Recent developments of boryl anions: Boron analogues of carbanion

Abstract

This account reviews the chemistry of "boryl anion." Boryl anions can be classified with their metallic counterpart, such as Li, Mg, Cu, and Zn in a similar manner to the classification of carbanions. The early attempts to generate boryl anions by reductive dehalogenation of haloboranes with alkali metal or photolysis of tetraphenylborate compounds had no modern spectroscopic identification of the reactive "boryl anion." Recent developments of base-stabilized boryl anion, base-BH2-M+ (base = NEt3 or PCy3, M = K or Li), and generation of borylcopper species, "pinBCuL," have opened a new area of organoboron chemistry. Recently, we have synthesized a lithium salt of boryl anion, boryllithium, which reacted with electrophiles as a boron nucleophile. Based on the high reactivity of boryllithium, transmetallation to other metals enables synthesis of a series of borylmetals, such as borylmagnesium, borylcopper, and borylzinc species. All of these compounds were isolated and structurally characterized to have an sp2 boron atom. Reactivity with organic electrophiles could confirm that they behaved as boron nucleophiles. © 2008 The Chemical Society of Japan.