title: Carboranes as Aryl Mimetics in Catalysis: A Highly Active Zwitterionic NHC-Precatalyst.
abstract: Modern catalysis takes advantage of aryl-based interactions to tune and control reactions. In the design of N-heterocyclic-carbene catalysts, both the electronic and steric nature of the nitrogen substituents play a crucial role. Although hydrocarbon-based systems and especially aryl residues have contributed considerably to overcome multifaceted catalytic challenges, the unique properties of carborane moieties, including delocalized charge, potential planar chirality, and well-known thermodynamic stability, offer unprecedented opportunities to develop new catalysts while being employed as aryl mimetics. We report a straightforward synthetic route to a novel zwitterionic triazolium-based N-heterocyclic carbene (NHC) precatalyst bearing a 7,8-dicarba-nido-undecaboranyl substituent. The catalyst's excellent activity and its broad applicability are demonstrated in a wide range of organocatalytic transformations. Comparison of the performance with known N-aryl NHC catalysts offers preliminary insights into the stereoelectronic nature of this nido-carboranyl substituent.
authors.affiliation: Institut für Organische Chemie, Universität Leipzig, Johannisallee 29, 04103, Leipzig, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Selg
authors.affiliation: Institut für Anorganische Chemie, Universität Leipzig, Johannisallee 29, 04103, Leipzig, Germany.|Current address: Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, 02139, USA.
authors.forename: Wilma
authors.initials: W
authors.lastname: Neumann
authors.affiliation: Institut für Anorganische Chemie, Universität Leipzig, Johannisallee 29, 04103, Leipzig, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Lönnecke
authors.affiliation: Institut für Anorganische Chemie, Universität Leipzig, Johannisallee 29, 04103, Leipzig, Germany.
authors.forename: Evamarie
authors.identifier: http://orcid.org/0000-0003-4267-0603
authors.initials: E
authors.lastname: Hey-Hawkins
authors.affiliation: Institut für Organische Chemie, Universität Leipzig, Johannisallee 29, 04103, Leipzig, Germany.
authors.forename: Kirsten
authors.identifier: http://orcid.org/0000-0003-1549-5002
authors.initials: K
authors.lastname: Zeitler
keywords: N-heterocyclic carbenes; carboranes; heterocycles; organocatalysis; zwitterions