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

78 Reducing Agents
An interesting variant of the above mentioned reaction is the use of 1,1,2,2tetraphenyldisilane.
The reductions of alkyl bromides [110], phenyl chalcogenides
[111] and xanthates [112] have been performed using either AIBN in
refluxing ethanol or Et3B=O2 at room temperature. Yields varied from moderate
to excellent, depending on the experimental conditions. Two examples with
3-cholestanyl bromide and 2-phenylseleno sugar are given in Reaction (4.70)
and (4.71). Disilanes having para-fluoro or para-methoxy phenyl substituents
showed similar reactivities [110–112].
Br
Ph Ph
Ph Si Si Ph
H H
(2.4 equiv)
Et 3B, O 2, r.t.
(4.70)
99%
OAc
Ph
Ph Ph
Si Si Ph
OAc
AcO
O
OEt
H H
(2.4 equiv)
AcO
O
OEt (4.71)
Et3B, O2 , r.t.
AcO SePh
AcO
79%
4.4.4 ALKYLTHIO SUBSTITUTED SILICON HYDRIDES
Substitution at the SiH moiety has been carried out with alkylthio groups, such
as MeS and i-PrS. Tris(alkylthio)silanes, (RS) 3SiH, are radical-based reducing
agents which can effect the reduction of bromides, iodides, xanthates, phenylselenides
and isocyanides in toluene, using AIBN at 85 8C as the initiator
(Reaction 4.71) [113]. The reduction of chlorides is efficient only when astabilizing
groups or gem-dichlorides are present. It is interesting to note that
under the reduction conditions and in the absence of substrates the reagent is
consumed, forming (RS) 4Si, probably by a SH2 reaction at the sulfur atom
[113]. By replacing a Me3Si group in (TMS) 3SiH with the thiol group Me3SiS,
the resulting silicon hydride behaves similarly (Reaction 4.72) [114]. Thiolsubstituted
silicon hydrides have not found an application in synthetic procedures
so far, probably due to their unpleasant smell.
X
(MeS) 3 SiH
AIBN, 85 �C
>96%
X=Br, I, OC(S)SMe, SePh, CN −
(4.71)