amounts in many cases. Despite the recent progress,
there is still a strong need for a highly efficient synthetic
method for the conversion of readily available organosi-
lanes to silanols. One of the authors has recently reported
a highly selective and practical ruthenium-catalyzed
hydrolytic oxidation of organosilanes to the corresponding
silanols under relatively mild conditions.8 To continue our
studies on the development of new metal-catalyzed
reactions using organosilanes,9 we reveal herein an
additional catalytic oxidation protocol of organosilanes
to the corresponding silanols with excellent selectivity
and efficiency under mild conditions.
High ly Efficien t Ir id iu m -Ca ta lyzed
Oxid a tion of Or ga n osila n es to Sila n ols
Youngjun Lee,† Dong Seomoon,† Sundae Kim,†
Hoon Han,‡ Sukbok Chang,‡ and Phil Ho Lee*,†
Department of Chemistry, Kangwon National University,
Chunchon 200-701, Republic of Korea, and Department of
Chemistry, Korea Advanced Institute of Science and
Technology, Daejeon 305-701, Republic of Korea
phlee@kangwon.ac.kr
The catalytic activity of several transition metals was
examined for the conversion of triethylsilane to trieth-
ylsilanol with the use of water as an oxygen source for
practical reasons. The sterically exposed silane was
chosen as a model compound because its oxidation to the
corresponding silanol is highly sensitive to the reaction
conditions, and condensation to disiloxane is a serious
drawback frequently encountered in most reported
procedures.4-6,10 Of the catalytic systems screened, the best
Received November 9, 2003
Abstr a ct: Hydrolytic oxidation of organosilanes to the
corresponding silanols can be performed highly efficiently
with a catalyst system of [IrCl(C8H12)]2 under essentially
neutral and mild conditions, and various types of silanols
are produced in good to excellent yields.
11
result was obtained with 1 mol % [IrCl(C8H12)]2 in the
Development of concise methods for the preparation
of silanols is highly valuable in the field of synthetic
organic chemistry1 because organosilanols can be utilized
both in organic synthesis as versatile building blocks and
in industry for the production of silicon-based polymeric
materials.2 In addition, organosilanols have been recently
used as a nucleophilic coupling partner in Pd-catalyzed
cross-coupling reactions.3 A variety of preparative pro-
cedures of silanols have been developed, including hy-
drolysis of chlorosilanes,4 oxidation of organosilanes with
stoichiometric amounts of oxidants,5 and treatment of
siloxanes with alkali metal reagents.6 However, most
known methods have a limited scope because silanols are
sensitive to dimerization in the presence of even trace
amounts of acid or base which are normally found in the
reported procedures. Recently, catalytic oxidation of the
Si-H bond of organosilanes has been studied extensively
with Ni, Pd, Cr, Rh, Re, and Cu complexes.7 However,
these protocols exhibit a rather limited scope to certain
substrate types and they produce disiloxanes in high
presence of 2 equiv of H2O at room temperature, under
which triethylsilanol was isolated in 80% yield. There was
no disiloxane formed from the reaction. Other iridium
complexes such as IrCl(CO)(PPh3)2 and [Ir(C8H12)2]+BF4
-
produced triethylsilanol in low yield. CH3CN was the
solvent of choice among several reaction media screened.
Triphenylsilane was oxidized to triphenylsilanol using
8
[IrCl(C8H12)]2 and [RhCl2(p-cymene)]2 to compare the
reactivities of these catalysts. Although triphenylsilanol
was obtained in 10% yield with 1 mol % [RhCl2(p-
cymene)]2 in CH3CN at 25 °C for 24 h, the corresponding
silanol was produced in 83% yield with 1 mol % [IrCl-
(C8H12)]2 in CH3CN at 25 °C for 2 h. Therefore, [IrCl-
(C8H12)]2 is a much more reactive catalyst than [RhCl2-
(p-cymene)]2 toward oxidation of silanes.
To demonstrate the efficiency and scope of the present
method, we applied the Ir-catalytic system to a variety
of organosilanes. Organosilanols were obtained in good
to excellent yields across a variety of organosilanes under
the optimum conditions (Table 1). Sterically exposed
silanes were smoothly oxidized to silanols in high yields
under mild conditions. Selectivity for the formation of
silanol versus disiloxane was excellent even for the
* Corresponding author. Phone: +82 33 250 8493. Fax: +82 33 253
7582.
† Kangwon National University.
‡ Korea Advanced Institute of Science and Technology.
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10.1021/jo035647r CCC: $27.50 © 2004 American Chemical Society
Published on Web 02/03/2004
J . Org. Chem. 2004, 69, 1741-1743
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