The synthesis and characterization of a {CuNO}10 complex namely, [Cu(NO)(CH3NO2)5][PF6] 2 has been achieved by addition of two equiv of [NO][PF6] to a suspension of copper powder in nitromethane. In the solid-state, this complex features a bent Cu--N--O moiety [121.0(3)o] and a long Cu-N bond distance. The electronic description of these compound is best described as a Cu(II) center interacting with an NO radical ligand. However, this complex readily reacts with methylated benzenes to form [arene, NO][PF6] and [Cu(arene)2][PF6].

The nickel nitrosyl complex namely, [Ni(NO)(CH3NO2) 3][PF6] is synthesized by treatment of nickel powder in nitromethane with [NO][PF6] in the presence of NiI2 catalyst. This complex has an Enemark-Feltham configuration of {NiNO}10. It exhibits a tetrahedral geometry about the Ni center with a linear Ni--N--O bond angle [174.1(8)o]. The nitromethane ligands are readily substituted with a number of different donor ligands, such as acetonitrile, mesitylene, and 2,2-bipyridine (bipy).

Addition of bipy to [Ni(NO)(bipy)][PF6] results in formation of a rare five-coordinate nickel nitrosyl complex [Ni(NO)(bipy)2][PF 6]. This complex exhibits a bent reduced NO- ligand in the solid state. On standing in dichloromethane solution N2O is evolved. Conversely, on standing in acetonitrile the NO coupled product (bipy)Ni(kappa 2-O2N2) precipitates from solution. Addition of acetylacetone to [Ni(NO)(bipy)2][PF6] yields clean formation of [Ni(acac)(bipy)2][PF6], N2O and H2O.

The reaction mechanism of NO reduction was studied by performing a number of control studies. The complex [Ni(NO)(bipy)(Me2phen)][PF6], which contains sterically bulky methyl groups, does not yield N2O over 24 hours, supporting a bimetallic coupling pathway. In contrast, addition of 1 equiv of NO gas to [Ni(NO)(bipy)(Me2phen)][PF6] results in the isolation of the NO disproportionation product. Reaction of [Ni(NO)(bipy)][PF6] with AgPF6 or [NO][PF6] in MeCN, in the presence of 2 equiv bipy, results in formation of [Ni(bipy) 3][PF6]2 and release of NO gas in moderate yields.

Addition of the inner sphere oxidant Ph2S2 does not yield denitrosylation, but the diphenyldisulfide adduct [{(bipy)(NO)Ni} 2(&mgr;-S2Ph2)][PF6]2 is formed in good yield. However, tetramethylpiperidine-1-oxyl (TEMPO) does result in cleavage of the Ni--NO bond and generation of NO gas. The metal containing product is [(bipy)Ni(&eegr;2-TEMPO)][PF6]. Finally, pyridine-N-oxide forms the adduct complex, [Ni(NO)(bipy)(ONC5H 5)][PF6].