Palladium-Catalyzed Suzuki−Miyaura Cross-Coupling Reactions Employing Dialkylbiaryl Phosphine Ligands

The cores of many types of polymers, ligands, natural products, and pharmaceuticals contain biaryl or substituted aromatic structures, and efficient methods of synthesizing these structures are crucial to the work of a broad spectrum of organic chemists. Recently, Pd-catalyzed carbon-carbon bond-forming processes, particularly the Suzuki-Miyaura cross-coupling reaction (SMC), have risen in popularity for this purpose. The SMC has many advantages over other methods for constructing these moieties, including mild conditions, high tolerance toward functional groups, the commercial availability and stability of its reagents, and the ease of handling and separating byproducts from its reaction mixtures. Until 1998, most catalysts for the SMC employed triarylphosphine ligands. More recently, new bulky and electron-rich phosphine ligands, which can dramatically improve the efficiency and selectivity of such cross-coupling reactions, have been introduced. In the course of our studies on carbon-nitrogen bond-forming reactions, we found that the use of electron-rich and bulky phosphines enhanced the rate of both the oxidative addition and reductive elimination processes; this was the beginning of our development of a new family of ligands, the dialkylbiarylphosphines L1-L12. These ligands can be used for a wide variety of palladium-catalyzed carbon-carbon, carbon-nitrogen, and carbon-oxygen bond-forming processes as well as serving as supporting ligands for a number of other reactions. The enhanced reactivity of these catalysts has expanded the scope of cross-coupling partners that can be employed in the SMC. With use of such dialkylbiarylphosphine ligands, the coupling of unactivated aryl chlorides, aryl tosylates, heteroaryl systems, and very hindered substrate combinations have become routine. The utility of these ligands has been successfully demonstrated in a wide number of synthetic applications, including industrially relevant processes. In this Account, we provide an overview of the use and impact of dialkylbiarylphosphine ligands in the SMC. We discuss our studies on the mechanistic framework of the reaction, which have allowed us to rationally modify the ligand structures in order to tune their properties. We also describe selected applications in the synthesis of natural products and new materials to illustrate the utility of these dialkylbiarylphosphine ligands in various "real-world" synthetic applications.