Pyrazole and (pyrazol-1-yl)metal complexes as carbon–carbon coupling catalysts

Pyrazolyl ligands have been used to prepare metal complexes since the mid-1960s as nitrogen-donor ligands. However, unlike other nitrogen-donor ligands like imines and pyridines, their metal complexes have not been used extensively in catalysis. This review highlights the emergence of pyrazolyl metal complexes as nitrogen-donor catalysts, particularly in carbon–carbon coupling reactions. The focus is on olefin oligomerization and polymerization, acetylene oligomerization and polymerization, Heck and Suzuki coupling and ring opening polymerization of cyclic monomers. It highlights successes and problems of these catalysts, but draws attention to this burgeoning area so that other researchers can take advantage of these remarkable ligands.