Novel Copper-Nitrosyl Complex Synthesized

In work that could help researchers better understand how nitrogen is converted into different forms on a worldwide scale, a group at the University of California, Santa Barbara, has synthesized and characterized a novel copper-nitrosyl complex (J. Am. Chem. Soc., DOI: 10.1021/ja105930b).

The complex incorporates a Cu(II)–NO^• center, the radical species that is believed to be a key intermediate in the reduction of NO₂^– to NO by the enzyme copper nitrite reductase. The enzyme is found in a variety of bacteria and plays a key role in the global nitrogen cycle.

Chemistry professor Trevor W. Hayton, graduate student Ashley M. Wright, and staff crystallographer Guang Wu prepared the new complex by adding NOPF₆ to copper metal powder in nitromethane. Analysis of crystals formed from the resulting deep purple solution showed that the product was a distorted octahedral copper complex with five CH₃NO₂ ligands and one NO ligand. The nitrosyl group is bound in a bent geometry. The Cu–N bond length of 1.955 Å is significantly longer than those of other Cu–NO complexes, indicating a weak Cu–NO interaction in the new complex, the group reports.

The nitromethane ligands don't precisely mimic the histidine and water ligands bound to copper in the enzyme. Nevertheless, the synthesis and characterization of the complex could provide insight into the detailed mechanism of action of copper nitrite reductase, as well as the mechanisms of other NO_x reductive processes promoted by copper centers, says William B. Tolman, a chemistry professor at the University of Minnesota.

In addition to their synthetic and structural work on the complex, Hayton and colleagues found that it can transfer the nitrosyl group, as NO⁺, to a variety of substituted benzene compounds. The group is continuing to characterize the electronic structure and reactivity of the complex, Hayton says.