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

The conditions for a reaction between nido ‐B 10 H 14 ( 1 ) and aqueous formaldehyde in an alkaline solution have been optimized, which resulted in the isolation of the [ arachno ‐6‐CB 9 H 14 ] − 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 (Et 4 N + salt) with I 2 in CH 2 Cl 2 in the presence of Et 3 N at room temperature afforded the [ nido ‐6‐CB 9 H 12 ] − anion ( 3 ). Acidification of anion 2 (generated in situ from borane 1 ) with hydrochloric acid, in the presence of both FeCl 3 ·6H 2 O and CH 2 O, led to the formation of arachno ‐4‐CB 8 H 14 ( 4 ), from which nido ‐1‐CB 8 H 12 ( 5 ) was obtained by dehydrogenation at 200 °C in quantitative yield. Compound 4 can easily be converted into the [ closo ‐1‐CB 7 H 8 ] − anion ( 6 ) in 71% yield via reaction with Et 3 N and I 2 in THF at −78 °C. Anion 6 is also formed in 75% yield by treatment of carborane 5 with Et 3 N in refluxing toluene. The [ closo ‐1‐CB 8 H 9 ] − anion ( 7 ) was isolated by iodination of carborane 5 in the presence of Et 3 N (yield 81%) or by the heating of the PPh 4 + 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 The NMR spectroscopic measurements are in some cases complemented by unpublished 13 C NMR spectroscopic data. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)