Scientists in France have developed the first mild, enzyme-inspired method to convert methane to industrially valuable products.

AlexanderSorokin and colleagues at the University of Lyon made an organometalliccomplex that oxidises methane to methanol at low temperatures usinghydrogen peroxide.
Methane is the main component of natural gasbut also the least reactive. In the human body, the enzyme methanemonooxygenase converts methane to methanol under very mild conditions.Essential for its activity is its diiron centre, which forms a reactiveoxygen-bridged species that can oxidise C-H bonds. Chemists have triedto mimic this catalytic process but until now have not succeeded.
Usingporphyrin-like ligands known as phthalocyanines, Sorokin made a diironcomplex in which the two irons are bridged with a nitrogen atom. Hefound that the complex activated hydrogen peroxide, forming a verystrong species that oxidised methane in water at temperatures as low as25 degrees Celsius. Depending on the reaction conditions, the resultingmethanol could be oxidised further to formaldehyde and formic acid.
"This is a significant step in advancing one of the great problems: the direct partial oxidation of methane to methanol"
- Robert Crabtree, Yale University, New Haven, US
'Dimericstructures are often considered as inactive in catalysis,' explainsSorokin. 'However, we hypothesised that diiron porphyrin-like complexescould stabilise high oxidation state species due to delocalisation ofcharge at the two irons and the ligands. The key point is the stabilityof the binuclear core during catalysis.'Robert Crabtree, professorof inorganic chemistry at Yale University, New Haven, US, is impressedby the results. 'This is a significant step in advancing one of thegreat problems: the direct partial oxidation of methane to methanol,'he says.
Sorokin says he believes that this novel catalystpresents great potential for further development. 'This finding shouldinitiate studies directed towards optimising its structure to tune itscatalytic properties and increase its scope towards the clean oxidationof other difficult-to-oxidise substrates to useful products,' he says.
Roxane Owen


Link to journal articleBio-inspired oxidation of methane in water catalyzed by N-bridged diiron phthalocyanine complex
Alexander B. Sorokin, Evgeny V. Kudrik and Denis Bouchu, Chem. Commun., 2008
DOI: 10.1039/b804405h