Synthesis of oxonium derivatives of the dodecahydro-closo-dodecaborate anion [B12H12]2−. Tetramethylene oxonium derivative of [B12H12]2− as a convenient precursor for the synthesis of functional compounds for boron neutron capture therapy

Synthesis of novel derivatives of closo‐dodecaborate anion with azido group at the terminal position of the spacer

“…The 11 B NMR pattern of compound 4 (unlike compound 3) in CDCl 3 does depend on the concentration of the solution. Thus, for example, while only one signal (δ B 6.5) was observed in the low-field region for the 0.12 M solution of 4 (giving the spectrum expected for the closo-dodecaborate anion 6 ), two signals were observed in the low field region (δ B 6.6 and 8.3) for slightly more concentrated (0.22 M) solution. Such concentration dependence of the 11 B NMR spectra was not observed in the case of compound 3.…”

“…Known cyclic oxonium derivatives 1 and 2, which can be easily prepared by reaction of the closo-dodecaborate anion with THF or 1,4-dioxane, 6 were selected as starting compounds, since these derivatives are known to react with nucleophiles to • C, 24 h.…”

“…6 We reasoned that a similar reaction with azide anion would lead to azido-functionalized derivatives of the closo-dodecaborate anion. Since the reaction should be performed in a non-aqueous solvent to prevent hydrolysis of the starting complexes, tetrabutylammonium azide (Bu 4 NN 3 )…”

“…11 B NMR spectra of 3 and 4 contained the set of signals (δ B − 22.8; −18.1; −16.8; 6.5) characteristic 6 of the closo-dodecaborate anion. Their IR spectra contained the characteristic absorption bands [2469 or 2465 cm −1 (BH) and 2099 or 2106 cm −1 (N 3 ), respectively in 3 and 4].…”

“…Compounds 1 and 2 were synthesized according to the published procedures. 6 Thin-layer chromatography was carried out on plates with silica gel 60 on aluminum foil (Merck). Spots of compounds containing boron hydride fragments were visualized with solution of PdCl 2 (1.256 g) in 10% aqueous HCl (25 ml) and MeOH (250 ml Tetrabutylammonium azide 7 To a solution of Bu 4 NHSO 4 (778 mg, 2 mmol) in water (1 ml) 10 M NaOH (0.3 ml) was added, followed by a solution of NaN 3 (260 mg, 4 mmol) in water (1 ml).…”