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

114 Addition to Unsaturated Bonds
Initiation steps:
AIBN
Propagation steps:
Termination steps:
∆, O 2
t-BuMe 2 SiOO
2 t-BuMe 2 SiOO
ROO
t-BuMe 2 SiH
t-BuMe 2 SiH
t-BuMe 2Si
t-BuMe2Si + O2 t-BuMe2SiOO +
t-BuMe 2 SiOOH
non-radical products
Scheme 5.13 Reaction mechanism of the oxidation of t-BuMe2SiH
+
t-BuMe 2 Si
for trialkylsilyl hydrides (cf. Chapter 2). Finally, the resulting silanol is suggested
to derive from the reaction of silylhydroperoxide with Co(II).
R 3 SiH
+ O 2
O
O
NO
60
O
O
NOH
Co(OAc) 2
R 3 SiOH
(5.47)
+ R3SiH 60 + R3Si (5.48)
Hydroxysilylation of alkenes with R3SiH under molecular oxygen was also
successfully achieved using 60 as catalyst [93]. Reaction (5.49) shows two
examples using Et3SiH where the conversion is ca. 60% and selectivity higher
than 90%. Similar results were obtained with Ph3SiH whereas (TMS)3SiH
afforded only hydrosilylation products. It was suggested that Reaction (5.48)
is one of the propagation steps. Consecutive additions of silyl radical to alkene
and of the adduct radical to oxygen afford a peroxyl radical that it expected to
be the precursor of the isolated product.
R + Et3SiH + O2 60 (cat.)
Co(OAc) 2
Et3Si OH
R
(5.49)
R = CN or CO2Me 60 �C
>90%