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.

Saturated N‐Heterocyclic Carbene Based Thiele's Hydrocarbon with a Tetrafluorophenylene Linker

“…[6g] Recently,w eh ave studied the reactivity of C 6 F 6 and C 6 F 5 CF 3 with SIPr. [8] In this work, we show the utilization of CÀFbond activation of C 6 F 6 chemistry to realize a SIPr-based Thiele's hydrocarbon spanned by aC 6 F 4 linker.T he question remains whether the four substituted fluorinea toms at the central phenylene ring of 3 would destabilize the quinoid state and stabilize the biradical state. Af urther impetusc omes from the works of Abe and co-workers who showedt he increase in the biradical character in 1,4-bis-(4,5-diphenylimidazol-2-ylidene) tetrafluoro cyclohexa-2,5-diene (tf-BDPI-2Y) from parent BDPI-2Y.…”

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

“…Molecular structure (ORTEP) of 6. [37] Anisotropic displacement parametersa re depicted at the 50 %p robability level. Hydrogen atoms (except at N2 atom) are not shown for clarity.Incrystal packing one Fatom of BF 4 À shows disorder and occupied in two different sites with 40 %a nd 60 %o ccupancy.S elected bond lengths []a nd angles [8 8]: C1-N1 1.327(3), C1-N2 1.322(3), C1-C4 1.504(4), C2-C3 1.314(4), F3-B1 1.312 (5);N 1-C1-N2 122.3(2), C2-N1-C1 121.8(2), N1-C1-C4 118.1(2), F3-B1-F2 98.2(3).…”

“…Molecular structure (ORTEP) of 2 with anisotropic displacement parametersd rawn at 50 %probability level. [37] Hydrogen atoms (except in the SIPr backbone) are not shown for clarity.S elected bond lengths []and angles [8 8]: C1-N1 1.320(4), C1-N2 1.334(4), C2-N1 1.472 (5)…”

“…Molecular structure (ORTEP) of 3 with anisotropic displacement parametersd rawn at 50 %probability level [37]. Hydrogen atoms (except HF 2 À )a re not shown for clarity.S elected bond lengths []and angles [8 8]: C5-N2 1.3137(18), C5-N1 1.3152(18), N2-C18 1.4844(18), N1-C19 1.4874(18), C18-C19 1.544(2), C5-H5 0.9300, F1-H30 1.233-(18);N1-C5-N2 112.91(13), C19-C18-N2 102.57(11), C18-N2-C5 111.06(12).…”

“…Molecular structure (ORTEP) of 5 [37]. Anisotropic displacement parametersa re depicted at the 50 %p robability level.…”