A Redox-Active Cascade Precursor: Isolation of a Zwitterionic Triphenylphosphonio–Hydrazyl Radical and an Indazolo–Indazole Derivative

A redox-active [ML] unit (M = Co^II and Mn^II; LH₂ = <i>N</i>′-(1,4-dioxo-1,4-dihydronaphthalen-2-yl)­benzohydrazide) defined as a cascade precursor that undergoes a multicomponent redox reaction comprising of a C–N bond formation, tautomerization, oxidation, C–C coupling, demetalation, and affording 6,14-dibenzoylbenzo­[<i>f</i>]­benzo­[5,6]­indazolo­[3<i>a</i>,3-<i>c</i>]­indazole-5,8,13,16-tetraone (^IndL₂) is reported. Conversion of LH₂ → ^IndL₂ in air is overall a (6H⁺+6e) oxidation reaction, and it opens a route for the syntheses of bioactive diarylindazolo­[3<i>a</i>,3-<i>c</i>]­indazole derivatives. The reaction occurs via a radical coupling reaction, and the radical intermediate was isolated as a triphenylphosphonio adduct. In presence of PPh₃ the [ML] unit promotes a reaction that involves a C–P bond formation, tautomerization, and oxidation to yield a stable zwitterionic triphenylphosphonio-hydrazyl radical (^PPh3L^±•). Conversion of LH₂ → ^PPh3L^±• is a (3H⁺+3e) oxidation reaction. To authenticate the [ML] unit, in addition to the ^IndL₂, a zinc­(II) complex, [(L₃)­Zn^II(H₂O)­Cl]·2MeOH (<b>1</b>·2MeOH), was successfully isolated (L₃H = a pyridazine derivative of 1,4 naphthoquinone) from a reaction of LH₂ with hydrated ZnCl₂. Conversion of 3LH₂ → <b>1</b> is also a multicomponent (6H⁺+6e) oxidation reaction promoted by zinc­(II) ion via a radical intermediate. Facile oxidation of [L^2–] to [L^•–] that was considered as an intermediate of these conversions was confirmed by isolating a 1,4 naphthoquinone-benzhydrazyl radical (LH^•) complex, [(LH^•)­Zn^II(H₂O)­Cl₂] (<b>2H</b>^•). The intermediates of LH₂ → ^IndL₂, LH₂ → ^PPh3L^±•, and 3LH₂ → <b>1</b> conversions were analyzed by electrospray ionization mass spectroscopy. The molecular and electronic structures of ^PPh3L^±•, ^IndL₂, <b>1</b>·2MeOH, and <b>2H</b>^• were confirmed by single-crystal X-ray crystallography, electron paramagnetic resonance spectroscopy, and density functional theory calculations

Ruthenium, Rhodium, Osmium, and Iridium Complexes of Osazones (Osazones = Bis-Arylhydrazones of Glyoxal): Radical versus Nonradical States

Phenyl osazone (L^NHPhH₂), phenyl osazone anion radical (L^NHPhH₂^•–), benzoyl osazone (L^NHCOPhH₂), benzoyl osazone anion radical (L^NHCOPhH₂^•–), benzoyl osazone monoanion (L^NCOPhHMe^–), and anilido osazone (L^NHCONHPhHMe) complexes of ruthenium, osmium, rhodium, and iridium of the types <i>trans</i>-[Os­(L^NHPhH₂)­(PPh₃)₂Br₂] (<b>3</b>), <i>trans</i>-[Ir­(L^NHPhH₂^•–)­(PPh₃)₂Cl₂] (<b>4</b>), <i>trans</i>-[Ru­(L^NHCOPhH₂)­(PPh₃)₂Cl₂] (<b>5</b>), <i>trans</i>-[Os­(L^NHCOPhH₂)­(PPh₃)₂Br₂] (<b>6</b>), <i>trans</i>- [Rh­(L^NHCOPhH₂^•–)­(PPh₃)₂Cl₂] (<b>7</b>), <i>trans</i>-[Rh­(L^NHCOPhHMe^–)­(PPh₃)₂Cl]­PF₆ ([<b>8</b>]­PF₆), and <i>trans</i>-[Ru­(L^NHCONHPhHMe)­(PPh₃)₂Cl]Cl ([<b>9</b>]­Cl) have been isolated and compared (osazones = bis-arylhydrazones of glyoxal). The complexes have been characterized by elemental analyses and IR, mass, and ¹H NMR spectra; in addition, single-crystal X-ray structure determinations of <b>5</b>, <b>6</b>, [<b>8</b>]­PF₆, and [<b>9</b>]Cl have been carried out. EPR spectra of <b>4</b> and <b>7</b> reveal that in the solid state they are osazone anion radical complexes (<b>4</b>, <i>g</i>_av = 1.989; <b>7</b>, 2.028 (Δ<i>g</i> = 0.103)), while in solution the contribution of the M­(II) ions is greater (<b>4</b>, <i>g</i>_av = 2.052 (Δ<i>g</i> = 0.189); <b>7</b>, <i>g</i>_av = 2.102 (Δ<i>g</i> = 0.238)). Mulliken spin densities on L^NHPhH₂ and L^NHCOPhH₂ obtained from unrestricted density functional theory (DFT) calculations on <i>trans</i>-[Ir­(L^NHPhH₂)­(PMe₃)₂Cl₂] (<b>4</b>^Me) and <i>trans</i>-[Rh­(L^NHCOPhH₂)­(PMe₃)₂Cl₂] (<b>7</b>^Me) in the gas phase with doublet spin states authenticated the existence of L^NHPhH₂^•– and L^NHCOPhH₂^•– anion radicals in <b>4</b> and <b>7</b> coordinated to iridium­(III) and rhodium­(III) ions. DFT calculations on <i>trans</i>-[Os­(L^NHPhH₂)­(PMe₃)₂Br₂] (<b>3</b>^Me), <i>trans</i>-[Os­(L^NHCOPhH₂)­(PMe₃)₂Br₂] (<b>6</b>^Me), and <i>trans</i>-[Ru­(L^NHCONHPhHMe^–)­(PMe₃)₂Cl] [<b>9</b>^Me]⁺ with singlet spin states established that the closed-shell singlet state (CSS) solutions of <b>3</b>, <b>5</b>, <b>6</b>, and [<b>9</b>]­Cl are stable. The lower value of M^III/M^II reduction potentials and lower energy absorption bands corroborate the higher extent of mixing of d orbitals with the π* orbital in the case of <b>3</b> and <b>6</b>. Time-dependent (TD) DFT calculations elucidated the MLCT as the origin of the lower energy absorption bands of <b>3</b>, <b>5</b>, and <b>6</b> and π → π* as the origin of transitions in <b>4</b> and <b>7</b>

Ruthenium, Rhodium, Osmium, and Iridium Complexes of Osazones (Osazones = Bis-Arylhydrazones of Glyoxal): Radical versus Nonradical States

Phenyl osazone (L^NHPhH₂), phenyl osazone anion radical (L^NHPhH₂^•–), benzoyl osazone (L^NHCOPhH₂), benzoyl osazone anion radical (L^NHCOPhH₂^•–), benzoyl osazone monoanion (L^NCOPhHMe^–), and anilido osazone (L^NHCONHPhHMe) complexes of ruthenium, osmium, rhodium, and iridium of the types <i>trans</i>-[Os­(L^NHPhH₂)­(PPh₃)₂Br₂] (<b>3</b>), <i>trans</i>-[Ir­(L^NHPhH₂^•–)­(PPh₃)₂Cl₂] (<b>4</b>), <i>trans</i>-[Ru­(L^NHCOPhH₂)­(PPh₃)₂Cl₂] (<b>5</b>), <i>trans</i>-[Os­(L^NHCOPhH₂)­(PPh₃)₂Br₂] (<b>6</b>), <i>trans</i>- [Rh­(L^NHCOPhH₂^•–)­(PPh₃)₂Cl₂] (<b>7</b>), <i>trans</i>-[Rh­(L^NHCOPhHMe^–)­(PPh₃)₂Cl]­PF₆ ([<b>8</b>]­PF₆), and <i>trans</i>-[Ru­(L^NHCONHPhHMe)­(PPh₃)₂Cl]Cl ([<b>9</b>]­Cl) have been isolated and compared (osazones = bis-arylhydrazones of glyoxal). The complexes have been characterized by elemental analyses and IR, mass, and ¹H NMR spectra; in addition, single-crystal X-ray structure determinations of <b>5</b>, <b>6</b>, [<b>8</b>]­PF₆, and [<b>9</b>]Cl have been carried out. EPR spectra of <b>4</b> and <b>7</b> reveal that in the solid state they are osazone anion radical complexes (<b>4</b>, <i>g</i>_av = 1.989; <b>7</b>, 2.028 (Δ<i>g</i> = 0.103)), while in solution the contribution of the M­(II) ions is greater (<b>4</b>, <i>g</i>_av = 2.052 (Δ<i>g</i> = 0.189); <b>7</b>, <i>g</i>_av = 2.102 (Δ<i>g</i> = 0.238)). Mulliken spin densities on L^NHPhH₂ and L^NHCOPhH₂ obtained from unrestricted density functional theory (DFT) calculations on <i>trans</i>-[Ir­(L^NHPhH₂)­(PMe₃)₂Cl₂] (<b>4</b>^Me) and <i>trans</i>-[Rh­(L^NHCOPhH₂)­(PMe₃)₂Cl₂] (<b>7</b>^Me) in the gas phase with doublet spin states authenticated the existence of L^NHPhH₂^•– and L^NHCOPhH₂^•– anion radicals in <b>4</b> and <b>7</b> coordinated to iridium­(III) and rhodium­(III) ions. DFT calculations on <i>trans</i>-[Os­(L^NHPhH₂)­(PMe₃)₂Br₂] (<b>3</b>^Me), <i>trans</i>-[Os­(L^NHCOPhH₂)­(PMe₃)₂Br₂] (<b>6</b>^Me), and <i>trans</i>-[Ru­(L^NHCONHPhHMe^–)­(PMe₃)₂Cl] [<b>9</b>^Me]⁺ with singlet spin states established that the closed-shell singlet state (CSS) solutions of <b>3</b>, <b>5</b>, <b>6</b>, and [<b>9</b>]­Cl are stable. The lower value of M^III/M^II reduction potentials and lower energy absorption bands corroborate the higher extent of mixing of d orbitals with the π* orbital in the case of <b>3</b> and <b>6</b>. Time-dependent (TD) DFT calculations elucidated the MLCT as the origin of the lower energy absorption bands of <b>3</b>, <b>5</b>, and <b>6</b> and π → π* as the origin of transitions in <b>4</b> and <b>7</b>

Tris(2,2′-azobispyridine) Complexes of Copper(II): X‑ray Structures, Reactivities, and the Radical Nonradical Bis(ligand) Analogues

Tris­(abpy) complexes of types <i>mer</i>-[Cu^II(abpy)₃]­[PF₆]₂ (<i>mer</i>-<b>1</b>²⁺[PF₆^–]₂) and ctc-[Cu^II(abpy)₂(bpy)]­[PF₆]₂ (ctc-<b>2</b>²⁺[PF₆^–]₂) were successfully isolated and characterized by spectra and single-crystal X-ray structure determinations (abpy = 2,2′-azobispyridine; bpy = 2,2′-bipyridine). Reactions of <i>mer</i>-<b>1</b>²⁺ and ctc-<b>2</b>²⁺ ions with catechol, <i>o</i>-aminophenol, <i>p-</i>phenylenediamine, and diphenylamine (Ph–NH–Ph) in 2:1 molar ratio afford [Cu^I(abpy)₂]⁺ (<b>3</b>^<b>+</b>) and corresponding quinone derivatives. The similar reactions of [Cu^II(bpy)₃]²⁺ and [Cu^II(phen)₃]²⁺ with these substrates yielding [Cu^I(bpy)₂]⁺ and [Cu^I(phen)₂]⁺ imply that these complexes undergo <i>reduction-induced ligand dissociation</i> reactions (phen = 1,10-phenanthroline). The average −NN– lengths in <i>mer</i>-<b>1</b>²⁺[PF₆^–]₂ and ctc-<b>2</b>²⁺[PF₆^–]₂ are 1.248(4), while that in <b>3</b>⁺[PF₆^–]·2CH₂Cl₂ is relatively longer, 1.275(2) Å, due to d_Cu → π_azo* back bonding. In cyclic voltammetry, <i>mer</i>-<b>1</b>²⁺ exhibits one quasi-reversible wave at −0.42 V due to Cu^II/Cu^I and abpy/abpy^•– couples and two reversible waves at −0.90 and −1.28 V due to abpy/abpy^•– couple, while those of ctc-<b>2</b>²⁺ ion appear at −0.44, −0.86, and −1.10 V versus Fc⁺/Fc couple. The anodic <b>3</b>²⁺/<b>3</b>⁺ and the cathodic <b>3</b>⁺/<b>3</b> redox waves at +0.33 and −0.40 V are reversible. The electron paramagnetic resonance spectra and density functional theory (DFT) calculations authenticated the existence of abpy anion radical (abpy^•–) in <b>3</b>, which is defined as a hybrid state of [Cu^I(abpy^0.5•–)­(abpy^0.5•–)] and [Cu^II(abpy^•–)­(abpy^•–)] states. <b>3</b>²⁺ ion is a neutral abpy complex of copper­(II) of type [Cu^II(abpy)₂]²⁺. <b>3</b> exhibits a near-IR absorption band at 2400–3000 nm because of the intervalence ligand-to-ligand charge transfer, elucidated by time-dependent DFT calculations in CH₂Cl₂

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

Oxidovanadium Catechol Complexes: Radical versus Non-Radical States and Redox Series

A new family of oxidovanadium complexes, [(L₁^R)­(VO)­(L^{R^′})] (R = H, R′ = H, <b>1</b>; R = H, R′ = -CMe₃, <b>2</b>; R = H, R′ = Me, <b>3</b>; R = -CMe₃, R′ = H, <b>4</b> and R = -CMe₃, R′ = -CMe₃, <b>5</b>), incorporating tridentate L₁^RH ligands (L₁^RH = 2,4-di<i>-</i>R-6-{(2-(pyridin-2-yl)­hydrazono)­methyl}­phenol) and substituted catechols (L^{R^′}H₂) was substantiated. The V–O_phenolato (cis to VO), V–O_CAT (cis to VO) and V–O_CAT (trans to VO) lengths span the ranges, 1.894(2)–1.910(2), 1.868(2)–1.887(2), and 2.120(2)–2.180(2) Å. The metrical oxidation states (MOS) of the catechols in <b>1</b>–<b>5</b> are fractional and vary from −1.43 to −1.60. The ⁵¹V isotropic chemical shifts of solids and solutions of <b>1</b>–<b>5</b> are deshielded (⁵¹V CP MAS: −19.8 to +248.6; DMSO-d₆: +173.9 to +414.55 ppm). The closed shell singlet (CSS) solutions of <b>1</b>–<b>5</b> are unstable due to open shell singlet (OSS) perturbations. The ground electronic states of <b>1</b>–<b>5</b> are defined by the resonance contribution of the catecholates (L^{R^′}_CAT^2–) and L^{R^′}_SQ^–• coordinated to the [VO]³⁺ and [VO]²⁺ ions. <b>1</b>–<b>5</b> are reversibly reducible by one electron at −(0.58–0.87) V, referenced vs ferrocenium/ferrocene, to VO²⁺ complexes, [(L₁^R–)­(VO²⁺)­(L^{R^′}_CAT^2–)]⁻ [<b>1</b>–<b>5</b>]⁻. <b>1</b>–<b>5</b> display another quasi-reversible or irreversible reduction wave at −(0.80–1.32) V due to the formation of hydrazone anion radical (L₁^R2–•) complexes, [(L₁^R2–•)­(VO²⁺)­(L^{R^′}_CAT^2–)]^2–, [<b>1</b>–<b>5</b>]^2–, with <i>S</i> = 1 authenticated by the unrestricted density functional theory (DFT) calculations on <b>1</b>^2– and <b>3</b>^2– ions. Frozen glasses electron paramagnetic resonance (EPR) spectra of [<b>1</b>–<b>5</b>]⁻ ions [e.g., for <b>2</b>, <i>g</i>_|| = 1.948, <i>g</i>_⊥ = 1.979, <i>A</i>_|| = 164, <i>A</i>_⊥ = 60] affirmed that [<b>1</b>–<b>5</b>]⁻ ions are the [VO]²⁺ complexes of L^R′_CAT^2–. Spectro-electrochemical measurements and time-dependent DFT (TD DFT) calculations on <b>1</b>, <b>3</b>, <b>1</b>^–, <b>3</b>^–, and <b>1</b>^2– disclosed that the near infrared (NIR) absorption bands of <b>1</b>–<b>5</b> at 800 nm are due to the CSS-OSS metal to ligand charge transfer which are red-shifted in the solid state and disappear in [<b>1</b>–<b>5</b>]⁻ and [<b>1</b>–<b>5</b>]^2– ions

Oxidovanadium Catechol Complexes: Radical versus Non-Radical States and Redox Series

A new family of oxidovanadium complexes, [(L₁^R)­(VO)­(L^{R^′})] (R = H, R′ = H, <b>1</b>; R = H, R′ = -CMe₃, <b>2</b>; R = H, R′ = Me, <b>3</b>; R = -CMe₃, R′ = H, <b>4</b> and R = -CMe₃, R′ = -CMe₃, <b>5</b>), incorporating tridentate L₁^RH ligands (L₁^RH = 2,4-di<i>-</i>R-6-{(2-(pyridin-2-yl)­hydrazono)­methyl}­phenol) and substituted catechols (L^{R^′}H₂) was substantiated. The V–O_phenolato (cis to VO), V–O_CAT (cis to VO) and V–O_CAT (trans to VO) lengths span the ranges, 1.894(2)–1.910(2), 1.868(2)–1.887(2), and 2.120(2)–2.180(2) Å. The metrical oxidation states (MOS) of the catechols in <b>1</b>–<b>5</b> are fractional and vary from −1.43 to −1.60. The ⁵¹V isotropic chemical shifts of solids and solutions of <b>1</b>–<b>5</b> are deshielded (⁵¹V CP MAS: −19.8 to +248.6; DMSO-d₆: +173.9 to +414.55 ppm). The closed shell singlet (CSS) solutions of <b>1</b>–<b>5</b> are unstable due to open shell singlet (OSS) perturbations. The ground electronic states of <b>1</b>–<b>5</b> are defined by the resonance contribution of the catecholates (L^{R^′}_CAT^2–) and L^{R^′}_SQ^–• coordinated to the [VO]³⁺ and [VO]²⁺ ions. <b>1</b>–<b>5</b> are reversibly reducible by one electron at −(0.58–0.87) V, referenced vs ferrocenium/ferrocene, to VO²⁺ complexes, [(L₁^R–)­(VO²⁺)­(L^{R^′}_CAT^2–)]⁻ [<b>1</b>–<b>5</b>]⁻. <b>1</b>–<b>5</b> display another quasi-reversible or irreversible reduction wave at −(0.80–1.32) V due to the formation of hydrazone anion radical (L₁^R2–•) complexes, [(L₁^R2–•)­(VO²⁺)­(L^{R^′}_CAT^2–)]^2–, [<b>1</b>–<b>5</b>]^2–, with <i>S</i> = 1 authenticated by the unrestricted density functional theory (DFT) calculations on <b>1</b>^2– and <b>3</b>^2– ions. Frozen glasses electron paramagnetic resonance (EPR) spectra of [<b>1</b>–<b>5</b>]⁻ ions [e.g., for <b>2</b>, <i>g</i>_|| = 1.948, <i>g</i>_⊥ = 1.979, <i>A</i>_|| = 164, <i>A</i>_⊥ = 60] affirmed that [<b>1</b>–<b>5</b>]⁻ ions are the [VO]²⁺ complexes of L^R′_CAT^2–. Spectro-electrochemical measurements and time-dependent DFT (TD DFT) calculations on <b>1</b>, <b>3</b>, <b>1</b>^–, <b>3</b>^–, and <b>1</b>^2– disclosed that the near infrared (NIR) absorption bands of <b>1</b>–<b>5</b> at 800 nm are due to the CSS-OSS metal to ligand charge transfer which are red-shifted in the solid state and disappear in [<b>1</b>–<b>5</b>]⁻ and [<b>1</b>–<b>5</b>]^2– ions

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

Orthometalation of Dibenzo[1,2]quinoxaline with Ruthenium(II/III), Osmium(II/III/IV), and Rhodium(III) Ions and Orthometalated [RuNO]^6/7 Derivatives

A new family of organometallics of ruthenium­(II/III), osmium­(II/III/IV), and rhodium­(III) ions isolated from C–H activation reactions of dibenzo­[1,2]­quinoxaline (DBQ) using triphenylphosphine, carbonyl, and halides as coligands is reported. The CN–chelate complexes isolated are <i>trans-</i>[Ru^III(DBQ)­(PPh₃)₂Cl₂] (<b>1</b>), <i>trans-</i>[Ru^II(DBQ)­(CO)­(PPh₃)₂Cl] (<b>2</b>), <i>trans-</i>[Os^III(DBQ)­(PPh₃)₂Br₂] (<b>3</b>), <i>trans-</i>[Os^II(DBQ)­(PPh₃)₂(CO)­Br] (<b>4</b>), and <i>trans-</i>[Rh^III(DBQ)­(PPh₃)₂Cl₂] (<b>5</b>). Reaction of <b>1</b> with NO affords <i>trans-</i>[Ru­(DBQ)­(NO)­(PPh₃)₂Cl]Cl (<b>6</b>⁺Cl^–), isoelectronic to <b>2</b>, with a byproduct, [Ru­(NO)­(PPh₃)₂Cl₃] (<b>7</b>). Complexes <b>1</b>–<b>5</b> and <b>6</b>⁺ were characterized by elemental analyses, mass, IR, NMR, and electron paramagnetic resonance (EPR) spectra including the single-crystal X-ray structure determinations of <b>1</b>–<b>3</b> and <b>5</b>. The Ru^III–C, Ru^II–C, Os^III–C, and Rh^III–C lengths are 2.049(2), 2.074(3), 2.105(16), and 2.012(3) Å in <b>1</b>, <b>2</b>, <b>3</b>, and <b>5</b>. In cyclic voltammetry, <b>2</b>, <b>3</b>, and <b>4</b> undergo oxidation at 0.59, 0.39, and 0.46 V, versus Fc⁺/Fc couple, to <i>trans-</i>[Ru^III(DBQ)­(CO)­(PPh₃)₂Cl]⁺ (<b>2</b>⁺), <i>trans-</i>[Os^IV(DBQ)­(PPh₃)₂Br₂]⁺ (<b>3</b>⁺), and <i>trans-</i>[Os^III(DBQ)­(CO)­(PPh₃)₂Br]⁺ (<b>4</b>⁺) ions. Complex <b>3</b>⁺ incorporates an Os^IV(d⁴ ion)–C bond. The <b>6</b>⁺/<i>trans-</i>[Ru­(DBQ)­(NO)­(PPh₃)₂Cl] (<b>6</b>) reduction couple at −0.65 V is reversible. <b>2</b>⁺, <b>3</b>⁺, <b>4</b>⁺ and <b>6</b> were substantiated by spectroelectrochemical measurements, EPR spectra, and density functional theory (DFT) and time-dependent (TD) DFT calculations. The frozen-glass EPR spectrum of the electrogenerated <b>6</b> exhibits hyperfine couplings due to ^99,101Ru and ¹⁴N nuclei. DFT calculations on <i>trans-</i>[Os^III(DBQ)­(PMe₃)₂Br₂] (<b>3</b>^Me), S_t = 1/2 and <i>trans-</i>[Os^IV(DBQ)­(PMe₃)₂Br₂]⁺ (<b>3</b>^Me+), S_t = 0, <i>trans-</i>[Ru­(DBQ)­(NO)­(PMe₃)₂Cl]⁺ (<b>6</b>^Me+), S_t = 0 and <i>trans-</i>[Ru­(DBQ)­(NO)­(PMe₃)₂Cl] (<b>6</b>^Me), S_t = 1/2, authenticated a significant mixing between d_Os and π_aromatic* orbitals, which stabilizes M^II/III/IV–C bonds and the [RuNO]⁶ and [RuNO]⁷ states, respectively, in <b>6</b>⁺ and <b>6</b>, which is defined as a hybrid state of <i>trans-</i>[Ru^II(DBQ)­(NO^•)­(PPh₃)₂Cl] and <i>trans-</i>[Ru^I(DBQ)­(NO⁺)­(PPh₃)₂Cl] states