Mechanistic Insights into the Formation of N2O by a Nickel Nitrosyl Complex

Abstract

Reaction of [Ni(NO)(bipy)(Me2phen)][PF6] with 1 equiv of nitric oxide (NO) in CH2Cl2 results in the formation of N2O and [{(Me2phen)Ni(NO)}2(μ-η(1)-N:η(1)-O)-NO2)][PF6] (3), along with the known complex, [Ni(bipy)3][PF6]2 (4). The isolation of complex 3, which contains a nitrite ligand, demonstrates that the reaction of [Ni(NO)(bipy)(Me2phen)][PF6] with exogenous NO results in NO disproportionation and not NO reduction. Complex 3 could also be accessed by reaction of [Ni(NO)(Me2phen)][PF6] (5) with (Me2phen)Ni(NO)(NO2) (7) in good yield. Complexes 3, 5, and 7 were fully characterized, including analysis by X-ray crystallography in the case of 3 and 7. Furthermore, addition of 0.5 equiv of bipy to [Ni(NO)(bipy)][PF6] results in formation of the hyponitrite complex, [{(bipy)Ni(κ(2)-O2N2)}η(1):η(1)-N,N-{Ni(NO)(bipy)}2][PF6]2 (9), in modest yield. Importantly, the hyponitrite ligand in 9 is thought to form via coupling of two NO(-) ligands and not by coupling of a nucleophilic nitrosyl ligand (NO(-)) with an electrophilic nitrosyl ligand (NO(+)). X-ray crystallography reveals that complex 9 features a new binding mode of the cis-hyponitrite ligand.