| Summary: | In recent years, several classes of new <i>N</i>-heterocyclic carbene (NHC) ligands were developed around the concept of “flexible steric bulk”. The steric hindrance of these ligands brings stability to the active species, while ligand flexibility still allows for the approach of the substrate. In this review, the synthesis of several types of new classes, such as <b>IBiox</b>, cyclic alkyl amino carbenes (<b>CAAC</b>), <b>ITent</b>, and <b>IPr*</b> are discussed, as well as how they move the state-of-the-art in palladium catalyzed cross-coupling forward.
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