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The Diverse World of Silicon Chemistry.

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Meeting Reviews
The Diverse World of Silicon
Chemistry**
Guido Kickelbick*
Besides carbon, the only other element
that reveals a similarly rich chemistry is
silicon, spanning classical main-group to
organometallic to materials chemistry,
biochemistry and biotechnology, as well
as theoretical chemistry. Although both
elements have many properties in
common, silicon often reveals a remarkably different reactivity compared to
carbon. The extraordinary properties of
silicon and the large variety of products
that can be prepared given its similarity
to carbon make it not only a prominent
element in academic research but also in
industry, where its value has been recognized, for example, in polymers and as
a semiconductor material.
The particular reactivity of silicon
and its highly innovative chemistry are
also reflected by the fact that a conference series celebrated its 40 year tradition, namely, the 14th International
Symposium on Organosilicon Chemistry. Hundreds of scientists gathered in
W(rzburg (Germany) to discuss
ground-breaking news in the field of
silicon chemistry. For the first time, this
meeting was held in conjunction with
the European Organosilicon Days. The
exceptional characteristic of this meeting series was the close contact between
scientists from both academia and
[*] Dr. G. Kickelbick
Vienna University of Technology
Institute of Materials Chemistry
Getreidemarkt 9-165
A1060 Vienna (Austria)
E-mail: kickelgu@mail.zserv.tuwien.ac.at
[**] 14th International Symposium on Organosilicon Chemistry (ISOS XIV) in conjunction with the 3rd European Organosilicon Day in W8rzburg (Germany), 31st
July to 5th August, 2005.
6804
industry as well as the variety of
research from both areas, as evident
from the composition of the lecture
program which covered all of the
above-mentioned aspects of silicon
chemistry. The scientific program
included more than 150 talks and over
220 posters.
Silicon chemistry still is mainly
driven by the interest to compare the
similarities and differences in its reactivity relative to that of carbon. A major
challenge is the synthesis of Si Si multiple bonds. A pioneer in this area is
Mitsuo Kira (Tohoku University,
Sendai, Japan), who presented an overview of the latest developments in the
field of dialkylsilylenes and Si=Si
double-bonded compounds, such as spiropentasiladiene
and
trisilaallene
(Scheme 1). Kira and co-workers suc-
Toronto, Canada) revealed the many
possible applications of polyferrocenylsilanes. These metal-containing polymers that are produced by ring-opening
polymerization reveal a controllable
structure, which facilitates the control
over their self-organization. The resultant supramolecular metal-containing
structures can be used, for example, as
magnetic materials. Application of UV
photolithography allows the use of polyferrocenylsilanes for the patterning of
thin films, which can be additionally
metalated by binding cobalt carbonyl
compounds.[2, 3] Catalytic cross-dehydrocoupling reactions of silanols and silanes
represent a route to novel siloxanebased polymers. Yusuke Kawakami
(Japan Advanced Institute of Science
and Technology, Nomi, Japan) and coworkers have used tris(pentafluorophenyl)borane as an effective catalyst
for the synthesis of such polymers.[4] Patterning of siliconbased materials is regularly carried out by applying the selforganization of amphiphilic macromolecules. Ulrich Wiesner
(Cornell
University,
Ithaca,
USA) and his team make use of
the organization of amphiphilic
block copolymers in complex
three-dimensional structures as
templates to perform chemistry
in the formed domains. By application of this method, it is possible
to produce three-dimensional
silica-based structures as well as
Scheme 1. Some extraordinary Si compounds proSiCN- and SiC-based systems,
duced by Kira’s group.[1]
which can be viewed as the reproduction of the previously formed
ceeded in isolating stable disilene in the
structures.[5, 6]
form of the silicon analogues of cycloNicola H(sing (University of Ulm,
propene and cyclobutene.[1] Further Germany) demonstrated new possibilhighlights from Kira8s laboratory were ities of the structuring of sol–gel-based
the first stable compound with a formal materials using tetrakis(2-hydroxysp-hybridized silicon atom, cross-conju- ethyl)silane as precursor, which releases
gated Si=C compounds, and 1,3- glycol instead of an alcohol during
disilabicyclo[1,1,0]butane as the first hydrolysis and condensation.[7] The use
isomer with an inverted bridged Si Si of a drying process, which leads to a
bond. In honor of his pioneering work in more-hydrophobic surface, helps to prothis field, Kira was awarded the 2005 duce highly porous monoliths.[8] Besides
Wacker Silicon Award in W(rzburg.
pure oxidic materials, organically modiResearch in the field of silicon-con- fied silsesquioxanes have become an
taining polymers is currently fuelled by important topic of research in recent
an interest in controlling their composi- years. Speculations that were often reation and morphology as well as the sons for scientific discussion about the
patterning of materials by using macro- structure of ladder-type silsesquioxanes
molecules. Ian Manners (University of produced by the sol–gel process of
2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2005, 44, 6804 – 6806
Angewandte
Chemie
trialkoxysilanes were seen in a new light
by Masfumui Unno (Gunma University,
Kiryu, Japan) and co-workers. They
succeeded in the synthesis of oligomeric
silsesquioxanes with control over the
stereochemistry.[9] Besides ladder-type
structures, cage-type silsesquioxane are
used as precursors for nanocomposites
in materials chemistry. For example,
Gion Calzaferri (University of Bern,
Switzerland) and his co-workers have
used R-H7Si8O12 to close channels of
dye-carrying zeolites and created new
photonic devices by this technique.[10]
The corners of cagelike silsesquioxanes
and spherosilicates can be functionalized through various methods by
organic groups. Such molecular building
blocks are used by Richard Laine (University of Michigan, Ann Abor, USA)
and his group to form three-dimensional
nanocomposites.[11]
The controlled formation of nanoparticles is also an important topic in the
field of silicon chemistry. Application of
novel types of surfactant molecules that
contain a citrate head group allowed
Michael Brook (McMaster University,
Hamilton, Canada) and co-workers to
prepare and stabilize silver nanoparticles. Self-organization of the derived
systems leads to chains and ellipsoidal
rings, as well as structures of higher
complexity, such as multilayer bands
(Figure 1). Solvent-based methods to
produce silicon nanoparticles and functionalize their surfaces in situ were
presented by Susan Kauzlarich (University of California, Davis, USA).[12, 13] The
particles thus obtained show a photoluminescence that is stable over long
periods of time.
Graham Showell (Paradigm Therapeutics Ltd., Cambridge, GB) impressively convinced the audience that organosilicon-based medicinal chemistry can
lead to the development of novel drugs.
Often this development is based on the
selection of proven compounds and the
formation of derivatives that contain
silicon atoms or silicon-containing
groups.
Sila
substitution
(C–Si
exchange) in well-known drugs—the
formation of so-called bioisosters—is
one possibility to search for novel compounds that reveal advantageous biological properties, such as improved
pharmacodynamic profiles. Furthermore, this approach can be used to get
Angew. Chem. Int. Ed. 2005, 44, 6804 – 6806
Figure 1. Novel surfactant molecules for the production of silver nanoparticles and their
supramolecular arrangements, as presented by Brook.
around existing patents and help to
minimize costs in pharmaceutical
research. Some fundamental differences
in the reactivity of silicon compared to
that of carbon can also lead to changes
in the biological properties of the silicon-containing analogues, and the
advantageous differences are exploited
in the design of novel pharmaceuticals.[14]
Iain MacKinnon (Dow Corning
Ltd., Barry, GB) presented to the predominately academic audience the
many industrial applications of functionalized polysiloxanes. He showed industrial solutions for the large-scale production of N-functionalized polysiloxanes, which are used in everyday products such as shampoos, shoe polish, or
conditioners. The introduction of
organic functional groups to avoid the
yellowing of the N-functionalized polysiloxanes was one of the many examples
discussed.
The functionalization of silicon surfaces is an important aspect in many
applications as well as being of fundamental chemical interest. Jillian Buriak
(University of Alberta, Edmonton,
Canada) revealed a selection of chemical reactions at surfaces that differ
fundamentally from the molecular
chemistry of silicon compounds. One of
the methods her group has used is
electrografting, which has allowed the
covalent attachment of alkynes to Hterminated silicon surfaces by conducting-probe atomic force microscopy (CPAFM). This method allowed the production of structures with dimensions of
less than 30 nm (Figure 2).[15]
Manfred Sumper (University of
Regensburg, Germany) introduced the
audience to the world of biomineralization, where silicates and the biochemistry of silicon play an important role. The
complex and sometimes spectacular
shapes of diatoms are an interesting
display of Nature. Analysis of the silicate cell walls reveal that they are
formed by composites that contain zwitterionic proteins (silaffines) and long-
Figure 2. Application of CP-AFM makes it possible to connect molecules covalently on modified
silicon surfaces and to form patterns. Adapted from Reference [15].
2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
6805
Meeting Reviews
chain polyamines together with the
inorganic phase. Quaternized ammonium groups seem to play a particular role
in these systems.[16] The complex mechanisms of their patterning can be
explained by the self-organization processes of polyamines, which act as templates.
ISOS XIV showed how exciting and
full of innovation the research into a
single element can be, and we look
forward again to see how this field
develops until the next meeting.
[1] M. Kira, J. Organomet. Chem. 2004, 689,
4475.
[2] A. Y. Cheng, S. B. Clendenning, G.
Yang, Z.-H. Lu, C. M. Yip, I. Manners,
Chem. Commun. 2004, 780..
6806
www.angewandte.org
[3] W. Y. Chan, S. B. Clendenning, A.
Berenbaum, A. J. Lough, S. Aouba,
H. E. Ruda, I. Manners, J. Am. Chem.
Soc. 2005, 127, 1765..
[4] D. Zhou, Y. Kawakami, Macromolecules
2005, 38, 6902.
[5] A. C. Finnefrock, R. Ulrich, A. Du Chesne, C. C. Honeker, K. Schumacher,
K. K. Unger, S. M. Gruner, U. Wiesner,
Angew. Chem. 2001, 113, 1247; Angew.
Chem. Int. Ed. 2001, 40, 1208.
[6] M. Kamperman, C. B. W. Garcia, P. Du,
H. Ow, U. Wiesner, J. Am. Chem. Soc.
2004, 126, 14708.
[7] D. Brandhuber, V. Torma, C. Raab, H.
Peterlik, A. Kulak, N. H(sing, Chem.
Mater. 2005, 17, 4262.
[8] D. Brandhuber, H. Peterlik, N. H(sing,
J. Mater. Chem. 2005, 15, 3896.
[9] M. Unno, Y. Kawaguchi, Y. Kishimoto,
H. Matsumoto, J. Am. Chem. Soc. 2005,
2256.
2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
[10] G. Calzaferri, S. Huber, H. Maas, C.
Minkowski, Angew. Chem. 2003, 115,
3860; Angew. Chem. Int. Ed. 2003, 42,
3732.
[11] R. M. Laine, J. Mater. Chem. 2005, 15,
3725.
[12] R. K. Baldwin, K. A. Pettigrew, E.
Ratai, M. P. Augustine, S. M. Kauzlarich, Chem. Commun. 2002, 1822.
[13] J. Zou, R. K. Baldwin, K. A. Pettigrew,
S. M. Kauzlarich, Nano Lett. 2004, 4,
1181.
[14] G. A. Showell, J. S. Mills, Drug Discov.
Today 2003, 8, 551.
[15] P. T. Hurley, A. E. Ribbe, J. M. Buriak, J.
Am. Chem. Soc. 2003, 125, 11 334.
[16] S. Wenzl, R. Deutzmann, R. Hett, E.
Hochmuth, M. Sumper, Angew. Chem.
2004, 116, 6059; Angew. Chem. Int. Ed.
2004, 43, 5933.
DOI: 10.1002/anie.200503350
Angew. Chem. Int. Ed. 2005, 44, 6804 – 6806
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