posted on 2016-02-19, 17:22authored byAshley M. Wright, Homaira T. Zaman, Guang Wu, Trevor W. Hayton
Reaction of [Ni(NO)(bipy)][PF6] (2) with AgPF6 or [NO][PF6] in MeCN results in formation of [Ni(bipy)x(MeCN)y]2+ and release
of NO gas in moderate yields. In contrast, the addition of the inner
sphere oxidant Ph2S2 to 2 does
not result in denitrosylation. Instead, the diphenyldisulfide adduct
[{(bipy)(NO)Ni}2(μ-S2Ph2)][PF6]2 (3) is formed in good yield. However,
oxidation of 2 with 2,2,6,6-tetramethylpiperidine-1-oxyl
(TEMPO) does results in cleavage of the Ni–NO bond and generation
of NO. The metal-containing product, [(bipy)Ni(η2-TEMPO)][PF6] (4), can be isolated as an
orange-brown solid in excellent yields. In the solid state, complex 4 contains a side-on bound TEMPO– ligand,
which is characterized by a long N–O bond length [1.383(2)
Å]. The contrasting reactivity of Ph2S2 and TEMPO likely relates to their different redox potentials, as
Ph2S2 is a relatively weak oxidant. Finally,
the addition of pyridine-N-oxide to 2 results in the formation of the adduct, [(bipy)Ni(NO)(ONC5H5)][PF6] (5). No evidence of
NO release is observed in this reaction, probably because of the low
one-electron (1e–) reduction potential of pyridine-N-oxide.