A series of substituted 12‐sulfonium zwitterions 1[n] and one example of a 1‐sulfonium analogue 2[5]a were prepared in four steps. Derivatives 1[n] exhibit rich crystalline polymorphism and a high‐temperature SmBcry phase stabilized by dipolar interactions. Solution studies in a nematic host demonstrated positive dielectric anisotropy of compounds 1[5]a–1[5]c (Δε ≈ +18 extrapolated from 8 mol‐% solutions) resulting from a longitudinal electric dipole moment of ca. 9.5 D. The effectiveness of additives 1[5] was analyzed by using the Maier–Meier formalism and DFT methods and compared to those of more polar derivatives 3[6]a and Pyr[10].

Diazotization of [closo-1-CB11H10-1-R-12-NH2](-)[NMe4](+) (4[NMe4]) in neat 4-methoxypyridine leads to 12-(4-methoxypyridinium) zwitterions [closo-1-CB11H10-1-R-12-(4-MeOC5H4N)] (2) in ∼50% yield. Demethylation of 2 with LiCl in dimethylformamide provides access to 12-pyridones 5[NMe4], which can be O-alkylated with alkyl triflates giving 12-(4-alkoxypyridinium) zwitterions, such as 1. This three-step process is more efficient than direct diazotization of amine 4[NMe4] in neat higher 4-alkoxypyridine. The new method was demonstrated for the synthesis of [closo-1-CB11H10-1-C5H11-12-(4-C7H15OC5H4N)] (1c), which exhibits a smectic A phase. Molecular and electronic structures of 4-methoxypyridinium zwitterion 2b and its C(1) isomer [closo-1-CB11H11-1-(4-MeOC5H4N)] (3b) were investigated by single-crystal X-ray diffraction and spectroscopic methods, respectively, and the experimental results were compared to those obtained with density functional theory methods. Lastly, the mechanism for formation of zwitterions 2 was investigated computationally revealing low energy for dediazoniation of the [closo-1-CB11H10-1-R-12-N2] (14) intermediate (ΔG298 ≈ 25 kcal/mol) to form boronium ylide 15, with weak dependence on substituent R. Dinitrogen derivative 14c was observed by (11)B NMR spectroscopy.

Pyridinium zwitterions ofcloso-boranes were conveniently obtained from 4-alkoxypyrylium salts and investigated as high Δεadditives to nematics.