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

Abstract

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 CD3CN solutions with rates k = 3.30 ± 0.04 × 10−4 s−1 (Ar = Ph, 1a[NEt4]) and k = 1.96 ± 0.01 × 10−4 s−1 (Ar = C6H4OMe-4, 1b[NEt4]) at 0 °C. Reactions of the zwitterion with Me2NCHS and pyridine gave the corresponding products [closo-B12H11-1-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.