Metal‐Metal Interactions in Bi‐, Tri‐ and Multinuclear Fe, Ru and Os N‐Heterocyclic Carbene Complexes and their Catalytic Applications

Abstract

AbstractN‐heterocyclic carbenes (NHCs) have been the focal point of advanced research on catalysis and bioorganometallic chemistry in the last decade. The field of NHC‐metal mediated catalysis has steadily grown over past years, commencing from the seminal discoveries on various C−C, C−N coupling and acceleration of C−H bond activation reactions. This review presents an overview of the work about the effects of NHC ligand field on metal‐metal contacts in Fe, Ru and Os metal NHC complexes. The influence of these contacts in making the supramolecular assemblies and their consequences on the reactivity patterns is reviewed. Correspondingly, the synergic effects between two metals leading to a unique reactivity pattern are correlated. The suitability and efficiency of various synthetic protocols used to prepare bi‐, tri‐ and multinuclear transition metal NHC complexes where metal‐metal contacts are possible, is discussed. Alternatively, this study on metal‐metal contacts in Fe, Ru and Os metal NHC complexes has great potential in the fields of homogeneous and heterogonous catalysis including the new designs for efficient hydrogen evolution electrocatalysts and oxidation and acylation catalysts. Rational ligand design leading to metal‐metal contacts by the appropriate functionalization of NHCs to investigate their applications in mentioned fields are thus fundamental to our efforts. Apart from their applications, the nature of the metal‐carbene carbon bond, nature of auxiliary ligand(s) and the influence of suitably functionalized NHC ligands led to generate advanced structural motifs have also been emphasized.