Wanzlick's equilibrium in tri- and tetraaminoolefins. Issue 23 (26th October 2021)

• Record Type: Journal Article
• Authors: Messelberger, Julian; Kumar, Manoj; Goodner, Stephen J.; Munz, Dominik
• Is Part Of: Organic chemistry frontiers. Volume 8:Issue 23(2021)
• Page Start: 6663
• Page End: 6669
• Publication Date: 2021-10-26
• Subjects: Chemistry, Organic -- Periodicals; 547.005
• DOI: 10.1039/d1qo01320c
• Languages: English
• ISSNs: 2052-4110

Abstract

Abstract : How to isolate small carbenes, previously reported to from dimers instantaneously, and how to split triaminoolefins into free carbenes. Abstract : The dissociation mechanism of electron-rich olefins into their parent carbenes has been a controversial topic since Wanzlick's pioneering work. Herein, we present a combined synthetic and computational study on the formation (dissociation, respectively) of hetero- and homo-carbene dimers derived from benzimidazolin-2-ylidenes (benzNHCs), imidazolidin-2-ylidenes (saNHC), and cyclic (alkyl) (amino) carbenes (CAACs) through sublimation ( in vacuo ) as well as in condensed phase. We quantify the effect of proton catalysis and report that even triaminoolefins dissociate to their free carbenes, yet only under proton catalysis. Accordingly, we report how the judicious choice of the base (KO t Bu vs. KHMDS) and solvent (hexane/benzene vs. THF) allows N, N ′-dimethylbenzimidazolin-2-ylidene to be obtained quantitatively as a metastable, kinetic product. This free carbene had been previously reported to dimerize directly to the olefin-dimer, which is the thermodynamic product.