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 (LH), which was isolated as a diaryl disulfide form, (LH), with a Ru ion is disclosed. It was established that the trianionic L is redox-noninnocent and undergoes oxidation to either a closed-shell singlet (CSS), L, or an open-shell π-radical state, L, and the reactivities of the [Ru(L)] and [Ru(L)] states are different. The reaction of (LH) with [Ru(PPh)Cl] in toluene in the presence of PPh affords a ruthenium complex of the type trans-[Ru(L)(PPh)Cl] (1), while the similar reaction with [Ru(PPh)(H)(CO)Cl] yields a L complex of ruthenium(II) of the type trans-[Ru(L)(PPh)(CO)] (2). 1 is a resonance hybrid of the [Ru(L)Cl] and [Ru(L)Cl] states. It is established that 2 incorporating an open-shell π-radical state, [Ru(L)(CO)], reacts with an in situ generated superoxide ion and promotes an oxidative aromatic ring cleavage reaction, yielding a α-N-arylimino-ω-ketocarboxylate (L) complex of the type [Ru(L)(PPh)(CO)] (4), while 1 having a CSS state, [Ru(L)Cl], is inert in similar conditions. Notably, 2 does not react with O molecule but reacts with KO in the presence of excess PPh, affording 4. The redox reaction of (LH) with [Ru(PPh)Cl] in ethanol in air is different, leading to the oxidation of L to a quinone sulfoxide derivative (L) as in cis-[Ru(L)(PPh)Cl] (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(L)(PPh)Cl ↔ Ru(L)(PPh)Cl] states, 2 is a L complex of ruthenium(II), [Ru(L)(PPh)(CO)], and 2 is a ruthenium(II) complex of L of the type [Ru(L)(PPh)(CO)], where 35% diradical character of the L ligand was predicted.