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 S_N1-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.