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

The first three periodic groups
Table 3.8. Summary ofbehaviour ofvarious functional groups towards hydridic reagents
Functional/ Reagent NaBH 4 BH, 9-BBN LiEt,BH LiAIH 4
Group Solvent EtOH THF THF THF THF
-CHO + + + + +
-COR + + + + +
-COC! attacks
solvent + + +
-CO,R ± ± + +
-CO,H + ± +
-CN + ± + +
-NO, + +
C=C + +
+ reaction occurs; - no reaction; ± borderline, reaction often slow.
The problem is largely overcome by the use of bulky hydroborating agents,
careful regulation of reaction conditions and if necessary, the use of excess of
alkyne. The resulting alkenylboranes are useful synthetic intermediates.
EtC:: CEt g-BBN
Et, Et
"c=c/
/ "
H rJ\ Et Et
Et, /Et / '(_) ~ )c=c(
~~ H H
/ "'
H Hg(OMe)
(non catalytic
cis-hydrogenatior
of-C:C-)
Vinyl mercurials
3.8.2 Lewis acidity of boranes
Studies of the coordination compounds of boron, especially of its halides, alkyls
and hydrides, ha ve contributed substantially to our understanding of the factors
which influence the stability of coordination compounds in general. The factors
which particularly concern boron complexes are inductive and steric effects and
reorganization energies, as explained below.
(a) INDUCTIVE ANO STERIC EFFECTS. The formation of a coordination compound
between, for example, a borane and an amine according to the equation
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