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

BuC=CH + H,B·THF----> BuCH 2 CH(B <) 2
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Organoboron compounds
The carbonylation of organoboranes presumably proceeds via a weak complex
R 3 B · CO which rearranges in a similar way to an acylborane. This can be
converted as shown into a variety of organic products. In severa! of these
reactions, however, only one or two of the three R groups on boron are used.
Similarly alkynyltrialkylborate ions. on protonation and oxidation yield
ketones or tertiary alcohols according to the conditions.
HCI R~ H20 2/
/C=CH2
R 2 B 1
aq.HCI
OH
RCOCH 3 (ketone)
RB-CR2CH3
1
H202/
OH
OH OH
R2CCH 3 ( terliory olcohol)
As well as being hydroborating agents, boron hydrides can reduce certain
functional groups. In Table 3.8 the behaviour of BH 1 and of 9-BBN in THF is
compared with that of some other common hydridic reagents. It is therefore
necessary to 'protect' groups such as -CHO, -COR and -CN ifthey are present
in a molecule which it is intended to hydroborate.
The hydroboration of alkynes leads in the first instance to alkenylboranes. In
the absence of sufficient steric effects, however, these react further. Using
H 3 B · THF, for example, 1-alkynes give predominantly diboron derivatives.
1