Palladium-N-heterocyclic carbene complexes for the Mizoroki-Heck reaction: An appraisal

This article presents a review of the most significant developments with N-heterocyclic carbene (NHC)-palladium catalytic systems used for the Heck reaction. For more than the past two decades, a large number of new NHC-Pd complexes have been synthesized and characterized. These studies focused on NHCs as a phosphine analogue, but the current review highlights the differences with particular ligands so as to attain a suitable balance between the electronic and bulky environments around the metal. NHCs have gained wide recognition as these ligands act as excellent σ-donors that form stable metal-NHCs with strong metal-carbon bonds. For this reason, metal-NHCs are commonly used as they are highly reactive and can selectively serve as catalysts for various chemical transformations. The objective of our article is to highlight significant recent progress in NHC-Pd(II) complexes and provide an overview of their extensive interaction in the Mizoroki-Heck reaction.