The Indigo Isomer Epindolidione as a Redox‐Active Bridging Ligand for Diruthenium Complexes

Abstract

Epindolidione (H 2 L), ah eteroatom-modifieda nalogue of tetracene and as tructural isomer of indigo, forms dinuclear complexesw ith [RuX 2 ] 2 + ,X = bpy (2,2'-bipyridine, [1] 2 +)o rpap (2-phenylazopyridine, [2] 2 +), in its doubly deprotonatedb ridging form m-L 2À .The dications in compounds meso-[1](ClO 4) 2 and meso-[2](ClO 4) 2 ,[ X 2 Ru(m-L)RuX 2 ](ClO 4) 2 , contain five-membered chelate rings N-CÀC-O-Ru II with p bridged metalsa ta ni ntramolecular distance of 7.19 .S tepwise reversible oxidation and reduction is mainly ligand centered (oxidation:L 2À ;r eduction:X), as deduced from EPR of one-electron oxidized and reduced intermediates and from UV/Vis/NIR spectroelectrochemistry,s upported by TD-DFT calculation results.T he results for [1](ClO 4) 2 and [2](ClO 4) 2 are qualitatively similart ot he ones observed with the deprotonated indigo-bridged isomers with their six-membered chelate ring structures, confirming the suitability of both p systems for molecular electronicsa pplications, low-energy absorptions, and multiple electron transfers. Scheme1.Structuralisomers of indigo and epindolidione. Scheme2.The two diruthenium complexes [1](ClO 4) 2 and [2](ClO 4) 2 with doublydeprotonated epindolidione presented in this work.

Bidirectional noninnocence of hinge-like deprotonated bis-lawsone on selective ruthenium platform: a function of varying ancillary ligands

“…The analogous L 2− -bridged paramagnetic (S = 1) diruthenium(III) complex [(acac) 2 Ru III (µ-L 2− )Ru III (acac) 2 ] (2, acac = acetylacetonate) was synthesised from the reaction of Ru (acac) 2 (CH 3 CN) 2 and H 2 L in refluxing THF, in the presence of NEt 3 base under atmospheric conditions. Alternatively, the same reaction of H 2 L with the in situ-generated ctc-[Ru ( pap) 2 (EtOH) 2 ] 2+ ( pap = 2-phenylazopyridine, ctc = cis-trans-cis configuration with respect to EtOH, pyridine, and azo nitrogen donors of pap, respectively 13 ) and NEt 3 in refluxing EtOH under a nitrogen atmosphere selectively resulted in a monomeric complex, Ru II ( pap) 2 (L 2− ) 3 (S = 0, pap = 2-phenylazopyridine) (see Experimental section, Scheme 2). Attempts to achieve the corresponding L 2− -bridged dimeric product, i.e., [( pap) 2 M II (µ-L 2− )M II ( pap) 2 ] 2+ , as in the case of the bpy or acac ancillary ligand, failed even using varying M : H 2 L ratios, extended reaction times and different bases such as NaOH and Na-acetate.…”

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

“…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).…”

“…The solvent was removed under reduced pressure, and the residue was moistened with a few drops of CH 3 CN, followed by the addition of a saturated aqueous solution of NaClO 4 , and then allowed to settle at 273 K. 7.12 (t, J = 6.8 Hz, 1H), 6.95 (t, J = 3.9 Hz, 1H), 6.81 (d, J = 4.7 Hz, 1H), 6.60 (t, J = 6.1 Hz, 1H) ppm. 13 [6]ClO 4 . A mixture of ctc-Ru(pap) 2 Cl 2 •2H 2 O (100 mg, 0.19 mmol) and AgClO 4 (80.00 mg, 0.38 mmol) was heated at reflux for 2 h in 20 mL of EtOH.…”

Osmium(II)-Coordination Induced C–C Bond Functionalization of Bis-lawsone

“…Although isomeric cc - 2 and tc - 3 exhibited almost identical oxidation potentials (O1, 1.1 V; Figure a), an appreciable difference in the potential appeared for the corresponding reduction steps (R1–R3 in Figure a). The correspondences of successive closes by quasi-reversible one-electron reduction to the ancillary ligand (diimine, bpy or NN, pap) could be rationalized by the molecular orbital (MO) compositions and Mulliken spin density at the paramagnetic intermediates (Figures c and S12 and Tables S8–S17) and also ascertained by the free-radical electron paramagnetic resonance (EPR; g = 1.990; Figure b) of the first reduced state of representative 2 – ( S = 1 / 2 ) …”

“…Although isomeric cc-2 and tc-3 exhibited almost identical oxidation potentials (O1, 1.1 V; Figure 2a), an appreciable difference in the potential appeared for the corresponding reduction steps (R1−R3 in Figure 2a). The correspondences of successive closes by quasi-reversible one-electron reduction to the ancillary ligand (diimine, bpy or NN, pap) 15 1.990; Figure 2b) of the first reduced state of representative 2 − (S = 1 / 2 ). 16 1 or 2/3 exhibited one reversible or quasi-reversible oxidation couple (O1), respectively.…”