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6.1.38 Product Subclass 38: Trialkylboranes

DOI: 10.1055/sos-SD-006-00903

Zaidlewicz, M.; Krzeminski, M.Science of Synthesis, (200561097.

General Introduction

The synthesis and chemistry of trialkylboranes has been extensively reviewed in HoubenWeyl, Vol.13/3a, and in monographs and articles.[‌1‌‌13‌] The electronegativity of boron (2.0) and carbon (2.5) are similar.[‌14‌] The BC bond is essentially covalent and its length is almost the same as the CC bond (trimethylborane[‌15‌] 156pm, ethane[‌16‌] 153.4pm). Trialkylboranes are monomeric and can be readily isolated. Generally, they are thermally stable and do not decompose over prolonged periods at room temperature; however, at elevated temperatures (>100°C) they undergo isomerization, the boron atom migrating to the less hindered position.[‌17‌] Some hindered trialkylboranes undergo isomerization at lower temperatures. Trialkylboranes are poor nucleophiles when compared to organolithium and organomagnesium compounds; they do not readily react with typical electrophiles, including alkyl halides, epoxides, aldehydes, ketones, esters, amides, and nitriles. They are not sensitive to protonating agents such as water, alcohols or even dilute mineral acids, and they are not readily hydrolyzed. The low nuclephilicity of trialkylboranes renders them tolerant of a variety of electrophilic functional groups. Functionalized trialkylboranes can be prepared and used in CC and carbonheteroatom bond-forming reactions.

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