Using large molecules to break nitrogen bonds.

Using large molecules to break nitrogen bonds.

A new way to split the strong nitrogen-nitrogen bond without the usual high-temperature and high-pressure conditions of the Haber-Bosch process could ease the task of incorporating atmospheric nitrogen into ammonia, pharmaceuticals, dyes, explosives and other products.

Paul Chirik and his colleagues from Cornell University, US, claim to have devised a way to split nitrogen molecules under milder conditions within liquids, a step that may lead to a variety of energy-efficient techniques for creating nitrogen-bearing substances.

The key to the new reaction is the synthesis of a permethylated cyclopentadienyl, a molecule so large it can attach to only one end of a nitrogen molecule.

Chirik and his colleagues found that removing one methyl group from each ring created a complex that was just the right size to snuggle up to both atoms in a nitrogen molecule and give an electron to each atom.This double donation, which can take place in an organic solvent at 100 °C and at atmospheric pressure, disrupts the triple bond between the nitrogen atoms. Further reactions in the same solution then finish the job of splitting the nitrogen molecules and adding hydrogen atoms to make ammonia.

The new, liquid-based technique may enable researchers to develop energy-efficient methods for making nitrogen-containing ingredients for pharmaceutical products, dyes, and other industrial chemicals.

Chirik has also been exploring a series of rhodium compounds that selectively break carbon-carbon bonds in common organic molecules.These reactions eventually could provide a new set of tools for the synthetic chemist.

Hamish Kidd