The [closo-B12H11-1-IAr]- zwitterion as a precursor to monosubstituted derivatives of [closo-B12H12]2-

Reactions of [closo-B12H12](2-) with ArI(OAc)(2) in aqueous AcOH in the presence of [NEt4](+) or [NHEt3](+) give [closo-B12H11-1-IAr](-) (1) in 74-95% yield as a white precipitate. The zwitterions decompose in CD3CH solutions with rates k = 3.30 +/- 0.04 x 10(-4) s(-1) (Ar = Ph, 1a[NEt4]) and k = 1.96 +/- 0.01 x 10(-4) s(-1) (Ar = C6H4OMe-4, 1b[NEt4]) at 0 degrees C. Reactions of the zwitterion with Me2NCHS and pyridine gave the corresponding products [closo-R12H11-1-SCHNMe2](-) (2) and [closo-B12H11-1-NC5H5](-) (3) isolated in 25 -27% and up to 44% yield, respectively. The former anion is a protected thiol derivative, which was transformed to the sulfonium derivative [closo-B12H11-1-S(CH2)(5)](-) (8). The molecular structure and spectroscopic properties of pyridinium zwitterion 3 were analyzed experimentally and computationally (B3LYP), and results compared with those for the [closo-B10H9-1-NC5H5](-) (4) analog. Mechanisms of formation of 2-4 from appropriate aryliodonium zwitterions were analyzed with the M062x computational method. (C) 2015 Elsevier B.V. All rights reserved.