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

Abstract

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.

Unique Metal–Ligand Interplay in Directing Discrete and Polymeric Derivatives of Isomeric Azole-Carboxylate. Varying Electronic Form, C–C Coupling, and Receptor Feature

“…Accordingly, 1 2+ and 2 2+ ( S = 1/2) displayed metal- and ligand-dominated MSD: Ru/HL1: 0.815/0.186 and Ru/L1: 0.022/0.990, respectively, and the former is attributed to anisotropic EPR . On the other hand, MSD plots suggested a mixed electronic form of {M II -L1 •– /L2 •– } + /{M III -L1 2– /L2 2– )} + (M = Ru/Os) for 3 + , 4 + , 5 + , 8 + , and 9 + ( S = 1/2) and [B 2 Ru 2.5 (μ-L2 2−) Ru 2.5 B 2 ] 3+ /[B 2 Ru II (μ-L2 •−) Ru II B 2 ] 3+ and [B 2 Ru III (μ-L2 2−) Ru III B 2 ] 4+ /[B 2 Ru 2.5 (μ-L2 •– )­Ru 2.5 B 2 ] 4+ for 6 3+ ( S = 1/2) and 6 4+ ( S = 1), respectively (Scheme S1, Supporting Information) due to the impact of metal–ligand covalency . The impact of π-accepting pap in [ 7 ]­(ClO 4 ) 2 was also reflected in the L2′ 2– → L2′ •– oxidation instead of Ru II → Ru III (Scheme S1, Supporting Information) .…”

“…The L1 and L2 derived ruthenium and osmium complexes in Scheme exhibited multiple transitions in the wide spectral range of 1000–200 nm in CH 3 CN with varying intensities, which could be interpreted well via TD-DFT calculations (Figure and Table S54 in the Supporting Information). The analysis of the spectra revealed severe overlapping of metal and L based orbitals in the visible-region-transition processes due to the impact of covalency, and higher energy UV region intense transitions were dominated by the intra/inter-ligand transitions involving electron-rich L and accepting bpy or pap. The spectral profile varied reasonably as a function of metal ions (Ru versus Os), ligands (L1 versus L2), co-ligands (bpy versus pap), as well as their molecular forms (monomer versus dimer).…”

Ruthenium-hydride-mediated stabilisation of the azo anion radical of azobis(benzothiazole) and its reversible electron-reservoir feature

“…The use of a varying ratio of the metal precursor and L, including refluxing in THF or high boiling EtOH/toluene solvent, failed to deliver the corresponding dinuclear species, presumably due to the steric constraint exerted by the bulkier PPh 3 groups under the syn-configured L in 1-3 (vide infra). 10 The isolated complexes 1-3 and corresponding oxidised species [1]ClO 4 -[3]ClO 4 could easily be generated for subsequent structural validation (vide infra).…”

“…S7, ESI †). 9,11 The average trans/cis angles of [1]ClO 4 : 173.00(8)1/90.90(9)1, [2]ClO 4 : 171.84(4)1/91.00(6)1, [3]ClO 4 : 172.96(9)1/90.69 (10)1 a DFT optimised.…”

“…The distances corresponding to Ru-P, Ru-Cl, Ru-CO, and C-O were in good agreement with reported analogous systems. 10,12 One-electron paramagnetic complexes 1-3 (S = 1/2, m eff /B.M. = 1: 1.83, 2: 1.78, 3: 1.86 in CDCl 3 at 77 K, determined by following Evans method, 13 Table S4, ESI †) displayed ill-defined (beyond any meaningful interpretation) 1 H NMR spectral profiles (Fig.…”