(
)
J.-i. Ishikawa et al.rJournal of Organometallic Chemistry 552 1998 303–311
311
Ž
.
Ž .
LiAlH On–Bu would be changed into a more active hydride as shown in Eq. 9 , and catalyze the dehydrogenative
3
cross-coupling reaction.
PhSih qLiAlH Ot–Bu 3 ™LiAlH
Ot–Bu 3yx qPhSiH
Ot–Bu
9
Ž .
Ž
.
1qx Ž
.
3yx Ž
.
x
3
Ž
.
LiAl C[C–Ph P2THF also catalyzed the dehydrogenative cross-coupling reactions of phenylsilane with EB to
4
w
give the same products as LiAlH4. When 1-hexyne was used instead of EB, a dehydrogenated product n-
BuC[CSi Ph H2 was produced with a larger conversion of 1-hexyne than that of phenylsilane expt. no. 12 in Table
Ž
.
x
Ž
.
Ž
.
1 . The exchange reaction as shown in Eq. 10 would occur. These facts support the mechanism of the
Ž .
dehydrogenation reaction shown in Eq. 6 .
LiAl C[C–Ph q x HC[CyC H ™LiAl C[C–Ph
C[C–C H x q x HC[C–Ph
10
Ž
.
Ž
.
4yx Ž
.
Ž
.
4
4
9
4
9
The reaction under atmospheric pressure is more selective against the dehydrogenative cross-coupling reaction than
Ž
.
that at high pressure based on the equilibrium consideration compare expt. no. 1 with 5 in Table 1 . In expt. nos. 5, 6
Ž
.
Ž
.
reaction under closed system and 9 reaction under LiBH4 in Table 1, a small amount of styrene was also produced
by the hydrogenation of EB, and the conversion of EB was larger than that of phenylsilane.
As expected, the polymers of poly phenylsilylene ethynylene-1,3-phenylene ethynylene and
poly phenylsilylene ethynylene-1,4-phenyleneethynylene were obtained by the reaction of phenylsilane with m-DEB
w
Ž
.
x
w
Ž
.
x
wŽ
.
x
and p-DEB, respectively. Poly phenylsilylene ethynylene-1,3-phenyleneethynylene showed slightly less thermal
w
x
stability than MSP when prepared using the MgO catalyst 10,11 . The polymer prepared using LiAlH4 would contain
some C5C bonds in the molecule, which would be synthesized by the hydrosilylation reaction, though no peak
assigned to the C5C bond was observed in the spectra. The advantage of using LiAlH4 as the catalyst is lower
w x
Ž
.
amount of catalyst is needed than when using MgO 9 expt. no. 13 in Table 1 . Further studies will be needed to
determine which process is more industrially advantageous.
Ž
.
Ž
Ž
.
.
R3Si–H could be activated by transition metal complexes MLn to make Si–M and M–H bonds R3Si–M Ln –H .
We have shown that ionic compounds such as LiAlH4 and MgO catalyze the reactions concerning hydrosilanes. This
might suggest that the Si–H bond could be more easily polarized and activated to make an ionic state than the C–H
bond. We are now making an effort to study other reactions catalyzed by an ionic catalyst and other new ionic
catalysts.
Acknowledgements
This work was performed by Mitsui Toatsu Chemicals under the management of the Japan High Polymer Center as
a part of the Industrial Science and Technology Frontier Program supported by the New Energy and Industrial
Technology Development Organization.
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