Well-defined Zn-complexes in homogeneous catalysis: recent advances and future scope.

Zinc is the second most abundant trace element and it is involved in many biological functions. Its ability to bind with organic molecules enables it to act as a key metal ion in various enzymes such as carbonic anhydrase, carboxypeptidase A, alcohol dehydrogenase, and alkaline phosphatase. Zinc participates in different physicochemical reactions under biological conditions. However, the application of zinc as a catalyst in synthetic chemical transformations is limited. Simple zinc salts are usually used as Lewis acid catalysts in chemical reactions. However, well-defined zinc complexes with specific ligands have been less studied. Recent studies have shown that well-designed ligands can lead to efficient zinc catalysts, expanding their role beyond that of a traditional Lewis acid and allowing for more selective and versatile chemical transformations. This review sheds light on well-defined zinc complexes with different organic ligands used in various homogeneous catalytic reactions, such as borylation, silylation, dehydrogenation, hydrogenation, hydroamination, CO2 insertion, etc. Being a redox inactive metal centre, a zinc catalyst usually works through sigma bond metathesis and insertion steps. This review also covers recent studies on zinc-catalyzed multielectron catalysis involving organic radicals. Lastly, the possibility of zinc-catalyzed asymmetric reactions with properly designed zinc complexes bearing chiral ligands is summarized.