New Addition To P,N Family Of Ligands

By constructing a triazole ring as a substituent on a phosphole ring, Yoshihiro Matano and coworkers of Kyoto University, in Japan, have created a new type of P,N chelating ligand (Org. Lett., DOI: 10.1021/ol901194m). The synergistic heterocyclic groups make the phosphole-triazole hybrid optimal for coordinating metals to make catalysts or to make supramolecular materials with useful optical properties. Matano's group recently reported the synthesis of a silyl-capped ethynylphosphole, which they recognized as a potential candidate for the copper-mediated Huisgen cycloaddition reaction that is a primary way to make triazoles by welding an aryl azide to an ethynyl group. In the new report, the team describes a multistep reaction using the new phosphole and the Huisgen method to make the first known examples of triazole-substituted phospholes. When testing the ability of the hybrids as P,N ligands, the researchers found that palladium coordinates in the anticipated P,N chelate fashion. But when it comes to platinum, a dimer complex forms in which the metal binds only to the phosphorus atoms of two ligands. In addition, palladium chelation significantly alters the electronic properties of the ligand's conjugated π system, providing a means to modulate optical properties.