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

Alexander Sorokin and colleagues at the University of Lyon made an organometallic complex that oxidises methane to methanol at low temperatures using hydrogen peroxide.

Methane is the main component of natural gas but also the least reactive. In certain types of bacteria, the enzyme methane monooxygenase converts methane to methanol under very mild conditions. Essential for its activity is its diiron centre, which forms a reactive oxygen-bridged species that can oxidise C-H bonds. Chemists have tried to mimic this catalytic process but until now have not succeeded.

Using porphyrin-like ligands known as phthalocyanines, Sorokin made a diiron complex in which the two irons are bridged with a nitrogen atom. He found that the complex activated hydrogen peroxide, forming a very strong species that oxidised methane in water at temperatures as low as 25 degrees Celsius. Depending on the reaction conditions, the resulting methanol could be oxidised further to formaldehyde and formic acid.

'Dimeric structures are often considered as inactive in catalysis,' explains Sorokin. 'However, we hypothesised that diiron porphyrin-like complexes could stabilise high oxidation state species due to delocalisation of charge at the two irons and the ligands. The key point is the stability of the binuclear core during catalysis.'

Robert Crabtree, professor of inorganic chemistry at Yale University, New Haven, US, is impressed by the results. 'This is a significant step in advancing one of the great problems: the direct partial oxidation of methane to methanol,' he says.

Sorokin says he believes that this novel catalyst presents great potential for further development. 'This finding should initiate studies directed towards optimising its structure to tune its catalytic properties and increase its scope towards the clean oxidation of other difficult-to-oxidise substrates to useful products,' he says.

Roxane Owen