Clever way to break the nitrogen-nitrogen bond

New reaction cleaves dinitrogen, brings carbon and nitrogen together

1:01pm, December 13, 2010
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To break some chemical bonds you need to know a guy, who knows a guy who knows a compound. Scientists ordered just such a hit and have broken two of the toughest bonds in chemistry in the laboratory equivalent of broad daylight. The reaction yields a new chemical connection and could lead to more direct routes for making various drugs or other biologically important compounds.

In the new work, a metal complex and carbon monoxide conspire to cleave the triple bond that connects two nitrogen atoms, one of nature’s strongest chemical bonds. Busting apart bonded nitrogen has always been a daunting task. Even when accomplished, it hasn’t necessarily yielded useful products.

The new reaction yields compounds with carbon-nitrogen bonds and proceeds at mild-mannered temperatures and pressures, the researchers report December 13 in Nature Chemistry. The reaction avoids the costly chemical detour of having to make ammonia (nitrogen and hydrogen) in order to achieve the useful carbon-nitrogen bond.

“This is an important contribution,” says MIT’s Christopher Cummins, who was not involved with the work. “We can add it to our chemical toolbox.”

About 78 percent of the Earth’s atmosphere is nitrogen, but harnessing it isn’t easy. Atmospheric nitrogen atoms live like inseparable twins, in the form of N2, strongly linked by a triple bond and relatively inert. This dinitrogen will react with oxygen and rain to Earth, where various microbes “fix” it — separate the twins, making them available to bond with other molecules, such as carbon.

To get that carbon-nitrogen bond in the lab, Cornell University chemist Paul Chirik and colleagues attacked the N2 bond with metal and carbon monoxide. The scientists started with a complex of the metal hafnium and dinitrogen in solution and then added carbon monoxide gas. Electrons from the hafnium and carbon “rip the triple bond,” says Chirik. As part of the reaction, the carbon from the carbon monoxide then bonds to the nitrogen atoms, creating a useful carbon-nitrogen bond.

Making compounds, such as nylon, that need the carbon-nitrogen bond currently requires making ammonia along the way, Chirik says. The new method may offer an alternative. “It’s as if you are flying from New York to Miami and you have a layover in Chicago,” says Chirik. “We’re trying to come up with direct flights.”

Even though the chemistry yields the farm chemical oxamide, notes Chirik, it doesn’t do so in large enough quantities to be useful. And while the reaction frees nitrogen, it’s not efficient for making ammonia: The Haber–Bosch process already does the job well and is in widespread use.

But in many instances, he says, figuring out a way to skip the Haber-Bosch temperatures and pressure requirements and its associated energy demands would be a plus. And thinking about these reactions may lead to new chemistry for making pharmaceuticals and other biologically important compounds.

“Down the line,” says Cummins, “the hope is [such reactions] can be engineered into industrial processes.”

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