Metal Complex-mediated NO Disproportionation

Metal complex-mediated NO disproportionation is in fact a very common reaction type  

As reduction of NO formally occurs as part of (i.e. one-half of) the process and the chemistry involves interconversion of nitrogen oxide compounds, it is of considerable interest. Thus, we mention a few examples here. The area has been recently reviewed [54]. 

This disproportionation requires N-N couphng chemistry in order to form the N2O product. Two intermediates are generally considered as plausible precursors to this reaction and subsequent product formation [12]. In form I (below), the metal center and corresponding hgand framework accommodate a ds-dinitrosyl species. In II, a hyponitrite (or hyponitrous) intermediate forms by electrophilic attack of NO onto a previously generated M-NO complex. 

Following N-N coupling, the next step would be O-atom abstraction (by NO) to yield NO2 and N2O the NO2 produced often is captured by a reduced metal ion, leading to a metal-nitrite complex. 

In addition to the copper complexes mentioned here, nitrogen oxide disproportionation can be mediated by a variety of other metal complexes, including those of cobalt [161], iron [152, 162-164], rathenium [165-167], manganese [168], rhodium [169] and iridium [93]. 

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