Nitrosyl Linkage Isomers: NO Coupling to N<sub>2</sub>O at a Mononuclear Site

Linkage isomers of reduced metal-nitrosyl complexes serve as key species in nitric oxide (NO) reduction at monometallic sites to produce nitrous oxide (N<sub>2</sub>O), a potent greenhouse gas. While factors leading to extremely rare side-on nitrosyls are unclear, we describe a pair of nickel-nitrosyl linkage isomers through controlled tuning of noncovalent interactions between the nitrosyl ligands and differently encapsulated potassium cations. Furthermore, these reduced metal-nitrosyl species with N-centered spin density undergo radical coupling with free NO and provide a N–N coupled <i>cis</i>-hyponitrite intermediate whose protonation triggers the release of N<sub>2</sub>O. This report outlines a stepwise molecular mechanism of NO reduction to form N<sub>2</sub>O at a mononuclear metal site that provides insight into the related biological reduction of NO to N<sub>2</sub>O.