended it to more challenging substrates.