Coordination Versatility of NHC-metal Topologies in Asymmetric Catalysis: Synthetic Insights and Recent Trends

Asymmetric metal based catalysis has advanced quickly in recent years, with its efficiency relying exclusively on chiral ligands. Rational design and meticulous selection of chiral ligands have led to many breakthroughs in the recent decades. In the realm of asymmetry, N-heterocyclic carbene ligands (NHCs) are one of the most widely deployed chiral architectures. Both steric and electronic aspects facilitate the unexpected chemical stability and coordination adaptability of many NHCs with a wide range of transition metals. Further, the facile synthesis of precursors and ease way to introduction of chiral elements into NHCs backbone, has made NHCs potential ligands in metal-based asymmetric catalysis. As a result, the number of strategies for designing efficient NHC–metal catalysts for novel asymmetric chemical transformations has skyrocketed. This review article provides an in depth and up-to-date review on NHC-metal based asymmetric catalysis that spans the years 2015 to 2021. Also addressed the main synthetic approaches for making this broad class of compounds, as well as the importance of structural fine tuning of NHC ligands in boosting ee in challenging chemical transformations that can spur progressions in this field.