Nitrenium Ion Chemistry

Alla Pogoreltsev, Schulich Faculty of Chemistry, Technion – Israel Institute of Technology, Haifa, Israel
Heroot Levy, Schulich Faculty of Chemistry, Technion – Israel Institute of Technology, Haifa, Israel
Mark Gandelman, Schulich Faculty of Chemistry, Technion – Israel Institute of Technology, Haifa, Israel

N-heterocyclic nitrenium ions are the nitrogen-derived cationic analogues of N-heterocyclic carbenes. Unlike N-heterocyclic carbenes and their analogues, the binding of these species to transition metals remained elusive for a long time.  Recently, our group reported the preparation of several N-heterocyclic nitrenium ions and demonstrated, for the first time, coordination of these species to various transition metal centers (such as Rh, Ru and Pt).^[i]

Here we present the mono- and di-cationic Ir(I) complexes coordinated to the N-heterocyclic nitrenium cations. The formation of dicationic Ir(I) complexes is particularly interesting, since the coordination of a cationic ligand to a cationic metal is an extremely rare. Moreover, such unexplored complexes can lead to a novel unusual reactivity, since this cation-cation (L⁺-M⁺) system enhances the electrophilicity of the metal center. The binding of nitrenium ligand to metal center exhibits it Lewis basic (σ-donor and π-acid) character.

Here we also present, for the first time, the function of nitrenium species as Lewis acid. Nitrenium ions react with various basic species affording new type of Lewis acid-base pairs.^[ii] In light of chemistry of frustrated Lewis pairs and Lewis acid-base pairs based on carbenes and their analogue, we hope that these new pairs will expand the field of metal-free activation of small molecules. 

The formation of the nitrenium-metal or nitrenium-nucleophile bond is confirmed in solution by selective ¹⁵N-labelling experiments, and/or in the solid state by X-ray crystallography.

^[i] a) Tulchinsky, Y.; Iron, M. A.; Botoshansky, M.; Gandelman, M. Nature Chem. 2011, 3, 525. (b) Tulchinsky, Y.; Kozuch, S.; Saha, P.; Botoshansky, M.; Shimon, L.; Gandelman, M. Chem. Sci. 2014, 5, 1305.    

^[ii] Unpublished results.