Noninnocence of the deprotonated 1,2-bis((1<i>H</i>-pyrrol-2-yl)methylene)hydrazine bridge in diruthenium frameworks – a function of co-ligands

Kumari, Meena; Bera, Sudip Kumar; Lahiri, Goutam Kumar

doi:10.1039/d1dt01488a

Cited by 10 publications

(14 citation statements)

References 78 publications

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“…However, oneelectron-oxidized species 3 2+ (S = 1) displayed a metal-based EPR (g ≈ 2.09) at 100 K with a low g anisotropy (Δg = 0.25) value but without the resolution of the forbidden g 1/2 (Δm s = 2) signal, presumably because of the effect of the rapid relaxation process (Figure 6). 33 The lower g anisotropy revealed a minor but not insignificant metal contribution on oxidation (O1), in agreement with a spin density value of 3 2+ (Ru1: 1.095, Ru2: −0.002, and Iz − : 0.681) (Figure S5 and Table S19). Thus, the Scheme 6.…”

Section: ■ Results and Discussionsupporting

confidence: 80%

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

et al. 2022

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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 pK a values of 8.4 and 11.3/10.8, respectively.

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Section: ■ Results and Discussionsupporting

confidence: 80%

“…Synthesis of [(acac) 33 mg;Cu,33.4 mg;and Zn,33.6 mg) in 10 mL of EtOH was then added to the above solution at 298 K, and the solvent was removed under reduced pressure. The solid compound thus obtained in each case was purified on a neutral alumina column using 2:1 n-hexane-CH 2 Cl 2 as an eluent.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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

et al. 2022

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“…The reaction of preformed abbt with the metal precursor ctc -[Ru II (pap) 2 (EtOH) 2 ](ClO 4 ) 2 (EtOH = ethanol) in refluxing EtOH under a dinitrogen atmosphere (pap = strongly π-accepting pap, ctc = cis - trans - cis with respect to the solvent, pyridine, and azo nitrogen atoms of pap, respectively) resulted in the mononuclear complex [Ru II (pap) 2 (abbt •– )]ClO 4 ([ 1 ]ClO 4 ) as an exclusive product (Scheme and Experimental Section). Stabilization of the one-electron-reduced radical anionic form of abbt •– in [ 1 ]ClO 4 was authenticated by its single-crystal X-ray structure (see later).…”

Section: Resultsmentioning

confidence: 99%

“…The precursor complexes ctc -Ru(pap) 2 (EtOH) 2 , cis -Ru(bpy) 2 (EtOH) 2 , and the ligand abbt were prepared according to the literature procedures. Other chemicals and solvents were of reagent-grade and were used as received.…”

Section: Methodsmentioning

confidence: 99%

Radical versus Nonradical States of Azobis(benzothiazole) as a Function of Ancillary Ligands on Selective Ruthenium Platforms

et al. 2021

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The paper deals with the electronic impact of ancillary ligands on the varying redox features of azobis(benzothiazole) (abbt) in the newly introduced mononuclear ruthenium complexes [Ru(pap) 2 (abbt)] n (1 n ) and [Ru(bpy) 2 (abbt)] n (2 n ), where pap = 2phenylazopyridine and bpy = 2,2′-bipyridine. In this regard, the complexes [Ru II (pap) 2 (abbt •− )]ClO 4 ([1]ClO 4 ), [Ru II (pap) 2 (abbt 0 )](ClO 4 ) 2 ([1](ClO 4 ) 2 ), [Ru II (bpy) 2 (abbt 0 )](ClO 4 ) 2 ([2](ClO 4 ) 2 ), and [Ru II (bpy) 2 (abbt •− )]ClO 4 ([2]ClO 4 ) were structurally and spectroscopically characterized. Unambiguous assignments of the aforestated radical and nonradical forms of abbt in 1 + /2 + and 1 2+ /2 2+ , respectively, were made primarily based on their redox-sensitive azo (NN) bond distances as well as by their characteristic electron paramagnetic resonance (EPR)/NMR signatures. Although the radical form of abbt •− was isolated as an exclusive product in the case of strongly π-acidic pap-derived 1 + , the corresponding moderately π-acidic bpy ancillary ligand primarily delivered an oxidized form of abbt 0 in 2 2+ , along with the radical form in 2 + as a minor (<10%) component. The oxidized abbt 0 -derived [1](ClO 4 ) 2 was, however, obtained via the chemical oxidation of [1]ClO 4 . Both 1 + and 2 2+ displayed multiple closed by reversible redox processes (one oxidation O1 and four successive reductions R1−R4) within the potential window of ±2.0 V versus saturated calomel electrode. The involvement of metal-, ligand-, or metal/ligand-based frontier molecular orbitals along the redox chain was assigned based on the combined experimental (structure, EPR, and spectroelectrochemisry) and theoretical [density functional theory (DFT): molecular orbitals, Mulliken spin densities/time-dependent DFT] investigations. It revealed primarily ligand (abbt/pap or bpy)-based redox activities, keeping the metal ion as a simple spectator. Moreover, frontier molecular orbital analysis corroborated the initial isolation of the radical and nonradical species for the pap-derived 1 + and bpy-derived 2 2+ as well as facile reduction of pap and abbt in 1 + and 2 + , respectively.

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“…Unlike π-accepting bpy/pap coligand-derived [ 5 ]ClO 4 –[ 8 ]ClO 4 , the presence of three anionic ligands, i.e., 2acac – + pyS – or 2Cl – + pyS – in 1 or 2 , respectively, facilitated the selective stabilization of the Ru(III) state (μ/B.M. : 1.82 for 1 and 1.81 for 2 , determined by the Evans method; Table S1).…”

Section: Resultsmentioning

confidence: 99%

On the Question of S–S Bond Cleavage of 2,2′-Dithiodipyridine on Selective Ru and Os Platforms. MLCT or Hydride or Solvent Mediated Event

et al. 2022

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This article deals with the S–S bond scission of the model substrate 2,2′-dithiodipyridine (DTDP) in the presence of a selective set of metal precursors: RuII(acac)2, [RuIICl2(PPh3)3], [RuIIHCl(CO)(PPh3)3], [RuII(H)2(CO)(PPh3)3], [RuII(bpy)2Cl2], [RuII(pap)2Cl2], [OsII(bpy)2Cl2], and [OsII(pap)2Cl2] (acac, acetylacetonate; bpy, 2,2′-bipyridine; pap, 2-phenylazopyridine). This led to the eventual formation of the corresponding mononuclear complexes containing the cleaved pyridine-2-thiolate unit in 1–4/[5]ClO4–[8]ClO4. The formation of the complexes was ascertained by their single-crystal X-ray structures, which also established sterically constrained four-membered chelate (average N1–M–S1 angle of 67.89°) originated from the in situ-generated pyridine-2-thiolate unit. Ruthenium(III)-derived one-electron paramagnetic complexes 1–2 (S = 1/2, magnetic moment/B.M. = 1.82 (1)/1.81(2)) exhibited metal-based anisotropic electron paramagnetic resonance (EPR) (Δg: 1/2 = 0.64/0.93, ⟨g⟩: 1/2 = 2.173/2.189) and a broad 1H nuclear magnetic resonance (NMR) signature due to the contact shift effect. The spectroelectrochemical and electronic structural aspects of the complexes were analyzed experimentally in combination with theoretical calculations of density functional theory (DFT and TD-DFT). The unperturbed feature of DTDP even in refluxing ethanol over a period of 10 h can be attributed to the active participation of the metal fragments in facilitating S–S bond cleavage in 1–4/[5]ClO4–[8]ClO4. It also revealed the following three probable pathways toward S–S bond cleavage of DTDP as a function of metal precursors: (i) the metal-to-ligand charge-transfer (MLCT) (RuII → σ* of DTDP)-driven metal oxidation (RuII → RuIII) process in the case of relatively electron-rich metal fragments {RuII(acac)2} or RuIICl2 in 1 or 2, respectively; (ii) metal hydride-assisted formation of 3 or 4 with the concomitant generation of H2; and (iii) S–S bond reduction with the simultaneous oxidation of the solvent benzyl alcohol to benzaldehyde.

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Noninnocence of the deprotonated 1,2-bis((1H-pyrrol-2-yl)methylene)hydrazine bridge in diruthenium frameworks – a function of co-ligands

Cited by 10 publications

References 78 publications

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

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

Radical versus Nonradical States of Azobis(benzothiazole) as a Function of Ancillary Ligands on Selective Ruthenium Platforms

On the Question of S–S Bond Cleavage of 2,2′-Dithiodipyridine on Selective Ru and Os Platforms. MLCT or Hydride or Solvent Mediated Event

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