_P.-Powell-auth.-Principles-of-Organometallic-Chemistry-Springer-Netherlands-1988

Organoboron compounds
are white crystalline solids which are slowly attacked by oxygen; the aryl
analogues are essentially air-stableo Dehydrationo carried out by azeotropic
removal of water under reflux in benzene or toluene using a Dean-Stark
apparatus,leads to the cyclic trimeric anhydrides or boroxines, (RBO) 3 o The lower
alkylboron chlorides are not very convenient to handle; they are spontaneously
inflammable in air and very sensitive to moistureo Moreover their specific
preparation from BCl, or R 3 B is difficult; some R 2 BCl is usually formed as wello
Consequently other routes to boronic and borinic acids have been developedo
Trialkylborates (trialkoxyboranes) react with Grignard reagents to give, after
hydrolysis, alkylboronic acids, but yields often are rather low on account of the
formation of some R 2 BOH and R 3 B as wello
B(OMe), + RMgX
i)ether, -7R''C
--------> RB(OH) 2 ( + R 1 BOH + R,B)
liilH,o+
Alkylboronic acids can be purified by conversion into diethanolamine chelates,
which are crystalline air stable materialso Note that intramolecular coordination
of nitrogen to boron gives the latter an octet configurationo Similarly dialkylborinic
acids may be converted into chelate derivatives with 2-aminoethanol.
ozeot ropic
distillotion
-H20
Monoalkylboron compounds may be obtained by hydroboration using
catechol borane or Me 2 SoBHCl 2 o
OCOH
OH
+ BH3.THF
THF
-2H2
OC o"-
/
o
BCH H2o
2 CH 2 R ---+ RCH 2 CH 2 B(OH) 2 + catechol
The former is obtained from catechol (1. 2-dihydroxybenzene) and borane in
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