Fine Tuning of Dirhodium(II) Complexes: Exploring the Axial Modification

Over the years, dirhodium(II) complexes have had an important role in the synthesis of numerous complex organic molecules because many useful transformations are mediated by this unique family of complexes. The recognized success of this class of catalysts relies on their bimetallic structure. They have a Rh–Rh bond, two axial ligands, and four bridging ligands responsible for controlling the catalyst electrophilicity and, in some cases, provide a mechanism for inducing asymmetry. The modification of the bridge ligand structure has been the main strategy to prepare new complexes, whereas the axial ligands have been considered to have a less important role in catalysis. This concept is changing, and over the past decade, the axial ligand modification was proven to be a valuable and simple strategy to prepare new complexes and achieve new reactivities. In this review a comprehensive overview of this topic is presented, with a particular focus on the changes induced by the axial coordination on the complex properties and reactivity.