The Catalyst Review - February 2015 - 17

EXPERIMENTAl
Radical Polymer
Approach...
A protocol for ring-opening metathesis
polymerization, or ROMP, that uses
organic initiators rather than transitionmetal
catalysts has been developed.
The new polymerization method could
be a boon to makers of polymers with
electronic or biological applications.
Today, polymer producers use ROMP to
make such materials as polynorbornene,
trade named Norsorex, which can be
used as a shock absorber and a high-grip
material, as well as for water filtration.
Polydicyclopentadiene, which is used
to make body parts for tractors and
construction equipment, is also made via
ROMP. But polymer makers have been
limited in their ability to expand their
offerings with ROMP because traces of
the transition metals used to initiate
polymerization can be left behind in the
product. That's a problem in electronic
applications, where the residual metals
affect the polymer's conductivity and
capacitance. It's also troublesome for
polymers with biological applications
because the metals used for ROMP are
toxic. With these limitations in mind,
University of Washington, Seattle,
chemists Andrew J. Boydston, Kelli A.
Ogawa, and Adam E. Goetz set out to
initiate a ROMP reaction without metals.
Instead, they used radical cations made
from one-electron oxidation of electronrich
vinyl ethers. The researchers think
the radical cation reacts with a double
bond to produce a cyclobutane radical
cation. If the double bond is part of a
small ring system, such as norbornene, the
ring's strain will prompt the cyclobutane
radical cation to open up, initiating the
polymerization process. Trial and error led
the chemists to photoredox chemistry as
the best method for creating the radical
cation initiator. So far, the researchers
have used only norbornene as a monomer
in metal-free ROMP, but Boydston says
they want to expand the scope of the
reaction. Source: Chemical & Engineering
News, 1/29/2015, p. 6.
Cheap And Abundant Chemical Outperforms
Precious Metals As A Catalyst...
A team of Caltech chemists has discovered a method for producing a group of siliconcontaining
organic chemicals without relying on expensive precious metal catalysts.
Instead, the new technique uses as a catalyst a cheap, abundant chemical that is
commonly found in chemistry labs around the world-potassium tert-butoxide-to
help create a host of products ranging from new medicines to advanced materials.
And it turns out that the potassium salt is more effective than state-of-the-art precious
metal complexes at running very challenging chemical reactions. "We have shown
for the first time that you can efficiently make carbon-silicon bonds with a safe and
inexpensive catalyst based on potassium rather than ultrarare precious metals like
platinum, palladium, and iridium," says Anton Toutov, a graduate student working
in the laboratory of Bob Grubbs, Caltech's Victor and
Elizabeth Atkins Professor of Chemistry. "We're very
excited because this new method is not only 'greener'
and more efficient, but it is also thousands of times
less expensive than what's currently out there for
making useful chemical building blocks. This is a
technology that the chemical industry could readily
adopt." The finding marks one of the first cases in
which catalysis moves away from being a practice that
is fundamentally unsustainable. While the precious
metals in most catalysts are rare and could eventually
run out, potassium is an abundant element on Earth.
"To be able to do this type of reaction, which is one of
the most-studied problems in the world of chemistry,
with potassium tert-butoxide-a material that's not
precious-metal based but still catalytically active-was
a total shocker," says Coauthor Brian Stoltz, professor
of chemistry at Caltech. The current project got its start a couple of years ago when
coauthor Alexey Fedorov-then a postdoctoral scholar in the Grubbs lab (now at
ETH Zürich)-was working on a completely different problem. He was trying to break
carbon-oxygen bonds in biomass using simple silicon-containing compounds, metals,
and potassium tert-butoxide, which is a common additive. During that process, he ran
a control experiment-one without a metal catalyst-leaving only potassium tertbutoxide
as the reagent. Remarkably, the reaction still worked. And when Toutov-who
was working with Fedorov-analyzed the reaction further, he realized that in addition
to the expected products, the reaction was making small amounts of organosilanes.
This was unexpected since organosilanes are very challenging to produce. Bolstered
by the finding, Toutov refined the reaction so that it would create only a single
desired organosilane in high yield under mild conditions, with hydrogen gas as the
only byproduct. Then he expanded the scope of the reaction to produce industrially
useful chemicals such as molecules needed for new materials and derivatives of
pharmaceutical substances. So far, the chemists do not know why the simple catalyst
is able to drive these complex reactions. Toutov says that unlike some other catalysts
that stop working or become sensitive to air or water when scaled up from the singlegram
scale, this new catalyst seems to be robust enough to be used at large, industrial
scales. To demonstrate the industrial viability of the process, the Caltech team used
the method to synthesize nearly 150 grams of a valuable organosilane-the largest
amount of this chemical product that has been produced by a single catalytic reaction.
The reaction required no solvent, generated hydrogen gas as the only byproduct,
and proceeded at 45°C-the lowest reported temperature at which this reaction has
successfully run, to date. Source: PhysOrg online, 2/4/2015.
The Catalyst Review
February 2015
17

The Catalyst Review - February 2015

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