Easy access to nucleophilic boron through diborane to magnesium boryl metathesis

Pécharman, Anne-Frédérique and Colebatch, Annie L. and Hill, Michael S. and McMullin, Claire L. and Mahon, Mary F. and Weetman, Catherine (2017) Easy access to nucleophilic boron through diborane to magnesium boryl metathesis. Nature Communications, 8. 15022. ISSN 2041-1723 (https://doi.org/10.1038/ncomms15022)

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Organoboranes are some of the most synthetically valuable and widely used intermediates in organic and pharmaceutical chemistry. Their synthesis, however, is limited by the behaviour of common boron starting materials as archetypal Lewis acids such that common routes to organoboranes rely on the reactivity of boron as an electrophile. While the realization of convenient sources of nucleophilic boryl anions would open up a wealth of opportunity for the development of new routes to organoboranes, the synthesis of current candidates is generally limited by a need for highly reducing reaction conditions. Here, we report a simple synthesis of a magnesium boryl through the heterolytic activation of the B–B bond of bis(pinacolato)diboron, which is achieved by treatment of an easily generated magnesium diboranate complex with 4-dimethylaminopyridine. The magnesium boryl is shown to act as an unambiguous nucleophile through its reactions with iodomethane, benzophenone and N,N′-di-isopropyl carbodiimide and by density functional theory.