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

70 Reducing Agents
expected in the future, especially in the synthesis of natural products and
pharmacologically active compounds.
(TMS) 3SiH reacts spontaneously and slowly at ambient temperature with
molecular oxygen to form siloxane as the sole product (Reaction 4.48) [84]. This
reaction, which occurs via a radical cascade reaction, will be discussed in detail
in Chapter 8. Two aspects of the autoxidation of (TMS) 3SiH are of interest to
synthetic chemists: (i) for radical reactions having long chain lengths, traces of
molecular oxygen can serve to initiate reactions, therefore no additional radical
initiator is needed, and (ii) the oxidized product does not interfere with radical
reactions, therefore the reagent can be used even if partially oxidized, taking
into account the purity of the material. In our experience, commercially available
materials are ca 98 % pure by GC analysis. This analytical method can also
be used for a titration of the reagent, thus giving the exact concentration of
silane for kinetic purposes.
(Me3Si) 3SiH þ O2 !(Me3SiO) 2Si(H)SiMe3 (4:48)
4.4 OTHER SILICON HYDRIDES
4.4.1 TRIALKYLSILANES
Trialkylsilanes are not capable of donating the hydrogen atom at a sufficient rate
to propagate the chain. As reported in Section 3.1.1, the attack of primary alkyl
radicals on Et3SiH occurs in about 60 % of cases at the SiH moiety and 40 % at
the ethyl groups at 130 8C. Therefore, chain reactions are not supported under
normal conditions, although trialkylsilyl radicals are among the most reactive
species toward various organic functional groups (see below). Early work based
on the reduction of polychloroalkanes by trialkylsilanes, using dibenzoyl peroxide
as the initiator, gathered the relative rates of hydrogen abstraction from
Si w H moiety and structural information about silyl radicals (see Chapter 1)
[85]. Triethylsilane reacts with polyfluorinated halocarbons under free radical
conditions initiated by thermal decomposition of peroxides. For example, 1,2dichlorohexafluorocyclobutane
reacts with an excess of Et3SiH, affording the
dihydro derivative in excellent yield (Reaction 4.49) [86]. Primary or secondary
substituted acyl chlorides, RC(O)Cl, in the presence of di-tert-butyl peroxide at
140–170 8C gave the corresponding RH in 50–70 % yields [87]. Similarly, chloroformates,
ROC(O)Cl afforded the corresponding RH in good yields [88].
F 6
Cl
Cl
Et 3SiH
[PhC(O)O] 2
120 �C, 13h
F 6
H
H
95%
(4.49)