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

192 Silyl Radicals in Polymers and Materials
Me
Me3Si Si
H
SiMe3 + O2 Me3Si O
Me
Si
H
O SiMe3 (8.5)
Tetrakis(trimethylsilyl)silane, (Me3Si) 4Si, cannot be oxidized under the same
conditions [18]. This excludes any direct insertion of an oxygen molecule on the
Si w Si bond followed by a molecular rearrangement.
Oxygen-labelling experiments were also performed in order to distinguish
whether the two oxygen atoms in the final product arise from two different oxygen
molecules or from the same oxygen molecule. Both (Me3Si) 3SiH and
(Me3Si) 2Si(H)Me were treated with a mixture of 16 O2 and 18 O2 (Reaction 8.6) and
the crude products were analysed by mass spectrometry to determine the isotopic
distribution. The fact that similar label distribution was observed in the products
as in the reactants for both cases, indicates an intramolecular mechanism, i.e., two
oxygen atoms in the final product arise from the same oxygen molecule [15,18].
Me3Si R
Si
H
SiMe3 +
( 16O-16O / 18 18 - )
Me3Si O
R
Si
H
O SiMe3 +
Me3Si R
Si
H
SiMe3 The reaction sequence shown in Scheme 8.4 is in accord with all the experimental
observations and involves at least two consecutive unimolecular steps
[15,18]. Silyl radical 11 adds to molecular oxygen to form the peroxyl radical 12.
Me3Si O
R
Si
H
O SiMe3 Me3Si R
Si
H
SiMe3 Me3Si O
R
Si O SiMe3 14
Me3Si R
Si SiMe3 Me3Si R
Si
O
O
13
11
SiMe 3
O 2
Me3Si R
Si
O
SiMe3 O
12
Scheme 8.4 Proposed propagation steps of the autoxidation of silicon hydrides containing at
least two silyl substituents (R ¼ Me or SiMe3)
(8.6)