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

202 Silyl Radicals in Polymers and Materials
Irradiation (l > 300 nm) of a toluene solution of disilacyclobutane 38 with
C60 afforded the fullerene derivative 39 in a 61 % yield, resulting from an
unexpected rearrangement of the disilacyclobutane unit [41]. Also this reaction
mechanism is still unknown.
On the other hand, cyclotetrasilane 40 reacted with C60 under identical
experimental conditions, affording the 1:1 adduct 41 in an 87 % yield [42]. It
is worth underlining that the rearrangement of the cyclotetrasilane unit derived
from the addition of a silyl radical moiety to one of the terminal phenyl rings.
Photoreaction of C60 with higher homologous cyclic oligosilanes such as
(Ph2Si) 5, (Et2Si) 5 and (Me2Si) 6 has also been investigated using 254 nm excitation
[35]. In these cases, 1,4-addition products having the formula C60(SiR 2) 4
have been obtained.
Laser flash photolysis experiments showed that the 3 C 60 (Reaction 8.17)
reacts with cyclic oligosilanes 42, 43 and 44 in benzonitrile by an electron
transfer mechanism [43]. The rate constant (kET) for the three-membered cyclic
compound 42 is found to be 7:0 10 8 M 1 s 1 , whereas for the other two
compounds it was more than two orders of magnitute lower, i.e.,
(1–2) 10 6 M 1 s 1 .
R2 Si
R2Si SiR2 R2Si SiR2 R2Si SiR2 R2Si R2 Si
SiR2 R2Si SiR2 42, R = mesityl 43, R = i-Pr 44, R = Ph
The chemical reactivity of silylated fullerenes has hardly been explored. The
fluorescence quantum yield of 1,16-adduct 29 (R ¼ Ph, R 0 ¼ t-Bu) was found
slightly larger than that of C60, whereas its triplet excited state and quenching
rates were very similar to those of C60 [44]. From the silyl radical chemistry point
of view, it is worth underlining that the reaction of silylated fullerene 41 with
bromine in carbon disulfide under daylight irradiation, afforded C60 in a 90 %
yield, together with the unexpected 9,10-disilaanthracene derivative 47, whose
structure was determined by X-ray crystallography, in a 43 % yield (Scheme 8.9)
[45]. Although the reaction mechanism is unknown, the formation of intermediate
silyl radical 45 was suggested, which rearranges by intramolecular addition to
a pendant phenyl moiety to ultimately provide 46 (cf. Section 6.2). Further
oxidation of the central Si w Si bond is expected to give the observed product.
8.5 RADICAL CHEMISTRY ON SILICON SURFACES
Silicon is the most technologically important material utilized today owing to
its unique role in the fabrication of semiconductor devices and microprocessor
chips. The understanding and control of silicon surfaces is of great importance
in the production of silicon-based electronic devices, since the fraction of atoms