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Crosslinking in Molecular Main Group Element Chemistry.

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Meeting Reviews
Crosslinking in Molecular
Main Group Element Chemistry**
Rainer Streubel
O
ver the last forty to fifty years,
important research areas of molecular
main-group-element chemistry have
been driven apart by focusing (too
much) on themselves and have thereby
missed benefiting interactions. These
areas involve the study of neutral and
ionic species such as compounds with
high- and/or low-coordinated centers,
reactive intermediates, transition-metalstabilized unusual molecules, novel
heterocycles, and last, but not least,
applications in various fields of homogeneous catalysis, hybrid and/or inorganic polymers, functional molecules
(sensors, molecular magnets, OLEDs,
ionic liquids, etc.), and single-source
precursors for new materials. This fact,
together with the advance of more
elaborate computational methods and
programs that are able to tackle ever
more complicated problems and realsize large molecules, has increased
attention and created the wish to
merge these fields of molecular maingroup-element chemistry.
An initiative entitled “Innovative
Synthesis of Novel Main-Group Compounds and Its Application”, proposed
by a group of internationally renowned
scientists headed by Yohsuke Yamamato (University of Hiroshima, Japan)
who recognized this challenge in the
field, was approved by the Japan Society
for the Promotion of Science (JSPS)
[*] Prof. Dr. R. Streubel
Institut fr Anorganische Chemie
Rheinische Friedrich-Wilhelms-Universit#t
Bonn
Gerhard-Domagk-Strasse 1
53121 Bonn (Germany)
E-mail: r.streubel@uni-bonn.de
[**] Second Core-to-Core Symposium on Main
Group Element Chemistry, August 26–28,
2006, University of Tokyo.
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within the Core-to-Core Program—this
initiative represents the only proposal
on fundamental research in chemistry.
The center of this network is in Japan,
and it has two other main contributing
countries: United States and Germany.
Each has a national coordinator (Y.
Yamamoto/Japan, A. J. Arduengo/
USA, K. Seppelt/Germany) and additional cooperative members in these
countries as well as others such as
Canada, France, Switzerland, the Netherlands, New Zealand, UK, and Finland,
thus altogether connecting 26 research
teams outside Japan.
According to this background and
the principal ideas outlined above, the
Second Core-to-Core Symposium comprised single sessions each day with a
total of 24 plenary lectures, nine short
lectures, and a poster session (49 contributions). The opening lecture entitled
“The Strongest (yet Gentlest) Acid” was
given by C. A. Reed (Riverside, USA),
who demonstrated the versatile applicability of H(CHB11Cl11), for example,
for the protonation of C60, C6H6, or
R3Si+ ions, by virtue of the inertness of
the corresponding anion. J. G. Verkade
(Iowa, USA) presented long-awaited
applications, following many years of
fundamental research, of azaphosphatranes in various fields of organocatalysis, such as C C and C N coupling
reactions.
K. Lammertsma (Amsterdam, The
Netherlands) reported on novel functionality in organophosphorus chemistry
and showed the importance of nucleophilic and electrophilic terminal phosphinidene complexes, the latter of which
are especially useful in P,C-heterocyclic
chemistry. D. A. Dixon (Tuscaloosa,
USA) explained and illustrated new
advances in computational main-group
chemistry by predicting, for example,
(CF3SO2)3CH as a promising new superacid. H.-J. Gr?tzmacher (Z?rich, Switzerland) showed how to make the true
(monocoordinated and anionic) “CP”
(cyaphide) ligand by using C Si bond
cleavage of a Ru-coordinated silyl-sub-
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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stituted phosphaalkyne, thus opening a
new avenue in coordination chemistry.
Three short lectures gave insights
into recent advances in experimental
and theoretical areas: M. Yoshifuji
(Tuscaloosa, USA) showed that the
chemistry of 1,3-diphosphacyclobutane2,4-diyls, which are fascinating heterocyclic singlet diradicaloids (first
reported by E. Niecke in 1995), gives
access to new heterocyclic radical cations. M. Ochiai (Tokushima, Japan)
discussed hypervalent alkynyl- and
alkenyl(aryl)-l3-bromanes and their
broad applications in organic synthesis.
S. Nagase (Okazaki, Japan) reported on
the effects of bulky groups on the triple
bonding in REER (R = alkyl; E = Si,
Ge, Sn) compounds and the short distance in Na2[RGaGaR]“, thus convincingly demonstrating current computing
abilities and their utility in the understanding of structure and bonding. The
last lecture of the first day was given by
F. Mathey (Riverside, USA), who described the way from 2H-phospholes to
phosphaporphyrins, which illustrated
again how long it can take to make use
of once curious findings, such as the 1H-/
2H-phosphole rearrangement.
The second day started with a lecture by D. Lentz (Berlin, Germany) on
the synthesis and structure determination of tellurium(IV) compounds, in
which he described cyanide and mixed
fluoride/cyanide species of tellurium
and showed the structural influence of
solvates. J. Escudie (Toulouse, France)
illustrated the synthetic pathways necessary to access heteroallenes containing low-coordinated heavy elements of
Groups 14 and 15 and their use in
heterocyclic chemistry. R. RHau
(Rennes, France) demonstrated how
new OLED materials can be designed
based on fundamental knowledge of
organophosphorus p-conjugated systems that comprise phospholes as a
central building block. R. Streubel
(Bonn, Germany) described new syntheses and bond-selective ring-expansions of oxaphosphirane complexes, thus
Angew. Chem. Int. Ed. 2006, 45, 6418 – 6419
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presenting therein the first reactions of
these epoxide analogues in phosphorus
heterocyclic chemistry. F. P. Gabbai
(College Station, USA) discussed polyfunctional and cationic boranes, focusing on their reduction chemistry and
anion complexation, and also described
novel boron-containing radicals.
A special minisymposium comprising eight lectures was integrated to
celebrate the 70th birthday of Kin-ya
Akiba. The opening short lecture of this
minisymposium was given by the chairman Y. Yamamoto with a short report
entitled “Hypervalent Chemistry: From
Bond Switching to Penta- and Hexacoordinate Carbon Compounds” that discussed the most recent results from a
collaboration with C. A. Reed on the
use of weakly coordinating anions. K.
Seppelt (Berlin, Germany) described
reactions of the organoselenonium (telluronium) cation in his plenary lecture,
which also discussed the first synthesis
of tellurirenium ions. A stimulating
short talk was given by K. Tamao
(Saitama, Japan), who showed how
organoelemental chemistry can be
directed towards material science as
exemplified by the chemistry of siloles.
The lecture by M. Mikolajczyk (ŁKdź,
Poland) was more devoted to “pure”
organic synthesis, with a demonstration
of how a-phosphorylvinyl sulfoxides can
be successfully employed in asymmetric
synthesis. The topic of the lecture by N.
Tokitoh (Kyoto, Japan) was how to
obtain various forms of kinetically stabilized tin–carbon double-bond systems.
A highlight of this short talk was discussion of a 2-stanna-naphthalene derivative. “Going supramolecular” was the
motto of W.-W. du Mont (Braunschweig, Germany), who used unusual
soft–soft interactions to build up
extended networks based on triisopropylphosphane selenide and telluride
ligands. How to gain access to photocontrollable properties and reactivities
of Si and P compounds was discussed by
T. Kawashima (Tokyo, Japan). The final
contribution in this session was a ple-
Angew. Chem. Int. Ed. 2006, 45, 6418 – 6419
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nary lecture that could have been entitled “The Music Plays in the Ligand”
delivered by A. J. Arduengo (Tuscaloosa, USA), who explained how Nheterocyclic carbenes can be tuned and
used to realize unusual valence states of
carbon and other main-group elements.
The final day of this marathon of
excellence was opened by L. J. Wright
(Auckland, New Zealand), who presented results in the area of metallabenzenoids that (again) probed the understanding of aromaticity. I. Manners
(Bristol, UK) gave insights into catalytic
routes to rings, chains, and macromolecules based on inorganic elements, thus
illustrating the progress in this field
towards applications. More fundamentally oriented was the plenary lecture by
R. Laitinen (Oulu, Finland), who
focused on recent progress in imidoselenium and –tellurium chemistry as the
“partly forgotten relatives” of sulfurimides.
The subsequent three lectures built
bridges between common and highly
unusual main-group ligand chemistry
and showed their impact in transitionmetal chemistry. P. W. Roesky (Berlin,
Germany) started with bis(diphosphanylamides) and moved on to discuss [h5C5Me5Al] as a ligand system. F. E. Hahn
(M?nster, Germany) continued by
describing a tetracarbene ligand with
crown ether topology. M. Kira (Sendai,
Japan) focused on transition-metal complexes of disilenes and digermenes and
their reactions, such as ligand exchange
and cycloaddition with phenylacetylene.
A. Sekiguchi (Tsukuba, Japan) described the reactivity of stable disilyene
compounds towards organic nucleophiles and various p systems. The bonding in heavier Group 14 element alkynes
was impressively explained by P. P.
Power (Davies, USA), who revealed
how tiny changes in the ligands of
REER (R = alkyl; E = Si, Ge, Sn, Pb)
might result in surprising structural
changes and bring some unexpected
chemistry to the fore, such as spontaneous reaction of a GeII species with
elemental hydrogen at ambient temperature! M. Driess (Berlin, Germany)
focused the attention on heterofulvenelike silylenes and germylenes with
ambivalent reactivity, thus also leading
to the first intramolecular donor-stabilized silaformamide. The final speaker
of the session and symposium was D.
Tilley (Berkeley, USA), who reported
on bond activations and catalytic transformations involving transition-metal–
silicon systems in his plenary lecture,
which demonstrated that substrate activation is not necessarily and intimately
intertwined with metals (or metal centers).
In summary, this scientific meeting
was truly at the frontiers of research in
molecular main-group chemistry (centered around Group 14 and 15 elements) and very inspiring in fields such
as unusual open-shell systems, novel
low-valent compounds, and organoelemental catalysis including hydrogen
activation (and maybe storage in the
future). The meeting was perfectly
suited to create and/or strengthen
research
networks
internationally.
There was also something special in
the air besides chemistry, including
enjoyable cultural efforts such as the
exchange of scientific Haikus (a Japanese lyric verse form with three
unrhymed lines of five, seven, and five
syllables that traditionally invokes an
aspect of nature or the seasons).
Tell your dream to flasks,
pour your love to reagents,
and I believe individual persons are
most important.
(Kin-ya Akiba, 1980;
translated by Y. Yamamoto, 2006)
Bonds break, atoms fly,
elemental arrays inspire.
Glimpses of the future.
(Don Tilley, 2006)
DOI: 10.1002/anie.200603708
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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