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

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

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

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

Metal–Metal Bridging Using the DPPP Dye System: Electronic Configurations within Multiple Redox Series

Redox series [L_<i>n</i>Ru­(μ-DPPP)­RuL_<i>n</i>]^<i>k</i>, H₂DPPP = 2,5-dihydro-3,6-di-2-pyridylpyrrolo­(3,4-<i>c</i>)­pyrrole-1,4-dione and L = 2,4-pentanedionato (acac^–), 2,2′-bipyridine (bpy), and 2-phenylazopyridine (pap), have been studied by voltammetry (CV, DPV), EPR, and UV–vis–NIR spectroelectrochemistry, supported by TD-DFT calculations. Crystal structure analysis and ¹H NMR revealed oxidation states [(acac)₂Ru^III(μ-DPPP^2–)­Ru^III(acac)₂] and [(bpy)₂Ru^II(μ-DPPP^2–)­Ru^II(bpy)₂]²⁺ for the corresponding precursors, isolated as <i>rac</i> diastereomers. Oxidation was observed to occur mainly at the bridging ligand (DPPP^2– → DPPP^•–), whereas the site of reduction (DPPP, Ru, or L) depends on effects from the ancillary ligands L. The metal coordination of a derivative of the pigment forming 2,5-dihydro-pyrrolo­(3,4-<i>c</i>)­pyrrole-1,4-dione (DPP) dyes and the analysis of corresponding multistep redox series add to the previously recognized coordinative and electron transfer potential of dye molecules of the azo, indigo, anthraquinone, and formazanate type

Tunable Electrochemical and Catalytic Features of BIAN- and BIAO-Derived Ruthenium Complexes

This article deals with a class of ruthenium–BIAN-derived complexes, [Ru^II(tpm)­(R-BIAN)­Cl]­ClO₄ (tpm = tris­(1-pyrazolyl)­methane, R-BIAN = bis­(arylimino)­acenaphthene, R = 4-OMe ([<b>1a</b>]­ClO₄), 4-F ([<b>1b</b>]­ClO₄), 4-Cl ([<b>1c</b>]­ClO₄), 4-NO₂ ([<b>1d</b>]­ClO₄)) and [Ru^II(tpm)­(OMe-BIAN)­H₂O]²⁺ ([<b>3a</b>]­(ClO₄)₂). The R-BIAN framework with R = H, however, leads to the selective formation of partially hydrolyzed BIAO ([<i>N</i>-(phenyl)­imino]­acenapthenone)-derived complex [Ru^II(tpm)­(BIAO)­Cl]­ClO₄ ([<b>2</b>]­ClO₄). The redox-sensitive bond parameters involving NC–CN or NC–CO of BIAN or BIAO in the crystals of representative [<b>1a</b>]­ClO₄, [<b>3a</b>]­(PF₆)₂, or [<b>2</b>]­ClO₄ establish its unreduced form. The chloro derivatives <b>1a</b>⁺–<b>1d</b>⁺ and <b>2</b>⁺ exhibit one oxidation and successive reduction processes in CH₃CN within the potential limit of ±2.0 V versus SCE, and the redox potentials follow the order <b>1a</b>⁺ < <b>1b</b>⁺ < <b>1c</b>⁺ < <b>1d</b>⁺ ≈ <b>2</b>⁺. The electronic structural aspects of <b>1a</b>^<i>n</i>–<b>1d</b>^<i>n</i> and <b>2</b>^<i>n</i> (<i>n</i> = +2, +1, 0, −1, −2, −3) have been assessed by UV–vis and EPR spectroelectrochemistry, DFT-calculated MO compositions, and Mulliken spin density distributions in paramagnetic intermediate states which reveal metal-based (Ru^II → Ru^III) oxidation and primarily BIAN- or BIAO-based successive reduction processes. The aqua complex <b>3a</b>²⁺ undergoes two proton-coupled redox processes at 0.56 and 0.85 V versus SCE in phosphate buffer (pH 7) corresponding to {Ru^II–H₂O}/{Ru^III–OH} and {Ru^III–OH}/{Ru^IVO}, respectively. The chloro (<b>1a</b>⁺–<b>1d</b>⁺) and aqua (<b>3a</b>²⁺) derivatives are found to be equally active in functioning as efficient precatalysts toward the epoxidation of a wide variety of alkenes in the presence of PhI­(OAc)₂ as oxidant in CH₂Cl₂ at 298 K, though the analogous <b>2</b>⁺ remains virtually inactive. The detailed experimental analysis with the representative precatalyst <b>1a</b>⁺ suggests the involvement of the active {Ru^IVO} species in the catalytic cycle, and the reaction proceeds through the radical mechanism, as also supported by the DFT calculations

Tunable Electrochemical and Catalytic Features of BIAN- and BIAO-Derived Ruthenium Complexes

This article deals with a class of ruthenium–BIAN-derived complexes, [Ru^II(tpm)­(R-BIAN)­Cl]­ClO₄ (tpm = tris­(1-pyrazolyl)­methane, R-BIAN = bis­(arylimino)­acenaphthene, R = 4-OMe ([<b>1a</b>]­ClO₄), 4-F ([<b>1b</b>]­ClO₄), 4-Cl ([<b>1c</b>]­ClO₄), 4-NO₂ ([<b>1d</b>]­ClO₄)) and [Ru^II(tpm)­(OMe-BIAN)­H₂O]²⁺ ([<b>3a</b>]­(ClO₄)₂). The R-BIAN framework with R = H, however, leads to the selective formation of partially hydrolyzed BIAO ([<i>N</i>-(phenyl)­imino]­acenapthenone)-derived complex [Ru^II(tpm)­(BIAO)­Cl]­ClO₄ ([<b>2</b>]­ClO₄). The redox-sensitive bond parameters involving NC–CN or NC–CO of BIAN or BIAO in the crystals of representative [<b>1a</b>]­ClO₄, [<b>3a</b>]­(PF₆)₂, or [<b>2</b>]­ClO₄ establish its unreduced form. The chloro derivatives <b>1a</b>⁺–<b>1d</b>⁺ and <b>2</b>⁺ exhibit one oxidation and successive reduction processes in CH₃CN within the potential limit of ±2.0 V versus SCE, and the redox potentials follow the order <b>1a</b>⁺ < <b>1b</b>⁺ < <b>1c</b>⁺ < <b>1d</b>⁺ ≈ <b>2</b>⁺. The electronic structural aspects of <b>1a</b>^<i>n</i>–<b>1d</b>^<i>n</i> and <b>2</b>^<i>n</i> (<i>n</i> = +2, +1, 0, −1, −2, −3) have been assessed by UV–vis and EPR spectroelectrochemistry, DFT-calculated MO compositions, and Mulliken spin density distributions in paramagnetic intermediate states which reveal metal-based (Ru^II → Ru^III) oxidation and primarily BIAN- or BIAO-based successive reduction processes. The aqua complex <b>3a</b>²⁺ undergoes two proton-coupled redox processes at 0.56 and 0.85 V versus SCE in phosphate buffer (pH 7) corresponding to {Ru^II–H₂O}/{Ru^III–OH} and {Ru^III–OH}/{Ru^IVO}, respectively. The chloro (<b>1a</b>⁺–<b>1d</b>⁺) and aqua (<b>3a</b>²⁺) derivatives are found to be equally active in functioning as efficient precatalysts toward the epoxidation of a wide variety of alkenes in the presence of PhI­(OAc)₂ as oxidant in CH₂Cl₂ at 298 K, though the analogous <b>2</b>⁺ remains virtually inactive. The detailed experimental analysis with the representative precatalyst <b>1a</b>⁺ suggests the involvement of the active {Ru^IVO} species in the catalytic cycle, and the reaction proceeds through the radical mechanism, as also supported by the DFT calculations