The Electron-Rich {Ru(acac)₂} Directed Varying Configuration of the Deprotonated Indigo and Evidence for Its Bidirectional Noninnocence

This article highlights the hitherto unexplored varying binding modes of the deprotonated natural dye indigo (H₂L) and its bidirectional noninnocent potential. The reaction of H₂L with the selective metal precursor Ru^II(acac)₂(CH₃CN)₂ (acac^– = acetylacetonate) leads to the simultaneous formation of paramagnetic Ru^III(acac)₂(HL^–) (<b>1</b>; blue solid) and diamagnetic Ru^II(acac)₂(L) (<b>2</b>; red solid), which have been characterized by standard analytical, spectroscopic, and structural analysis. Crystal structures establish that the usual <i>trans</i> configurated and twisted monodeprotonated HL^– and unprecedented <i>cis</i> configurated nearly planar dehydroindigo (L) bind to the {Ru­(acac)₂} metal fragment via the N^–,O and N,N donors, forming six- and five-membered chelates, respectively. It also reveals the existence of intramolecular N–H···O hydrogen-bonding interaction between the NH proton and CO group at the back face of the coordinated HL^–, in addition to an intermolecular N–H···O hydrogen bonding between the NH proton of HL^– of Molecule B and oxygen atom of the nearby acac of the second molecule (Molecule A) in the asymmetric unit of <b>1</b>. The specific role of the electron-rich {Ru­(acac)₂} metal fragment in stabilizing the <i>cis</i>-configuration of the electron-deficient L in <b>2</b> has been pointed out. Both <b>1</b> and <b>2</b> exhibit reversible one-electron oxidation and successive three reductions with varying <i>K</i>_c (comproportionation constant) values in the range of 10¹⁸–10⁶. The potentials for the redox processes of <b>2</b> are positively shifted with respect to those of <b>1</b>. The involvement of the metal or HL^–/L or mixed metal-HL^–/L-based orbitals in the accessible redox processes of <b>1</b>^<i>n</i> and <b>2</b>^<i>n</i> has been analyzed by spectroelectrochemistry, EPR at the paramagnetic states, and DFT calculated MO compositions/spin density distributions. The collective consideration of the experimental results and DFT/TD-DFT data has ascertained the participation of both the metal fragment {Ru­(acac)₂} and the HL^–/L in the redox processes, which in effect result in mixed electronic structural forms of <b>1</b>^<i>n</i> and <b>2</b>^<i>n</i> (<i>n</i> = +1, 0, −1, −2, −3)

Ruthenium Derivatives of in Situ Generated Redox-Active 1,2-Dinitrosobenzene and 2‑Nitrosoanilido. Diverse Structural and Electronic Forms

The article describes one-pot synthesis and structural elucidation of <i>tc</i>-[Ru^II(pap)₂(L^•–)]­ClO₄ [<b>1</b>]­ClO₄ and <i>tc</i>-[Ru^II(pap)₂(L′^–)]­ClO₄ [<b>2</b>]­ClO₄, which were obtained from <i>tc</i>-[Ru^II(pap)₂(EtOH)₂]­(ClO₄)₂ and benzofuroxan (L = 1,2-dinitrosobenzene, an intermediate tautomeric form of the biologically active benzofuroxan, L′^– = 2-nitrosoanilido, pap = 2-phenylazopyridine, <i>tc</i> = <i>trans</i> and <i>cis</i> corresponding to pyridine and azo nitrogen donors of pap, respectively). The same reaction with the newly synthesized and structurally characterized metal precursor <i>cc</i>-Ru^II(2,6-dichloropap)₂Cl₂, however, affords isomeric <i>ct</i>-[Ru^II(2,6-dichloropap)₂(L^•–)]⁺ (<b>3a</b>⁺) and <i>tc</i>-[Ru^II(2,6-dichloropap)₂(L^•–)]^<b>+</b> (<b>3b</b>⁺) (<i>cc</i>, <i>ct</i>, and <i>tc</i> with respect to pyridine and azo nitrogens of 2,6-dichloropap) with the structural authentication of elusive <i>ct</i>-isomeric form of {Ru­(pap)₂} family. The impact of <i>trans</i> or <i>cis</i> orientation of the nitroso group of L/L′ with respect to the NN (azo) function of pap in the complexes was reflected in the relative lengthening or shortening of the latter distance, respectively. The redox-sensitive bond parameters of <b>1</b>⁺ and <b>3</b>⁺ reveal the intermediate radical form of L^•–, while <b>2</b>⁺ involves in situ generated L′^–. The multiple redox processes of the complexes in CH₃CN are analyzed via experimental and density functional theory (DFT) and time-dependent DFT calculations. One-electron oxidation of the electron paramagnetic resonance-active radical species (<b>1</b>⁺ and <b>3</b>⁺) leads to [Ru^II(pap)₂(L)]²⁺ involving fully oxidized L⁰ in <b>1</b>²⁺ and <b>3</b>²⁺; the same in <b>2</b>⁺ results in a radical species [Ru^II(pap)₂(L′^•)]²⁺ (<b>2</b>²⁺). Successive reductions in each case are either associated with pap or L/L′^–-based orbitals, revealing a competitive scenario relating to their π-accepting features. The isolated or electrochemically generated radical species either by oxidation or reduction exhibits near-IR transitions in each case, attributing diverse electronic structures of the complexes in accessible redox states

The Electron-Rich {Ru(acac)₂} Directed Varying Configuration of the Deprotonated Indigo and Evidence for Its Bidirectional Noninnocence

This article highlights the hitherto unexplored varying binding modes of the deprotonated natural dye indigo (H₂L) and its bidirectional noninnocent potential. The reaction of H₂L with the selective metal precursor Ru^II(acac)₂(CH₃CN)₂ (acac^– = acetylacetonate) leads to the simultaneous formation of paramagnetic Ru^III(acac)₂(HL^–) (<b>1</b>; blue solid) and diamagnetic Ru^II(acac)₂(L) (<b>2</b>; red solid), which have been characterized by standard analytical, spectroscopic, and structural analysis. Crystal structures establish that the usual <i>trans</i> configurated and twisted monodeprotonated HL^– and unprecedented <i>cis</i> configurated nearly planar dehydroindigo (L) bind to the {Ru­(acac)₂} metal fragment via the N^–,O and N,N donors, forming six- and five-membered chelates, respectively. It also reveals the existence of intramolecular N–H···O hydrogen-bonding interaction between the NH proton and CO group at the back face of the coordinated HL^–, in addition to an intermolecular N–H···O hydrogen bonding between the NH proton of HL^– of Molecule B and oxygen atom of the nearby acac of the second molecule (Molecule A) in the asymmetric unit of <b>1</b>. The specific role of the electron-rich {Ru­(acac)₂} metal fragment in stabilizing the <i>cis</i>-configuration of the electron-deficient L in <b>2</b> has been pointed out. Both <b>1</b> and <b>2</b> exhibit reversible one-electron oxidation and successive three reductions with varying <i>K</i>_c (comproportionation constant) values in the range of 10¹⁸–10⁶. The potentials for the redox processes of <b>2</b> are positively shifted with respect to those of <b>1</b>. The involvement of the metal or HL^–/L or mixed metal-HL^–/L-based orbitals in the accessible redox processes of <b>1</b>^<i>n</i> and <b>2</b>^<i>n</i> has been analyzed by spectroelectrochemistry, EPR at the paramagnetic states, and DFT calculated MO compositions/spin density distributions. The collective consideration of the experimental results and DFT/TD-DFT data has ascertained the participation of both the metal fragment {Ru­(acac)₂} and the HL^–/L in the redox processes, which in effect result in mixed electronic structural forms of <b>1</b>^<i>n</i> and <b>2</b>^<i>n</i> (<i>n</i> = +1, 0, −1, −2, −3)

Indazole-Derived Mono-/Diruthenium and Heterotrinuclear Complexes: Switchable Binding Mode, Electronic Form, and Anion Sensing Events

The article deals with the newer classes of mononuclear: [(acac)2RuIII(H-Iz)(Iz–)] 1, [(acac)2RuIII(H-Iz)2]ClO4 [1]ClO4/[1′]ClO4, and [(bpy)2RuII(H-Iz)(Iz–)]ClO4 [2]ClO4, mixed-valent unsymmetric dinuclear: [(acac)2RuIII(μ-Iz–)2RuII(bpy)2]ClO4 [3]ClO4, and heterotrinuclear: [(acac)2RuIII(μ-Iz–)2MII(μ-Iz–)2RuIII(acac)2] (M = Co:4a, Ni:4b, Cu:4c, and Zn:4d) complexes (H-Iz = indazole, Iz– = indazolate, acac = acetylacetonate, and bpy = 2,2′-bipyridine). Structural characterization of all the aforestated complexes established their molecular identities including varying binding modes (Na and Nb donors and 1H-indazole versus 2H-indazole) of the heterocyclic H-Iz/Iz– in the complexes. Unlike [1′]ClO4 containing two NH protons at the backface of H-Iz units, the corresponding [1]ClO4 was found to be unstable due to the deprotonation of its positively charged quaternary nitrogen center, and this resulted in the eventual formation of the parent complex 1. A combination of experimental and density functional theory calculations indicated the redox noninnocent feature of Iz– in the complexes along the redox chain. The absence of intervalence charge transfer transition in the near-infrared region of the (Iz–)2-bridged unsymmetric mixed-valent RuIIIRuII state in [3]ClO4 suggested negligible intramolecular electronic coupling corresponding to a class I setup (Robin and Day classification). Heterotrinuclear complexes (4a–4d) exhibited varying spin configurations due to spin–spin interactions between the terminal Ru(III) ions and the central M(II) ion. Though both [3]ClO4 and 4a–4d displayed ligand (Iz–/Iz•)-based oxidation, reductions were preferentially taken place at the bpy and metal (RuIII/RuII) centers, respectively. Unlike 1 or [2]ClO4 containing one free NH proton at the backface of H-Iz, [1′]ClO4 with two H-Iz units could selectively and effectively recognize F–, OAc–, and CN– among the tested anions: F–, OAc–, CN–, Cl–, Br–, I–, SCN–, HSO4–, and Η2PΟ4– in CH3CN via intermolecular NH···anion hydrogen bonding interaction. The difference in the sensing feature between [1′]ClO4 and 1/[2]ClO4 could be rationalized by their pKa values of 8.4 and 11.3/10.8, respectively

Ruthenium-Hydride Mediated Unsymmetrical Cleavage of Benzofuroxan to 2‑Nitroanilido with Varying Coordination Mode

The reaction of R-benzofuroxan (R = H, Me, Cl) with the metal precursor [Ru­(Cl)­(H)­(CO)­(PPh₃)₃] (<b>A</b>) or [Ru­(Cl)­(H)­(CH₃CN)­(CO)­(PPh₃)₂] (<b>B</b>) in CH₃CN at 298 K resulted in the intermediate complex [Ru­(Cl)­(L¹)­(CH₃CN)­(CO)­(PPh₃)₂] (L¹ = monodentate 2-nitroanilido) (<b>1</b>, pink), which however underwent slow transformation to the final product [Ru­(Cl)­(L²)­(CO)­(PPh₃)₂] (L² = bidentate 2-nitroanilido) (<b>2</b>, green). On the contrary, the same reaction in refluxing CH₃CN directly yielded <b>2</b> without any tractable intermediate <b>1</b>. Structural characterization of the intermediates <b>1a</b>–<b>1c</b> and the corresponding final products <b>2a</b>–<b>2c</b> (R = H, Me, Cl) authenticated their identities, revealing ruthenium-hydride mediated unsymmetrical cleavage of benzofuroxan to hydrogen bonded monodentate 2-nitroanilido (L¹) in the former and bidentate 2-nitroanilido (L²) in the latter. The spectrophotometric monitoring of the transformations of <b>B</b> → <b>1</b> as well as <b>1</b> → <b>2</b> with time and temperature established the first order rate process with associatively activated pathway for both cases. Both <b>1</b> and <b>2</b> exhibited one reversible oxidation and an irreversible reduction within ±1.5 V versus saturated calomel reference electrode in CH₃CN with slight variation in potential based on substituents in the benzofuroxan framework (R = H, Me, Cl). Spectroscopic (electron paramagnetic resonance and UV–vis) and density functional theory calculations collectively suggested varying contribution of metal based orbitals along with the ligand in the singly occupied molecular orbital of <b>1</b>⁺ or <b>2</b>⁺, ascertaining the noninnocent potential of the in situ generated (L¹) or (L²)

Revelation of Varying Bonding Motif of Alloxazine, a Flavin Analogue, in Selected Ruthenium(II/III) Frameworks

The reaction of alloxazine (L) and Ru^II(acac)₂(CH₃CN)₂ (acac^– = acetylacetonate) in refluxing methanol leads to the simultaneous formation of Ru^II(acac)₂(L) (<b>1</b> = bluish-green) and Ru^III(acac)₂(L^–) (<b>2</b> = red) encompassing a usual neutral α-iminoketo chelating form of L and an unprecedented monodeprotonated α-iminoenolato chelating form of L^–, respectively. The crystal structure of <b>2</b> establishes that N5,O4^– donors of L^– result in a nearly planar five-membered chelate with the {Ru^III(acac)₂⁺} metal fragment. The packing diagram of <b>2</b> further reveals its hydrogen-bonded dimeric form as well as π–π interactions between the nearly planar tricyclic rings of coordinated alloxazine ligands in nearby molecules. The paramagnetic <b>2</b> and one-electron-oxidized <b>1</b>⁺ display ruthenium­(III)-based anisotropic axial EPR in CH₃CN at 77 K with ⟨<i>g</i>⟩/Δ<i>g</i> of 2.136/0.488 and 2.084/0.364, respectively (⟨<i>g</i>⟩ = {1/3­(<i>g</i>₁² + <i>g</i>₂² + <i>g</i>₃²)}^1/2 and Δ<i>g</i> = <i>g</i>₁ – <i>g</i>₃). The multiple electron-transfer processes of <b>1</b> and <b>2</b> in CH₃CN have been analyzed by DFT-calculated MO compositions and Mulliken spin density distributions at the paramagnetic states, which suggest successive two-electron uptake by the π-system of the heterocyclic ring of L (L → L^•– → L^2–) or L^– (L^– → L^•2– → L^3–) besides metal-based (Ru^II/Ru^III) redox process. The origin of the ligand as well as mixed metal–ligand-based multiple electronic transitions of <b>1</b>^<i>n</i> (<i>n</i> = +1, 0, −1, −2) and <b>2</b>^<i>n</i> (<i>n</i> = 0, −1, −2) in the UV and visible regions, respectively, has been assessed by TD-DFT calculations in each redox state. The p<i>K</i>_a values of <b>1</b> and <b>2</b> incorporating two and one NH protons of 6.5 (N3H, p<i>K</i>_a1)/8.16 (N1H, p<i>K</i>_a2) and 8.43 (N1H, p<i>K</i>_a1), respectively, are estimated by monitoring their spectral changes as a function of pH in CH₃CN–H₂O (1:1). <b>1</b> and <b>2</b> in CH₃CN also participate in proton-driven internal reorganizations involving the coordinated alloxazine moiety, i.e., transformation of an α-iminoketo chelating form to an α-iminoenolato chelating form and the reverse process without any electron-transfer step: Ru^II(acac)₂(L) (<b>1</b>) → Ru^II(acac)₂(L^–) (<b>2</b>^–) and Ru^III(acac)₂(L^–) (<b>2</b>) → Ru^III(acac)₂(L) (<b>1</b>⁺)

Ru-Complex Framework toward Aerobic Oxidative Transformations of β‑Diketiminate and α‑Ketodiimine

The impact of the {Ru­(acac)₂} (acac^– = acetylacetonate) framework on the transformations of C–H and C–H/C–C bonds of coordinated β-diketiminate and ketodiimine scaffolds, respectively, has been addressed. It includes the following transformations involving {Ru­(acac)₂} coordinated β-diketiminate in <b>1</b> and ketodiimine in <b>2</b> with the simultaneous change in metal oxidation state: (i) insertion of oxygen into the C­(sp²)–H bond of β-diketiminate in <b>1</b>, leading to the metalated ketodiimine in <b>2</b> and (ii) Bronsted acid (CH₃COOH) assisted cleavage of unstrained C­(sp²)–C­(sp²)/CN bonds of chelated ketodiimine (<b>2</b>) with the concomitant formation of intramolecular C–N bond in <b>3</b>, as well as insertion of oxygen into the C­(sp³)–H bond of <b>2</b> to yield −CHO function in <b>4</b> (−CH₃ → −CHO). The aforesaid transformation processes have been authenticated via structural elucidation of representative complexes and spectroscopic and electrochemical investigations

Revelation of Varying Bonding Motif of Alloxazine, a Flavin Analogue, in Selected Ruthenium(II/III) Frameworks

The reaction of alloxazine (L) and Ru^II(acac)₂(CH₃CN)₂ (acac^– = acetylacetonate) in refluxing methanol leads to the simultaneous formation of Ru^II(acac)₂(L) (<b>1</b> = bluish-green) and Ru^III(acac)₂(L^–) (<b>2</b> = red) encompassing a usual neutral α-iminoketo chelating form of L and an unprecedented monodeprotonated α-iminoenolato chelating form of L^–, respectively. The crystal structure of <b>2</b> establishes that N5,O4^– donors of L^– result in a nearly planar five-membered chelate with the {Ru^III(acac)₂⁺} metal fragment. The packing diagram of <b>2</b> further reveals its hydrogen-bonded dimeric form as well as π–π interactions between the nearly planar tricyclic rings of coordinated alloxazine ligands in nearby molecules. The paramagnetic <b>2</b> and one-electron-oxidized <b>1</b>⁺ display ruthenium­(III)-based anisotropic axial EPR in CH₃CN at 77 K with ⟨<i>g</i>⟩/Δ<i>g</i> of 2.136/0.488 and 2.084/0.364, respectively (⟨<i>g</i>⟩ = {1/3­(<i>g</i>₁² + <i>g</i>₂² + <i>g</i>₃²)}^1/2 and Δ<i>g</i> = <i>g</i>₁ – <i>g</i>₃). The multiple electron-transfer processes of <b>1</b> and <b>2</b> in CH₃CN have been analyzed by DFT-calculated MO compositions and Mulliken spin density distributions at the paramagnetic states, which suggest successive two-electron uptake by the π-system of the heterocyclic ring of L (L → L^•– → L^2–) or L^– (L^– → L^•2– → L^3–) besides metal-based (Ru^II/Ru^III) redox process. The origin of the ligand as well as mixed metal–ligand-based multiple electronic transitions of <b>1</b>^<i>n</i> (<i>n</i> = +1, 0, −1, −2) and <b>2</b>^<i>n</i> (<i>n</i> = 0, −1, −2) in the UV and visible regions, respectively, has been assessed by TD-DFT calculations in each redox state. The p<i>K</i>_a values of <b>1</b> and <b>2</b> incorporating two and one NH protons of 6.5 (N3H, p<i>K</i>_a1)/8.16 (N1H, p<i>K</i>_a2) and 8.43 (N1H, p<i>K</i>_a1), respectively, are estimated by monitoring their spectral changes as a function of pH in CH₃CN–H₂O (1:1). <b>1</b> and <b>2</b> in CH₃CN also participate in proton-driven internal reorganizations involving the coordinated alloxazine moiety, i.e., transformation of an α-iminoketo chelating form to an α-iminoenolato chelating form and the reverse process without any electron-transfer step: Ru^II(acac)₂(L) (<b>1</b>) → Ru^II(acac)₂(L^–) (<b>2</b>^–) and Ru^III(acac)₂(L^–) (<b>2</b>) → Ru^III(acac)₂(L) (<b>1</b>⁺)

Revelation of Varying Coordination Modes and Noninnocence of Deprotonated 2,2′-Bipyridine-3,3′-diol in {Os(bpy)₂} Frameworks

The reaction of 2,2′-bipyridine-3,3′-diol (H₂L) and <i>cis</i>-Os^II(bpy)₂­Cl₂ (bpy = 2,2′-bipyridine) results in isomeric forms of [Os^II(bpy)₂(HL^–)]­ClO₄, [<b>1</b>]­ClO₄ and [<b>2</b>]­ClO₄, because of the varying binding modes of partially deprotonated HL^–. The identities of isomeric [<b>1</b>]­ClO₄ and [<b>2</b>]­ClO₄ have been authenticated by their single crystal X-ray structures. The ambidentate HL^– in [<b>2</b>]­ClO₄ develops the usual N,N bonded five-membered chelate with a strong O–H···O hydrogen bonded situation (O–H···O angle: 160.78°) at its back face. The isomer [<b>1</b>]­ClO₄ however represents the monoanionic O^–,N coordinating mode of HL^–, leading to a six-membered chelate with the moderately strong O–H···N hydrogen bonding interaction (O–H···N angle: 148.87°) at its backbone. The isomeric [<b>1</b>]­ClO₄ and [<b>2</b>]­ClO₄ also exhibit distinctive spectral, electrochemical, electronic structural, and hydrogen bonding features. The p<i>K</i>_a values for [<b>1</b>]­ClO₄ and [<b>2</b>]­ClO₄ have been estimated to be 0.73 and <0.2, respectively, thereby revealing the varying hydrogen bonding interaction profiles of O–H···N and O–H···O involving the coordinated HL^–. The O–H···O group of HL^– in <b>2</b>⁺ remains invariant in the basic region (pH 7–12), while deprotonation of O–H···N group of HL^– in <b>1</b>⁺ estimates the p<i>K</i>_b value of 11.55. This indeed has facilitated the activation of the exposed O–H···N function in [<b>1</b>]­ClO₄ by the second {Os^II(bpy)₂} unit to yield the L^2– bridged [(bpy)₂Os^II(μ-L^2–)­Os^II(bpy)₂]­(ClO₄)₂ ([<b>3</b>]­(ClO₄)₂). However, the O–H···O function in [<b>2</b>]­ClO₄ fails to react with {Os^II(bpy)₂}. The crystal structure of [<b>3</b>]­(ClO₄)₂ establishes the symmetric N,O^–/O^–,N bridging mode of L^2–. On the other hand, the doubly deprotonated L′^2– (H₂L′ = 2,2′-biphenol) generates structurally characterized twisted seven-membered O^–,O^– bonded chelate (torsion angle >50°) in paramagnetic [Os^III(bpy)₂­(L′^2–)]­ClO₄ ([<b>4</b>]­ClO₄). The electronic structural aspects of the complexes reveal the noninnocent potential of the coordinated HL^–, L^2–, and L′^2–. The <i>K</i>_c value of 49 for <b>3</b>³⁺ reveals a class I mixed-valent Os^IIOs^III state

Electronic Structure and Multicatalytic Features of Redox-Active Bis(arylimino)acenaphthene (BIAN)-Derived Ruthenium Complexes

The article examines the newly designed and structurally characterized redox-active BIAN-derived [Ru­(trpy)­(R-BIAN)­Cl]­ClO₄ ([<b>1a</b>]­ClO₄–[<b>1c</b>]­ClO₄), [Ru­(trpy)­(R-BIAN)­(H₂O)]­(ClO₄)₂ ([<b>3a</b>]­(ClO₄)₂–[<b>3c</b>]­(ClO₄)₂), and BIAO-derived [Ru­(trpy)­(BIAO)­Cl]­ClO₄ ([<b>2a</b>]­ClO₄) (trpy = 2,2′:6′,2′′-terpyridine, R-BIAN = bis­(arylimino)­acenaphthene (R = H (<b>1a</b>⁺, <b>3a</b>²⁺), 4-OMe (<b>1b</b>⁺, <b>3b</b>²⁺), 4-NO₂ (<b>1c</b>⁺, <b>3c</b>²⁺), BIAO = [<i>N</i>-(phenyl)­imino]­acenapthenone). The experimental (X-ray, ¹H NMR, spectroelectrochemistry, EPR) and DFT/TD-DFT calculations of <b>1a</b>^<i>n</i>–<b>1c</b>^<i>n</i> or <b>2a</b>^<i>n</i> collectively establish {Ru^II–BIAN⁰} or {Ru^II–BIAO⁰} configuration in the native state, metal-based oxidation to {Ru^III–BIAN⁰} or {Ru^III–BIAO⁰}, and successive electron uptake processes by the α-diimine fragment, followed by trpy and naphthalene π-system of BIAN or BIAO, respectively. The impact of the electron-withdrawing NO₂ function in the BIAN moiety in <b>1c</b>⁺ has been reflected in the five nearby reduction steps within the accessible potential limit of −2 V versus SCE, leading to a fully reduced BIAN^4– state in [<b>1c</b>]^4–. The aqua derivatives ({Ru^II–OH₂}, <b>3a</b>²⁺–<b>3c</b>²⁺) undergo simultaneous 2e^–/2H⁺ transfer to the corresponding {Ru^IVO} state and the catalytic current associated with the Ru^IV/Ru^V response probably implies its involvement in the electrocatalytic water oxidation. The aqua derivatives (<b>3a</b>²⁺–<b>3c</b>²⁺) are efficient and selective precatalysts in transforming a wide variety of alkenes to corresponding epoxides in the presence of PhI­(OAc)₂ as an oxidant in CH₂Cl₂ at 298 K as well as oxidation of primary, secondary, and heterocyclic alcohols with a large substrate scope with H₂O₂ as the stoichiometric oxidant in CH₃CN at 343 K. The involvement of the {Ru^IVO} intermediate as the active catalyst in both the oxidation processes has been ascertained via a sequence of experimental evidence