Cyclic (Aryl)(Amido)Carbenes: NHCs with Triplet-like Reactivity.

Authors :: Sultane PR
Ahumada G
Janssen-Müller D
Bielawski CW
Source :: Angewandte Chemie (International ed. in English) [Angew Chem Int Ed Engl] 2019 Nov 04; Vol. 58 (45), pp. 16320-16325. Date of Electronic Publication: 2019 Sep 24.
Publication Year :: 2019
Abstract: The synthesis and study of a library of cyclic (aryl)(amido)carbenes (CArAmCs), which represent a class of electrophilic NHCs that feature low calculated singlet-triplet gaps (ΔE <subscript>ST</subscript> =19.9 kcal mol <superscript>-1</superscript> ; B3LYP/def2-TZVP) and exhibit reactivity profiles expected from triplet carbenes, are described. The electrophilic properties of the CArAmCs were quantified by analyzing their respective selenium adducts, which exhibited the largest downfield <superscript>77</superscript> Se NMR chemical shifts (up to 1645 ppm) measured for any NHC derivative known to date, as well as their Ir carbonyl complexes, from which large Tolman electronic parameter (TEP) values (up to 2064 cm <superscript>-1</superscript> ) were ascertained. The CArAmCs were found to engage in reactions that are typically observed with triplet carbenes, including C-H insertions, [2+1] cycloadditions with alkenes as well as alkynes, and spontaneous oxidation upon exposure to oxygen.<br /> (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)