Identification of an intermediate in the deboronation of ortho-carborane: an adduct of ortho-carborane with two nucleophiles on one boron atom

Abstract

The 1 : 2 adduct of 1-bromo-ortho-carborane and pyridine has been identified as a significant intermediate in the deboronation of ortho-carborane to a nido-anion.

Synthesis and Reactivity of 4,5‐[1,2‐Dicarba‐closo‐dodecaborano(12)]‐1,3‐diselenacyclopentane: Opening of the Icosahedron to Give a Zwitterionic Intermediate and Conversion into 7,8‐Dicarba‐nido‐undecaborate(1−)

“…Similarly, other structural parameters calculated for the model compounds agree well with the experimental data determined here. Some of the structural parameters reported for 10 [26] were not reproduced by the calculations, and these data are also at variance with experimental data found for 6 (Table 4). (Table 2) are generally well reproduced by calculations.…”

“…An important question concerns the equilibrium between the zwitterionic intermediate 6 and the carborane 4. This issue had not been addressed in previous work on the C À Br ortho-carboranes, [26] in which it had been pointed out that the 7,8-dicarba-nido-undecaborate(1À) that corresponded to 5 is the sole final product. When the pure compound 6 b ( Figure 6A) was dissolved in CD 2 Cl 2 and the solution was kept at RT for prolonged periods of time, the NMR spectra ( Figure Finally, it seemed advisable to look for independent proof of the identity of the 7,8-dicarba-nido-undecaborate(1À) 5 (Scheme 3).…”

“…[26] Apparently, ortho-carborane 1 itself does not react with pyridine. [26] In the present work, we have isolated and fully characterized the intermediate 6 in solution and in the solid state. In contrast to previous work on C À Br deriva- …”

“…www.chemeurj.org tives, [26] the results of the X-ray diffraction study are conclusive, and the solution-state Se NMR spectra were fully assigned. Moreover, we have obtained evidence that the opening of the icosahedron in 4 by its reaction with pyridine to give 6 is a reversible process (vide infra).…”

“…[26] The nido-type structure of 10 had been proposed on the basis of an X-ray structural analysis; [26] however, some of the structural parameters appeared to be unreliable, since the positions of two boron atoms were not clearly defined. [26] Apparently, ortho-carborane 1 itself does not react with pyridine.…”