24: Enabling Catalytic Applications of Aminocarbene Ligands through Rational Design

The rational design of transition-metal catalysts is one of the appealing contemporary areas of chemical research, driven by sustainability and waste reduction targets. In this context, many distinct types of ancillary ligands were evaluated as supporting ligands in transition-metal catalysis with heteroatom-stabilized carbenes, i.e., N-heterocyclic (NHCs) and acyclic diaminocarbenes (ADCs), dominating the field. Tuning of the electron-donor capacity and steric properties of aminocarbenes, essential for the success of their catalytic applications, has been mainly achieved via the empirical variation of their structures. In this context, complexes with NHCs are typically assembled through the direct coordination of the carbene species to a metal center, whereas the complexes with ADCs are generally obtained via an alternative route based on metal-mediated nucleophilic addition to isocyanides. The latter approach is atom-efficient and high-yielding, allowing for an easy variation of the periphery of aminocarbenes through the careful selection of a suitable isocyanide–nucleophile pair ensuring high synthetic flexibility. Insofar as the structure of an aminocarbene species is concerned, several key structural points associated with the emergence of catalytic properties are recognized, including the nature of the metal center, steric and electronic properties as well as the binding mode of the aminocarbene ligands, the presence of secondary ancillary ligands and the manifestation of non-covalent interactions in the metal complex structure. In this survey, we reflect on the application of representative metal–ADC complexes in catalysis, focusing on the recognition of the structural features of the carbene complexes leading to the manifestation of their catalytic properties.