New Ways to a Series of Parent Representatives of the Eight‐, Nine‐, and Ten‐Vertex Monocarbaborane Family

The conditions for a reaction between nido‐B10H14 (1) and aqueous formaldehyde in an alkaline solution have been optimized, which resulted in the isolation of the [arachno‐6‐CB9H14]− anion (2) in 52% yield. Anion 2 was used as a convenient source for the synthesis of a series of basic monocarbaborane compounds. Thus, oxidation of 2 (Et4N+ salt) with I2 in CH2Cl2 in the presence of Et3N at room temperature afforded the [nido‐6‐CB9H12]− anion (3). Acidification of anion 2 (generated in situ from borane 1) with hydrochloric acid, in the presence of both FeCl3·6H2O and CH2O, led to the formation of arachno‐4‐CB8H14 (4), from which nido‐1‐CB8H12 (5) was obtained by dehydrogenation at 200 °C in quantitative yield. Compound 4 can easily be converted into the [closo‐1‐CB7H8]− anion (6) in 71% yield via reaction with Et3N and I2 in THF at −78 °C. Anion 6 is also formed in 75% yield by treatment of carborane 5 with Et3N in refluxing toluene. The [closo‐1‐CB8H9]− anion (7) was isolated by iodination of carborane 5 in the presence of Et3N (yield 81%) or by the heating of the PPh4+ salt of anion 2 at 220 °C (yield 95%). The structure of anion 2 was determined by an X‐ray diffraction study and the structures of compounds 2, 4, 5, and 7 were geometry optimized at the RMP2(fc)/6‐31G* level. The NMR spectroscopic measurements are in some cases complemented by unpublished 13C NMR spectroscopic data. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)