Polydentate P, N-based ligands for palladium-catalyzed cross-coupling reactions

Abstract

In recent years, Pd-catalyzed cross-coupling reactions have been used widely as expeditious reactions in various fields of chemistry. Traditionally, these cross-coupling reactions have been carried out by using different phosphine ligands. Though the phosphine ligands have been extensively used, they suffer from many limitations like poor air, moisture, and thermal stability. Hence, in recent years phosphine-free ligands such as N-heterocyclic carbenes and amines have attracted countless attention in the field of catalysis. Unfortunately, the ligands having only N as a donor atom can activate aryl iodides and bromides, while aryl chlorides are less reactive. Hence, the P–N ligands containing functional moiety, with donor N or P atom have been prepared and used for different organic transformations. An even more effective mixed donor P, N-ligands have many advantages in asymmetric catalysis because of the distinctly different characteristics like a ‘soft’ P-ligand as a π-acceptor and a ‘hard’ N-ligand as a σ-donor. This compressive review highlights the results of the highly active ligands and complexes containing N in combination with P as a donor atom.