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The doubly deprotonated bridging ligand L12- derived from 2,6-bis(2-pyridyl)-1,5-dihydro-1’,4’-benzoquinono[2’,3’-d:5’,6’-d’]diimidazole H2L1 forms coordination compounds with two bis(2,2’-bipyridine)osmium(II) complex fragments in anti ([1](ClO4)2) and syn configuration ([2](ClO4)2) of {(μ-L1)[Os(bpy)2]2}(ClO4)2, as evident from...

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.

This article demonstrates the stabilization of ground-and redoxinduced metal-to-ligand charge transfer excited states on coordination of azocoupled bmpd(L4) [bmpd = (E)-1,2-bis(1-methyl-1H-pyrazol-3-yl)diazene; L4 = −N�N−] to the electron-rich {Ru(acac) 2 } (acac = acetylacetonate) unit in mononuclear Ru II (acac) 2 (L4) (1) and diastereomeric dinuclear (acac) 2 Ru 2.5 (μ-L4 •− )Ru 2.5 (acac) 2 [rac, ΔΔ/ΛΛ (2a)/meso, ΔΛ (2b)] complexes, respectively. It also develops further one-step intramolecular electron transfer induced L4On the contrary, under identical reaction conditions electronically and sterically permuted bimpd [L5, (E)-1,2-bis(4-iodo-1-methyl-1H-pyrazol-3-yl)diazene)] delivered mononuclear Ru II (acac) 2 (L5) (3) as an exclusive product. Further, the generation of unprecedented heterotrinuclear complex [(acac) 2 Ru II (μ-L4)Ag I (μ-L4)Ru II (acac) 2 ]ClO 4 ([4]ClO 4 ) involving unreduced L4 via the reaction of 1 and AgClO 4 revealed the absence of any inner-sphere electron transfer (IET) as in precursor 1, which in turn reaffirmed an IET (at the interface of electron-rich Ru(acac) 2 and acceptor L4) mediated stabilization of 2. Structural authentication of the complexes with special reference to the tunable azo distance (N�N, N−N •− , N−N 2− ) of L and their spectro-electrochemical events in accessible redox states including the reversible electron reservoir feature of 2 → 2 + /2 + → 2 were evaluated in conjunction with density functional theory/time-dependent density functional theory calculations. The varying extent of IET as a function of heteroaromatics appended to the azo group of L (L1 = abpy = 2,2′-azobipyridine, L2 = abbt = 2,2′-azobis(benzothiazole), L3 = abim = azobis(1-methylbenzimidazole), L4 and L5, Schemes 1 & 2) in the Ru(acac) 2 -derived respective molecular setup has been addressed.

Redox driven C-C bond formation has gained recent attention over the traditional sequence of oxidative addition, insertion and reductive elimination. In this regard, transient radical mediated diverse reactivity profile of...

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Facile reduction of 2,2-dithiobisbenzothiazole by the mediation of metal-to-ligand charge transfer or by internal reducing equivalent was demonstrated. It led to varying binding modes of thiolates (1, 2, ) in...