Molecular and Electronic Structures of Ruthenium Complexes Containing an ONS-Coordinated Open-Shell π Radical and an Oxidative Aromatic Ring Cleavage Reaction

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 LONS3– is redox-noninnocent and undergoes oxidation to either a closed-shell singlet (CSS), LONS–, or an open-shell π-radical state, LONS•2–, and the reactivities of the [RuII(LONS•2–)] and [RuII(LONS–)] states are different. The reaction of (LONSH2)2 with [Ru­(PPh3)3Cl2] in toluene in the presence of PPh3 affords a ruthenium complex of the type trans-[Ru­(LONS)­(PPh3)2Cl] (1), while the similar reaction with [Ru­(PPh3)3(H)­(CO)­Cl] yields a LONS•2– complex of ruthenium­(II) of the type trans-[RuII(LONS•2–)­(PPh3)2(CO)] (2). 1 is a resonance hybrid of the [RuII(LONS–)­Cl] and [RuIII(LONS•2–)­Cl] states. It is established that 2 incorporating an open-shell π-radical state, [RuII(LONS•2–)­(CO)], reacts with an in situ generated superoxide ion and promotes an oxidative aromatic ring cleavage reaction, yielding a α-N-arylimino-ω-ketocarboxylate (LNS2–) complex of the type [RuII(LNS2–)­(PPh3)­(CO)]2 (4), while 1 having a CSS state, [RuII(LONS–)­Cl], is inert in similar conditions. Notably, 2 does not react with O2 molecule but reacts with KO2 in the presence of excess PPh3, affording 4. The redox reaction of (LONSH2)2 with [Ru­(PPh3)3Cl2] in ethanol in air is different, leading to the oxidation of LONS to a quinone sulfoxide derivative (LONSO0) as in cis-[RuII(LONSO0)­(PPh3)­Cl2] (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 [RuIII(LONS–)­(PPh3)2Cl ↔ RuIV(LONS•2–)­(PPh3)2Cl]+ states, 2– is a LONS3– complex of ruthenium­(II), [RuII(LONS3–)­(PPh3)2(CO)]−, and 2+ is a ruthenium­(II) complex of LONS– of the type [RuII(LONS–)­(PPh3)2(CO)]+, where 35% diradical character of the LONS– ligand was predicted.