title: New catalysts with unsymmetrical N-heterocyclic carbene ligands.
abstract: The importance of unsymmetrical N-heterocyclic carbenes (uNHCs) as ligands in metal-catalyzed reactions is undeniable. While uNHCs show similar properties as compared with symmetrical NHCs, dissymmetrization allows for further fine-tuning. The introduction of chelatization, hemilability, bifunctionality, shielding effects, and chirality-transfer influences the catalyst's stability, reactivity, and selectivity, thus offering access to tailor-made systems including mono- and multidentate uNHC ligands. Based on selected examples, the structure-reactivity relationship of uNHCs employed in metal catalysts is presented. The focus is on catalytically active complexes, which either offer access to new applications or lead to significantly improved results in metal-catalyzed reactions.
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Strasse des 17 Juni 135, D-10623 Berlin, Germany.
authors.forename: Johanna
authors.initials: J
authors.lastname: Tornatzky
authors.forename: Axel
authors.initials: A
authors.lastname: Kannenberg
authors.forename: Siegfried
authors.initials: S
authors.lastname: Blechert