"Front Matter". In: Organosilanes in Radical Chemistry - Index of

Carbon–Carbon Triple Bonds 97
[34]. Reaction (5.14) shows that the silane-addition products of terminal alkenes
are obtained in moderate yields. The reaction mechanism starts from the bisallylic
hydrogen of cyclohexadiene 16, which is abstracted by the initiator,
leading to a cyclohexadienyl radical. The aromatization of the intermediate
(which can be read as the reversibility of silyl radical addition to aromatic
species) then provides the t-BuMe2Si: radical. Another source of silyl radicals
for hydrosilylation reactions, although not in a high yield, has been envisaged
as the organosilylborane PhMe2Si w B[N(CHMe) 2] 2 treated by continuous irradiation
with a high-pressure mercury lamp (cf. Section 1.1) [35].
X
X = CH 2 Ph or OC(O)Me
Me SiMe2Bu-t MeO OMe
16
AIBN, 80 �C
t-BuMe 2 Si
55%
X
(5.14)
The reaction of Et3SiH with [1.1.1]propellane under photolytical decomposition
of di-tert-butyl peroxide afforded products 17 and 18 in 1:3 ratio (Reaction
5.15) [36]. A rate constant of 6:0 10 8 M 1 s 1 at 19 8C for the addition
Et3Si: radical to [1.1.1]propellane was determined by laser flash photolysis [37].
Thus, it would appear that [1.1.1]propellane is slightly more reactive toward
attack by Et3Si: radicals than is styrene, and significantly more reactive than
1-hexene (cf. Table 5.1).
Et 3 SiH
t-BuOOBu-t, hν
5.2 CARBON–CARBON TRIPLE BONDS
Et3Si H +
Et2HSi H
17 18
40%, 17:18 = 1:3
5.2.1 FORMATION OF SILYL RADICAL ADDUCTS
(5.15)
As with alkenes, the addition of silyl radicals to a carbon–carbon triple
bond (Reaction 5.16) is also the key step in the hydrosilylation of alkynes
[9,10].
R3Si + R' R''
R 3 Si
R'
19
R''
(5.16)