Cobalt Ion Promoted Redox Cascade: A Route to Spiro Oxazine-Oxazepine Derivatives and a Dinuclear Cobalt(III) Complex of an <i>N</i>‑(1,4-Naphthoquinone)‑<i>o</i>‑aminophenol Derivative

The study discloses that the redox activity of <i>N</i>-(1,4-naphthoquinone)-<i>o</i>-aminophenol derivatives (L^RH₂) containing a (phenol)-NH-(1,4-naphthoquinone) fragment is notably different from that of a (phenol)-NH-(phenol) precursor. The former is a platform for a redox cascade. L^RH₂ is redox noninnocent and exists in Cat-N-(1,4-naphthoquinone)(2−) (L^R 2–) and SQ-N-(1,4-naphthoquinone) (L^R •–) states in the complexes. Reactions of L^RH₂ with cobalt­(II) salts in MeOH in air promote a cascade affording spiro oxazine-oxazepine derivatives (^OXL^R) in good yields, when R = H, Me, ^tBu. Spiro oxazine-oxazepine derivatives are bioactive, and such a molecule has so far not been isolated by a schematic route. In this context this cascade is significant. Dimerization of L^RH₂ → ^OXL^R in MeOH is a (6H⁺ + 6e) oxidation reaction and is composed of formations of four covalent bonds and 6-exo-trig and 7-endo-trig cyclization based on C–O coupling reactions, where MeOH is the source of a proton and the ester function. It was established that the active cascade precursor is [(L^Me •–)­Co^IIICl₂] (<b>A</b>). Notably, formation of a spiro derivative was not detected in CH₃CN and the reaction ends up furnishing <b>A</b>. The route of the reaction is tunable by R, when R = NO₂, it is a (2e + 4H⁺) oxidation reaction affording a dinuclear L^R 2– complex of cobalt­(III) of the type [(L^NO2 2–)₂Co^III₂(OMe)₂(H₂O)₂] (<b>1</b>) in good yields. No cascade occurs with zinc­(II) ion even in MeOH and produces a L^Me •– complex of type [(L^Me •–)­Zn^IICl₂] (<b>2</b>). The intermediate <b>A</b> and <b>2</b> exhibit strong EPR signals at <i>g</i> = 2.008 and 1.999, confrming the existence of L^Me •– coordinated to low-spin cobalt­(III) and zinc­(II) ions. The intermediates of L^RH₂ → ^OXL^R conversion were analyzed by ESI mass spectrometry. The molecular geometries of ^OXL^R and <b>1</b> were confirmed by X-ray crystallography, and the spectral features were elucidated by TD DFT calculations

Radical and Non-Radical States of the [Os(PIQ)] Core (PIQ = 9,10-Phenanthreneiminoquinone): Iminosemiquinone to Iminoquinone Conversion Promoted <i>o</i>‑Metalation Reaction

The coordination and redox chemistry of 9,10-phenanthreneiminoquinone (PIQ) with osmium ion authenticating the [Os^II(PIQ^•–)], [Os^III(PIQ^•–)], [Os^III(C,N-PIQ)], [Os^III(PIQ)], and [Os^III(PIQ^2–) ] states of the [Os­(PIQ)] core in the complexes of types <i>trans-</i>[Os^II(PIQ^•–)­(PPh₃)₂(CO)­Br] (<b>1</b>), <i>trans-</i>[Os^III(PIQ^•–)­(PPh₃)₂Br₂] (<b>2</b>), <i>trans-</i>[Os^III(C,N-PIQ)­(PPh₃)₂Br₂]·2CH₂Cl₂ (<b>3</b>·2CH₂Cl₂), <i>trans-</i>[Os^III(C,N-PIQ^Br)­(PPh₃)₂Br₂]·2CH₂Cl₂ (<b>4</b>·2CH₂Cl₂), <i>trans-</i>[Os^III(C,N-PIQ^Cl2)­(PPh₃)₂Br₂] (<b>6</b>), <i>trans-</i>[Os^III(PIQ^•–)­(PPh₃)₂Br₂]⁺1/2I₃^–1/2Br^– (<b>1</b>⁺1/2I₃^–1/2Br^–), [Os^III(PIQ)­(PPh₃)₂Br₂]⁺ (<b>2</b>⁺), and [Os^III(PIQ^2–)­(PPh₃)₂Br₂]⁻ (<b>2</b>^–) are reported (PIQ^•– = 9,10-phenanthreneiminosemiquinonate anion radical; C,N-PIQ = ortho-metalated PIQ, C,N-PIQ^Br = ortho-metalated 4-bromo PIQ, and C,N-PIQ^Cl2 = ortho-metalated 3,4-dichloro PIQ). Reduction of PIQ by [Os^II(PPh₃)₃(H)­(CO)­Br] affords <b>1</b>, while the reaction of PIQ with [Os^II(PPh₃)₃Br₂] furnishes <b>2</b>. Oxidation of <b>1</b> with I₂ affords <b>1</b>⁺1/2I₃^–1/2Br^–, while the similar reactions of <b>2</b> with X₂ (X = I, Br, Cl) produce the ortho-metalated derivatives <b>3</b>·2CH₂Cl₂, <b>4</b>·2CH₂Cl₂, and <b>6</b>. PIQ and PIQ^2– complexes of osmium­(III), <b>2</b>^<b>+</b> and <b>2</b>^<b>‑</b>, are generated by constant-potential electrolysis. However, <b>2</b>⁺ ion is unstable in solution and slowly converts to <b>3</b> and partially hydrolyzes to <i>trans-</i>[Os^III(PQ^•–)­(PPh₃)₂Br₂] (<b>2</b>_<b>PQ</b>), a PQ^•– analogue of <b>2</b>. Conversion of <b>2</b>⁺ → <b>3</b> in solution excludes the formation of aryl halide as an intermediate for this unique ortho-metalation reaction at 295 K, where PIQ acts as a redox-noninnocent ambidentate ligand. In the complexes, the PIQ^•– state where the atomic spin is more localized on the nitrogen atom is stable and is more abundant. The reaction of <b>2</b>_<b>PQ</b>, with I₂ does not promote any ortho-metalation reaction and yields a PQ complex of type <i>trans-</i>[Os^III(PQ)­(PPh₃)₂Br₂]⁺I₅^–·2CH₂Cl₂ (<b>5</b>⁺I₅^–·2CH₂Cl₂). The molecular and electronic structures of <b>1</b>–<b>4</b>, <b>6</b>, <b>1</b>⁺, and <b>5</b>⁺ were established by different spectra, single-crystal X-ray bond parameters, cyclic voltammetry, and DFT calculations

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-<i>tert</i>-butyl-6-[(2-mercaptophenyl)­amino]­phenol (L_ONSH₃), which was isolated as a diaryl disulfide form, (L_ONSH₂)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 π-radical state, L_ONS^•2–, and the reactivities of the [Ru^II(L_ONS^•2–)] and [Ru^II(L_ONS^–)] states are different. The reaction of (L_ONSH₂)₂ with [Ru­(PPh₃)₃Cl₂] in toluene in the presence of PPh₃ affords a ruthenium complex of the type <i>trans</i>-[Ru­(L_ONS)­(PPh₃)₂Cl] (<b>1</b>), while the similar reaction with [Ru­(PPh₃)₃(H)­(CO)­Cl] yields a L_ONS^•2– complex of ruthenium­(II) of the type <i>trans</i>-[Ru^II(L_ONS^•2–)­(PPh₃)₂(CO)] (<b>2</b>). <b>1</b> is a resonance hybrid of the [Ru^II(L_ONS^–)­Cl] and [Ru^III(L_ONS^•2–)­Cl] states. It is established that <b>2</b> incorporating an open-shell π-radical state, [Ru^II(L_ONS^•2–)­(CO)], reacts with an in situ generated superoxide ion and promotes an oxidative aromatic ring cleavage reaction, yielding a α-<i>N</i>-arylimino-ω-ketocarboxylate (L_NS^2–) complex of the type [Ru^II(L_NS^2–)­(PPh₃)­(CO)]₂ (<b>4</b>), while <b>1</b> having a CSS state, [Ru^II(L_ONS^–)­Cl], is inert in similar conditions. Notably, <b>2</b> does not react with O₂ molecule but reacts with KO₂ in the presence of excess PPh₃, affording <b>4</b>. The redox reaction of (L_ONSH₂)₂ with [Ru­(PPh₃)₃Cl₂] in ethanol in air is different, leading to the oxidation of L_ONS to a quinone sulfoxide derivative (L_ONSO⁰) as in <i>cis</i>-[Ru^II(L_ONSO⁰)­(PPh₃)­Cl₂] (<b>3</b>), via <b>1</b> as an intermediate. The molecular and electronic structures of <b>1</b>–<b>4</b> were established by single-crystal X-ray crystallography, electron paramagnetic resonance spectroscopy, electrochemical measurements, and density functional theory calculations. <b>1</b>⁺ is a resonance hybrid of [Ru^III(L_ONS^–)­(PPh₃)₂Cl ↔ Ru^IV(L_ONS^•2–)­(PPh₃)₂Cl]⁺ states, <b>2</b>^– is a L_ONS^3– complex of ruthenium­(II), [Ru^II(L_ONS^3–)­(PPh₃)₂(CO)]⁻, and <b>2</b>⁺ is a ruthenium­(II) complex of L_ONS^– of the type [Ru^II(L_ONS^–)­(PPh₃)₂(CO)]⁺, where 35% diradical character of the L_ONS^– ligand was predicted

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-<i>tert</i>-butyl-6-[(2-mercaptophenyl)­amino]­phenol (L_ONSH₃), which was isolated as a diaryl disulfide form, (L_ONSH₂)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 π-radical state, L_ONS^•2–, and the reactivities of the [Ru^II(L_ONS^•2–)] and [Ru^II(L_ONS^–)] states are different. The reaction of (L_ONSH₂)₂ with [Ru­(PPh₃)₃Cl₂] in toluene in the presence of PPh₃ affords a ruthenium complex of the type <i>trans</i>-[Ru­(L_ONS)­(PPh₃)₂Cl] (<b>1</b>), while the similar reaction with [Ru­(PPh₃)₃(H)­(CO)­Cl] yields a L_ONS^•2– complex of ruthenium­(II) of the type <i>trans</i>-[Ru^II(L_ONS^•2–)­(PPh₃)₂(CO)] (<b>2</b>). <b>1</b> is a resonance hybrid of the [Ru^II(L_ONS^–)­Cl] and [Ru^III(L_ONS^•2–)­Cl] states. It is established that <b>2</b> incorporating an open-shell π-radical state, [Ru^II(L_ONS^•2–)­(CO)], reacts with an in situ generated superoxide ion and promotes an oxidative aromatic ring cleavage reaction, yielding a α-<i>N</i>-arylimino-ω-ketocarboxylate (L_NS^2–) complex of the type [Ru^II(L_NS^2–)­(PPh₃)­(CO)]₂ (<b>4</b>), while <b>1</b> having a CSS state, [Ru^II(L_ONS^–)­Cl], is inert in similar conditions. Notably, <b>2</b> does not react with O₂ molecule but reacts with KO₂ in the presence of excess PPh₃, affording <b>4</b>. The redox reaction of (L_ONSH₂)₂ with [Ru­(PPh₃)₃Cl₂] in ethanol in air is different, leading to the oxidation of L_ONS to a quinone sulfoxide derivative (L_ONSO⁰) as in <i>cis</i>-[Ru^II(L_ONSO⁰)­(PPh₃)­Cl₂] (<b>3</b>), via <b>1</b> as an intermediate. The molecular and electronic structures of <b>1</b>–<b>4</b> were established by single-crystal X-ray crystallography, electron paramagnetic resonance spectroscopy, electrochemical measurements, and density functional theory calculations. <b>1</b>⁺ is a resonance hybrid of [Ru^III(L_ONS^–)­(PPh₃)₂Cl ↔ Ru^IV(L_ONS^•2–)­(PPh₃)₂Cl]⁺ states, <b>2</b>^– is a L_ONS^3– complex of ruthenium­(II), [Ru^II(L_ONS^3–)­(PPh₃)₂(CO)]⁻, and <b>2</b>⁺ is a ruthenium­(II) complex of L_ONS^– of the type [Ru^II(L_ONS^–)­(PPh₃)₂(CO)]⁺, where 35% diradical character of the L_ONS^– ligand was predicted