Credit: © 2009 ACS

Carbon dioxide and nitrous oxide are both greenhouse gases, and either trapping or exploiting them — CO2 as a source of carbon and N2O as a strong oxidant — is highly desirable. However, they are very stable, and nitrous oxide is also a poor ligand to the transition metals usually required to mediate its reactivity.

In recent studies, small molecules have been activated by frustrated Lewis pairs — systems in which sterically bulky substituents prevent the formation of an acid–base adduct — rather than metal ions. Now, a team led by Douglas Stephan at the University of Toronto have reacted1 nitrous oxide with a basic, sterically bulky phosphine and a borane species. Characterization of the resulting solid, in good agreement with theoretical calculations, revealed an adduct that comprises a N=N–O moiety located between the phosphorus and boron atoms.

In collaboration with Stefan Grimme, Gerhard Erker and colleagues from Münster University, the researchers have also used the frustrated Lewis pair to bind carbon dioxide2. Theoretical calculations suggested a concerted mechanism, with the synchronous formation of the P–C and O–B bonds. A similar carbonic acid derivative was also obtained when the phosphine and borane groups were attached through a two-carbon linker, and carbon dioxide could be released from both species.