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

5 Addition to Unsaturated Bonds
Hydrosilylation is a term describing an addition of organic and inorganic silicon
hydrides to carbon–carbon or carbon–heteroatom multiple bonds. The hydrosilylation
of a carbon–carbon double bond was first reported in 1947 as a freeradical
process [1] and became important both in industry and in the laboratory
during the fifties and sixties for the production of organosilicon compounds [2].
Good yields were obtained for chlorinated silanes such as Cl3SiH and
Cl2Si(H)Me in the presence of thermal decomposition of various peroxides
[1,2], whereas the failure of alkyl or aryl substituted silanes to give similar
products was due to their inefficiency of hydrogen donation to alkyl radicals
[3]. The radical-based methodology was later superseded by the introduction of
transition metal catalysts [2,4,5]. Catalytic hydrosilylation has been exploited in
all directions and today represents a fundamental and elegant methodology for
both academic and industrial synthetic chemists [6,7]. Nevertheless, the introduction
of a variety of organosilanes in the nineties with different hydrogen
donor abilities (see Chapter 3) has made the radical-based hydrosilylation flourish
again not as an alternative to catalytic methods, but as a complementary
approach. Furthermore, the radical-based hydrosilylation of silicon surfaces has
also been studied intensively in the last few years because of its crucial importance
in modern technology. The most salient aspects of monolayer formation on
silicon using this methodology are discussed in Chapter 8.
The initiation and propagation steps for the radical-based hydrosilylation of
carbon–carbon double bonds are reported in Scheme 5.1 [8]. The initially
generated radicals (In:) abstract a hydrogen atom from the R3SiH. The
resulting R3Si: radical adds to the double bond to give a radical adduct,
which then reacts with the silicon hydride and gives the addition product,
together with ‘fresh’ R3Si: radicals to continue the chain. Chain reactions
Organosilanes in Radical Chemistry C. Chatgilialoglu
# 2004 John Wiley & Sons, Ltd ISBN: 0-471-49870-X