Building a Lewis Base with Boron

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Science  29 Jul 2011:
Vol. 333, Issue 6042, pp. 530-531
DOI: 10.1126/science.1209588

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  1. Boron as a base.

    Boron compounds normally are acids that accept electron pairs, but Kinjo et al. show how to stabilize an electron pair on a boron center so that it forms a base—a borylene compound. The parent borylene A (R = H) is linear and sp-hybridized, and the lone pair is in an sp orbital. It accepts two electron pairs from two carbenes, yielding a neutral, three-coordinate boron Lewis base 1 (now trigonal planar and sp2-hybridized, with the lone pair now in a p orbital). The favored resonance structure 1a bears a lone pair of electrons at boron. In 1b, the two valence electrons of boron involves a B=C double bond. Related to 1, carbene-stabilized neutral diborenes B and boryllithium C represent other important three-coordinate boron(I) compounds. Dipp, 2,6-diisopropylphenyl; L:, N-heterocyclic carbenes; R denotes hydrogen, alkyl, aryl, or halides; boron, red.