Researchers at the University
of California, Riverside have successfully created in the
laboratory a class of carbenes, highly reactive molecules, used to make
catalysts—substances that facilitate chemical reactions. Until now, chemists
believed these carbenes, called “abnormal N-heterocyclic carbenes” or aNHCs,
were impossible to make.
Carbenes are made up of unusual carbon atoms and are usually
unstable in nature. They attach themselves to metals to form metal-carbene
complexes that serve as efficient catalysts used widely in the pharmaceutical
industry.
Molecular structure of the C5-Abnormal N-Heterocyclic Carbene (blue: nitrogen atoms; violet: abnormal carbene carbon atom; gray: normal carbon atoms). Image credit: Bertrand lab, UC Riverside.
The metal-carbene complexes are formed in two ways: (a) the
complex is created in one step, without first preparing carbene independently,
and (b) a metal and an independent carbene are brought together to make the
complex.
Most often the metal used in a metal-carbene complex is
rhodium, gold, platinum or palladium—all of which are very expensive and, in
some cases, even toxic. To bring down the cost of catalysts, when possible,
carbenes are used independently (without metals) in many chemical reactions.
Until now, aNHCs have been used as only metal-carbene
complexes, never independently. Chemists had assumed that aNHCs cannot exist
freely, which made them impossible to make.
Now UC Riverside’s Guy
Bertrand, a distinguished professor of chemistry, and colleagues have
challenged that assumption by successfully creating aNHCs that are metal-free
and can be used to make any desired complex.
“Many chemical species are believed to be unstable because
they do not obey the rules we learned at school, and consequently nobody tries
to make them,” said Bertrand, who led the research project. “The role of
scientists, however, is to challenge former hypotheses. That is just what we
did in the case of the aNHCs, and we were successful.
“The aNHCs are stable at room temperature both in the solid
state and in solution, which means their application as metal-free catalysts is
extremely wide, greatly benefiting industry by making possible scores of new
chemical reactions.”
Results of the study appear in the Oct. 23 issue of Science.
“This study, reporting the synthesis and characterization of
an entirely different class of metal-free NHCs, could open new horizons and
have a huge impact on the field of catalysis,” said John Schwab, who oversees
organic synthesis grants at the National Institutes of Health’s National
Institute of General Medical Sciences. “The potential applications to drug
discovery and manufacture are exciting, since catalytic processes can help keep
costs in check and be environmentally friendly, to boot.”
Bertrand is interested in making aNHCs commercially
available. “We hope many chemists in the world will use these carbenes and find
some new applications,” he said.
The UCR Office
of Technology Commercialization has filed a patent application on the
technology and is currently seeking partners in industry interested in
developing the technology commercially.
The research project was funded by the National Institutes
of Health. The National Council for Science and Technology (CONACYT), Mexico,
provided Aldeco-Perez, the first author of the research paper, with financial
support.
Study abstract
Original
article
