such as "Introduction", "Conclusion"..etc
RIVERSIDE, Calif. -- Aug. 18, 2005 -- Chemists at the University of
California, Riverside have synthesized a new class of carbenes --
molecules that have unusual carbon atoms -- that is expected to have
wide applications in the pharmaceutical industry, ultimately resulting
in a reduction in the price of drugs.
Called cyclic alkyl amino carbenes or CAACs, the molecules attach
themselves to metals, such as palladium, to form highly efficient
catalysts that allow chemical transformations otherwise considered
impossible. The carbenes modulate the properties of the metals to which
they are bound and can facilitate and speed up reactions involving
Study results appear in the Angewandte Chemie International Edition, and were published online Aug. 1.
A carbene is a molecule that has a carbon atom with six
electrons instead of the usual eight. Because of the electron
deficiency, carbenes are highly reactive and usually unstable in
In their paper, the UCR chemists discuss a set of chemical
reactions involving the use of catalysts other than those that are
CAAC-based. The authors note that these catalysts need strong heating
to be effective. They add that the CAAC-based catalysts, on the other
hand, can be used not only at room temperature but also in smaller
amounts than is necessary for the other catalysts.
"For more than a century, most catalysts were prepared using
chemical compounds called phosphines," said Guy Bertrand, the lead
author of the study and Distinguished Professor of chemistry. "But in
the 1990s, carbenes were found to be useful to make catalysts. The new
carbenes we have prepared in the laboratory are such that they protect
the metals to which they bind, making the metal catalysts more stable
and longer lasting."
Because nitrogen atoms stabilize a carbene when they are
adjacent to it, chemists believed until now that two nitrogen atoms
were necessary in a carbene to make efficient catalysts. But having two
nitrogen atoms also imposes structural limitations at the center of the
The carbenes synthesized by the UCR chemists has only one
nitrogen atom, which lends the molecule a far more flexible structure.
In effect, the carbenes are bigger at the metallic center of the
catalyst, a feature that improves the efficiency of the catalyst.
"We started this project nearly two years ago," said Vincent
Lavallo, an undergraduate researcher in Bertrand's laboratory and the
first author of the paper. "The carbene-based catalysts we report can
simplify complex chemical preparations. Further, just mild temperatures
are needed for the catalyst to be effective. Because of the catalyst's
longevity, you need only a small amount to achieve your final product.
All of this can dramatically reduce the cost of manufacturing drugs,
given that pharmaceutical companies are increasingly using
carbene-supported catalysts for their chemical reactions."
Bertrand's research group plans to continue to modify the new
carbenes to find more efficient catalysts. "We're looking also for new
catalytic reactions facilitated by these new carbene metal complexes,"
Lavallo said. "The CAACs have made the field of carbene chemistry more
exciting than ever."
Yves Canac, Carsten Pr--sang and Bruno Donnadieu of UCR
assisted with the study. The National Institutes of Health and the
chemicals manufacturer Rhodia provided support.
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