Traditional ligands well proven in the field of coordination chemistry include amines, phosphines and carboxylates. Nevertheless, recent years are characterized by a revolutionary change in the field of non-traditional ligands such as carbenes, nitrenes, borylenes, and ambiphilic species possessing novel electronic and steric properties and are challenging traditional paradigms in the field of coordination chemistry. In this review, we discuss the emerging frontier of these unconventional ligands, within the settings of small molecule activation, as well as homogeneous catalysis. Non-traditional ligands open up the boundary of catalysis by allowing mild conditions to activate inert molecules including H2, N2, CO2, and CH4 in a wide variety of bond breaking/making reactions. It focuses on the design of ligands, metal-ligand cooperativity and how these ligands mechanistically promote multi-electron transformations. The combination of spectroscopic, computational and structural data also illuminate the effect such new ligand frameworks have on reactivity, selectivity and stability. The review shows the recent breakthroughs and upcoming scope of exploiting non-conventional ligands in sustainable catalysis with particular focus on sustainable chemical transformations, energy conversion and fine chemical synthesis.
Ahmed et al. (Sat,) studied this question.