Rare metal complex of nitrous oxide, stable even at room temperature

Used as an essential pain relief medicine, an oxidant injected into racing engines and an aerosol propellant, N2O is undeniably valuable to humans. It’s also a harmful greenhouse gas resulting primarily from agricultural activities. Although present in much smaller concentrations in the atmosphere than CO2, N2O is 300 times more effective in trapping heat than CO2 is, making it a dangerous contributor to climate change. This has led scientists to research ways of limiting N2O emissions and to investigate the compound’s catalytic decomposition with metals.

A recent study supported by the EU-funded SMAC-MC project has now shown that N2O can bind to metals in a similar way to CO2, forming comparable or stronger bonds than CO2 does. This ability opens the way for N2O use in synthetic chemistry and for its degradation into substances that don’t harm the atmosphere. The study was published in the scientific journal ‘Angewandte Chemie International Edition’.

The natural process of converting N2O into N2 and water can be mimicked in labs using catalytic metal complexes. However, unlike CO2, well-defined complexes of N2O with transition metals are rare. This could be because N2O is a poor ligand (a molecule that bonds to a metal atom or ion) when compared to CO2. In order to figure out how and why, the research team synthesised comparable metal complexes of N2O and CO2 and studied the metal-ligand interaction.The results of the study were unexpected. The researchers showed that N2O’s ability to bind to metal is in fact as good as or even better than that of CO2. “It appears that the oxidizing character of N2O is mostly, if not entirely, responsible for the scarcity of metal complexes employing this ligand,” reported co-author and SMAC-MC lead researcher Prof. Heikki M. Tuononen of the University of Jyväskylä in a news release posted on the ‘EurekAlert!’ website. “Once we had the right metal partner for N2O, their binding was strong enough that a rare side-on bound complex could be isolated and characterized even at room temperature,” explained co-author Dr Chris Gendy of the University of Jyväskylä in the same news item.

The research work shows that the design of more stable N2O complexes is possible and paves the way for the use of N2O in synthetic chemistry. “N2O is in many ways a great oxidant. It is thermodynamically strong, relatively cheap, and gives N2 as the only side product,” observed Prof. Tuononen. Co-author Prof. Roland Roesler of the University of Calgary added: “It would certainly be great to see more widespread use of N2O as an oxidant in metal-catalysed reactions. At the same time, we should not forget the role it plays in the atmosphere.”

“Nature has found elegant enzymatic pathways to convert N2O into products that are harmless to the atmosphere. We should aim for the same with our manmade emissions using novel catalysts,” the researchers concluded in the same news release. The team’s achievements are furthering the SMAC-MC (Small Molecule Activation by Main-Group Compounds) project’s goal of promoting breakthroughs in the design of novel compounds based on main group elements for the activation of small molecules.

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SMAC-MC project