Brellochs reaction

While alkynes, nitriles, and isocyanides have long been known to insert a cage carbon into polyboranes (COMC (1982) 5.4.2.6.1 and 5.4.2.6.2), the use of aldehydes to insert a cage carbon was first reported by Bernd Brellochs in 1997 (Figure 5).86 Good yields of 10-vertex monocarbaboranes were obtained from B10H14 with KOH and many aldehydes and this reaction was thus coined the Brellochs reaction. 87... 

The Brellochs reaction represents a significant breakthrough in monocarbaborane chemistry, the exploration of which was previously limited by multistep routes. For example, the important carborane anion CBnFI12 can now be made in two steps with an overall yield of 66%.88 Its synthesis previously required three steps involving undesirable compounds such as hydrogen cyanide, dimethylsulfate, and trialkylamine. (COMC (1982) 5.4.2.6.2) The arachno-cztbotznc... 

Figure 5 Important carboranes accessible from B10H14 via the Brellochs reaction.

The material reviewed in this Chapter hitherto has focused on metallacarboranes in which the metal atom is a vertex in an icosahedral cage framework. Until recently, monocarbollide metal compounds with core structures other than 12 vertexes were very rare since suitable carborane precursors were not readily available." However, Brellochs recent development of the reaction of decaborane with aldehydes to give 10-vertex monocarboranes permits a considerable expansion in this area of boron cluster chemistry. As a consequence, several intermediate-sized monocarboranes are now easily accessible and we have recently begun to exploit the opportunities that these present. In particular, we have focused thus far on complexes derived from the C-phenyl-substituted species [6-Ph- zJo-6-CBgHii] It is clear from these initial studies that a wealth of new chemistry remains to be discovered in this area, not only from among the metal derivatives of PhCBg car-boranes such as those discussed in this section, but also in the metal complexes of other newly available carboranes. 

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