The coordination chemistry of 2,4-di-tert-butyl-6-[(2-mercaptophenyl)amino]phenol (LoNsH3), which was isolated as a diaryl disulfide form, (LoNsH2)(2), with a Ru ion is disclosed. It was established that the trianionic L-oNs(3-) is redox-noninnocent and undergoes oxidation to either a closed-shell singlet (CSS), L-oNs(-) or an open-shell pi-radical state, L-oNs(center dot 2-), and the reactivities of the [Ru-II(L-oNs(center dot 2-))] and [Ru-ll(L-oNs(-))] states are different. The reaction of (LoNsH2)(2) with [Ru(PPh3)(3)Cl-2] in toluene in the presence of PPh3 affords a ruthenium complex of the type trans-[Ru(L-oNs)(PPh3)(2)Cl] (1), while the similar reaction with [Ru(PPh3)(3)(H)(CO)Cl] yields a L-oNs(center dot 2-) complex of rutheniurn(II) of the type trans-[Ru-II(L-oNs(.2-))(1)Ph-3)(2)(CO)] (2). 1 is a resonance hybrid of the [Ru-ll(L-oNs)Cl] and [RUIII(L-oNs(.2-))Cl]'' states. It is established that 2, incorporating an open-shell Jr-radical state, [Ru-ll(,L-oNs(.2-))(Cl)], reacts with an in situ generated superoxide ion and promotes an oxidative aromatic ring cleavage reaction, yielding a alpha-N-arylimino-omega-ketocarboxylate (L-Ns(2-)) complex of the type [Ru-II(L-Ns(2-))(PPh3)(CO)](2) (4), while 1 having a CSS state, [Ru-ll(LoNs-)Cl], is inert in similar conditions. Notably, 2 does not react with O-2 molecule but reacts with KO2 in the presence of excess PPh3, affording 4. The redox reaction of (LoNsH2)(2) with [Ru(PPh3)(3)Cl-2] in ethanol in air is different, leading to the oxidation of LONS to a quinone sulfoxide derivative (L-oNs(0)) as in cis-[Ru-II(L-oNs(o))(13Ph(3))Cl-2] (3), via 1 as an intermediate. The molecular and electronic structures of 1-4 were established by single-crystal X-ray crystallography, electron paramagnetic resonance spectroscopy, electrochemical measurements, and density functional theory,calculations. 1(+) is a resonance hybrid of [Ru-III(L-oNs(-))(PPh3)(2)Cl <-> Ru-iv(L-oNs(.2-))(PPh3)(2)Cl] states, 2 is a L(oNs)(3.)complex of ruthenium(II), [Ru-II ( L-oNs(3-))(PPh3)(2)(CO)]-, and 2(+) is a ruthenium(II) complex of LoNs of the "type [Ru-ll(LoNs-PPh3)(2)(CO)], where 35% diradical character of the LoNs ligand was predicted.