An Imidazolium Salt That Uncharacteristically Avoids the Imminent Deprotonation of Its Acidic 2‑H Proton by KN(SiMe3)2

KN(SiMe3)2, a non-nucleophilic strong base, rarely misses deprotonating an imidazolium-2-H to give its N-heterocyclic carbene (NHC). We report a rare case of a -CH2-linked bifunctional imidazolium-phenol [HO-4,6-tBu2-C6H2-2-CH2{CH(NCHCHNAr)}]Br [LH2Br; Ar = 2,6-iPr2–C6H3 (Dipp)], whose attempted double deprotonation by KN(SiMe3)2 majorly gives an unusual substitution product [(DippImd)K{O-4,6-tBu2-C6H2-2-CH2N(SiMe3)2}] (1; DippImd = CH{(NCHCHN(Dipp)}). Apparently, the second KN(SiMe3)2, instead of deprotonating the imidazolium-2-H, substitutes the whole imidazolium moiety from the benzylic carbon. Control experiments indicate a SN1-type mechanism. But the intermediate LH, seemingly a zwitterionic imidazolium aryloxide, also shows a steady self-fragmentation by releasing free DippImd to suggest a complex formative route for 1. Interestingly, LiN(SiMe3)2 in contrast favors the expected double deprotonation but further undergoes a 1,2-benzyl migration to give trimeric [Li(O-4,6-tBu2-C6H2-2-CH2{C(NCHCHNAr)}]3 [4]3. Two plausible routes for the substitution and deprotonation are proposed using DFT calculations. However, considering the complexities involved, a better clarity of the Li/K divergence would require a more accurate modeling of the reaction species and explicit solvent molecules.