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 (LONS H3 ), which was isolated as a diaryl disulfide form, (LONS H2 )2 , with a Ru ion is disclosed. It was established that the trianionic LONS 3- 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 (LONS H2 )2 with [Ru(PPh3 )3 Cl2 ] in toluene in the presence of PPh3 affords a ruthenium complex of the type trans-[Ru(LONS )(PPh3 )2 Cl] (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 (LNS 2- ) complex of the type [RuII (LNS 2- )(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 (LONS H2 )2 with [Ru(PPh3 )3 Cl2 ] in ethanol in air is different, leading to the oxidation of LONS to a quinone sulfoxide derivative (LONSO 0 ) as in cis-[RuII (LONSO 0 )(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 )2 Cl ↔ RuIV (LONS •2- )(PPh3 )2 Cl]+ states, 2- is a LONS 3- complex of ruthenium(II), [RuII (LONS 3- )(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.