Converting Nitrogen to a More Useful Form

Jan 09, 2007

Nitrogen-containing organic compounds are important products as well as intermediates for many pharmaceuticals, agrochemicals, and chemicals used in electronics. Air contains plenty of nitrogen, but it is in a form that cannot be used for chemical syntheses: nitrogen gas, a molecule made of two nitrogen atoms, is highly inert.

The main source of nitrogen today involves a detour by way of synthetic ammonia, a process requiring a lot of energy and explosive hydrogen gas under harsh conditions. In order to find synthetic pathways that do not rely on ammonia, scientists are searching for ways to fix atmospheric nitrogen in the form of higher-value organic compounds.

Chemists working with Paul J. Chirik at Cornell University (Ithaca, New York) have now found an interesting new method, which they describe in the journal Angewandte Chemie: they have bound nitrogen to carbon dioxide while maintaining the nitrogen–nitrogen bond, forming a hydrazine derivative. The metal hafnium promotes this reaction.

The two nitrogen atoms in a nitrogen molecule are so happy with each other that they have little incentive to enter into chemical bonds with other atoms. Direct formation of a bond between carbon and nitrogen, a requirement for the formation of organonitrogen compounds without resorting to ammonia, is a serious challenge for scientists. The nitrogen has to be “outsmarted”.

While it does not easily enter into chemical bonds with organic substances, molecular nitrogen does have a tendency to form coordination complexes by binding to a metal. When the nitrogen acts as ligand in these complexes, it receives electrons from the metal atom disrupting the strong nitrogen-to-nitrogen triple bond. Chemists often refer to this process as “activating” the nitrogen ligand, as new chemistry is now possible.

Chirik and his co-workers found out that the nitrogen gets activated just right in a hafnocene complex (whose hafnium atoms each have two aromatic five-membered carbon rings as additional ligands), in which the nitrogen molecule is grabbed side-on by two hafnium atoms. Carbon dioxide can then react with the activated nitrogen molecule.

Two carbon dioxide molecules push their way in between the nitrogen and the hafnium. One of the two nitrogen atoms thus forms two strong new bonds to two carbon atoms from the carbon dioxide. One of the nitrogen–nitrogen bonds remains intact. By using an organosilicon compound, the cores of the hafnocene complexes can be released—in the form of a silicon-containing organic hydrazine derivative.

Citation: Paul J. Chirik, Nitrogen–Carbon Bond Formation from N2 and CO2 Promoted by a Hafnocene Dinitrogen Complex Gives Access to a Substituted Hydrazine, Angewandte Chemie International Edition, doi: 10.1002/anie.200604099

Source: Angewandte Chemie

Explore further: A refined approach to proteins at low resolution

add to favorites email to friend print save as pdf

Related Stories

Cornell theorists continue the search for supersymmetry

20 minutes ago

(Phys.org) —It was a breakthrough with profound implications for the world as we know it: the Higgs boson, the elementary particle that gives all other particles their mass, discovered at the Large Hadron ...

Global wild tiger population to be counted by 2016

10 minutes ago

Thirteen countries with wild tiger populations agreed Tuesday to take part in a global count to establish how many of the critically endangered animals are left and improve policies to protect them.

Will tomorrow's robots move like snakes?

30 minutes ago

Over the last few years, researchers at MIT's Computer Science and Artificial Intelligence Lab (CSAIL) have developed biologically inspired robots designed to fly like falcons, perch like pigeons, and swim ...

Recommended for you

A refined approach to proteins at low resolution

2 hours ago

Membrane proteins and large protein complexes are notoriously difficult to study with X-ray crystallography, not least because they are often very difficult, if not impossible, to crystallize, but also because ...

Base-pairing protects DNA from UV damage

5 hours ago

Ludwig Maximilian University of Munich researchers have discovered a further function of the base-pairing that holds the two strands of the DNA double helix together: it plays a crucial role in protecting ...

Smartgels are thicker than water

5 hours ago

Transforming substances from liquids into gels plays an important role across many industries, including cosmetics, medicine, and energy. But the transformation process, called gelation, where manufacturers ...

Separation of para and ortho water

Sep 18, 2014

(Phys.org) —Not all water is equal—at least not at the molecular level. There are two versions of the water molecule, para and ortho water, in which the spin states of the hydrogen nuclei are different. ...

User comments : 0