New Ligands Beyond N-Heterocyclic Carbenes for Application in Homogeneous Catalysis.

Building on the success of N-heterocyclic carbenes, extended versions comprised of an exocyclic metal bonding site have become increasingly popular. Pyridinium amidates (PYAs) belong to these ligand systems, as they contain a N-donor site that is formally stabilized by a pyridine-derived carbene. These PYAs are characterized by a unique donor flexibility, which imparts in some settings extraordinarily high catalytic activity, and in other settings remarkable stability of (catalytic) intermediates, which allows for deciphering mechanistic pathways.