C−F Bond Activation by a Saturated N‐Heterocyclic Carbene: Mesoionic Compound Formation and Adduct Formation with B(C₆F₅)₃

Abstract

The reaction of SIPr, [1,3‐bis(2,6‐diisopropylphenyl)‐imidazolin‐2‐ylidene] (1), with C6F6 led to the formation of an unprecedented mesoionic compound (2). The formation of 2 is made accessible by deprotonation of the SIPr backbone with simultaneous elimination of HF. The C−F bond para to the imidazolium ring in 2 is only of 1.258(4) Å, which is the one of the shortest structurally authenticated C−F bonds known to date. The liberation of HF during the reaction is unequivocally proved by the addition of one more equivalent of SIPr, which leads to the imidazolium salt with the HF2− anion. To functionalize 2, the latter reacted with B(C6F5)3 to give an unusual donor–acceptor compound, where the fluoride atom from the C6F5 moiety coordinates to B(C6F5)3 and the carbanion moiety remains unaffected. Such coordination susceptibility of the fluoride atom of a nonmetallic system to a main‐group Lewis acid (Fnon‐metal→BR3) is quite unprecedented.

Activation of C–F, Si–F, and S–F Bonds by N-Heterocyclic Carbenes and Their Isoelectronic Analogues

“…A related mesoionic product was obtained by Sen and co-workers when a saturated NHC 10 was used as a nucleophile (Scheme 11, bottom). 58,59 In this case, the NHC backbone underwent deprotonation under reaction conditions. In the presence of BF 3 and 2 equivalents of 10, double substitution occurred.…”

Photoinduced Dual C−F Bond Activation of Hexafluorobenzene Mediated by Boron Atom

“…The common approach to activate C−F bonds thus far relies on low‐valent, low‐coordinate transition‐metal complexes by an oxidative addition [6] . Nevertheless, some main‐group species are highly reactive and mimic the reactivity of transition‐metal complexes as well, for instance, strong Lewis acids, frustrated Lewis pairs (FLPs), [7,8] N‐heterocyclic carbene (NHC), [8] two‐coordinate divalent Group 14 compounds, [9] base stabilized silylenes and germylenes, [10] N‐heterocyclic aluminylenes, [11] Mg I ‐Mg I bonded compounds [12] and the N‐heterocyclic olefin (NHO) 1,3,4,5‐tetramethyl‐2‐methyleneimidazoline, [13] to name just a few. Very recently, Wu and co‐workers have reported a site‐selective C−F activation of polyfluoroarenes via electrophotocatalysis [14] .…”