Tailoring metal complexes with N-heterocyclic carbene ligands using Electron-Withdrawing Groups: Impact on catalytic activity and property development

In the field of catalytic chemistry, metal complexes containing N-heterocyclic carbenes (NHCs) have gained significant attention due to their versatile nature and wide range of potential applications. In the synthetic applications, the catalytic properties of M/NHC complexes are affected by the incorporation of sterically hindered donor substituents into NHC ligands. However, a comparative analysis of M/NHC complexes with electron-acceptor substituents revealed significant differences in catalytic activity and selectivity. The complexes exhibit enhanced performance in several catalytic transformations. Therefore, this review focuses on substituents with electron-acceptor properties to explore their impact on the catalytic efficiency, stability and general characteristics of the resulting M/NHC complexes. Additionally, the potential for their use in catalytic processes is examined. Both experimental and computational methodologies have been employed to shed light on this phenomenon, revealing that electron-withdrawing groups play a significant role in altering the electronic properties of the molecule and creating unique spatial environments around the metal center. This, in turn, greatly influences the reactivity, stability and selectivity of M/NHC catalysts. The findings analyzed in this review elucidate the critical contribution of electron-withdrawing substituents in the design and optimization of efficient M/NHC catalysts. This opens up new avenues for innovation in the development of novel catalysts and applications in the ever-evolving field of catalysis.