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Chemists at UC Riverside now offer a possible
solution. A class of carbenes – molecules that have unusual, highly
reactive carbon atoms – can mimic, to some extent, the behavior of
metals, the chemists have found. Called cyclic alkyl amino carbenes or
CAACs, these organic molecules, the researchers report, could be used
to develop carbon-based systems for storing hydrogen.
In their experiments, the researchers found that
the CAACs can split hydrogen under extremely mild conditions, a
behavior that has long been seen in metals reacting with hydrogen.
"The mode of action of these organic molecules,
however, is totally different from that of metals," said Guy Bertrand,
a distinguished professor of chemistry who led the research. "Moreover,
the CAACs are able to split ammonia as well – an extremely difficult
task for metals."
Bertrand explained that such a splitting of ammonia,
under certain conditions, can pave the way for transforming abundant
and inexpensive ammonia into useful amino compounds used to make
pharmaceuticals and bulk industrial materials. "This is one of the top
challenges for the 21st century," he said.
According to the UCR research team, the
metal-mimicking carbenes offer another low-cost and low-toxicity
benefit: Scientists now may be able to use non-metallic catalysts for
a reaction, called "hydrogenation reaction," which plays a critical
role in the food, petrochemical and pharmaceutical industries.
In their study, the researchers exposed a solution
of CAACs to both gaseous hydrogen and liquid ammonia. "We used nuclear
magnetic resonance spectroscopy to analyze the products," said Guido
Frey, the first author of the research paper and a postdoctoral fellow,
supported by the Alexander von Humboldt Foundation, in Bertrand’s lab.
"And we used single crystal X-ray diffraction analysis to confirm the
structure of the products."
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
nature. |
