Analysis of Redox Series of Unsymmetrical 1,4-Diamido-9,10-anthraquinone-Bridged Diruthenium Compounds

Abstract

The unsymmetrical diruthenium complexes [(bpy)2Ru(II)(μ-H2L(2-))Ru(III)(acac)2]ClO4 ([3]ClO4), [(pap)2RuII(μ-H2L(2-))Ru(III)(acac)2]ClO4 ([4]ClO4), and [(bpy)2Ru(II)(μ-H2L(2-))Ru(II)(pap)2](ClO4)2 ([5](ClO4)2) have been obtained by way of the mononuclear precursors [(bpy)2Ru(II)(H3L(-))]ClO4 ([1]ClO4) and [(pap)2Ru(II)(H3L(-))]ClO4 ([2]ClO4) (where bpy = 2,2′-bipyridine, pap = 2-phenylazopyridine, acac(-) = 2,4-pentanedionate, and H4L = 1,4-diamino-9,10-anthraquinone). Structural characterization by single-crystal X-ray diffraction and magnetic resonance (nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR)) were used to establish the oxidation state situation in each of the isolated materials. Cyclic voltammetry, EPR, and ultraviolet-visible-near-infrared (UV-vis-NIR) spectroelectrochemistry were used to analyze the multielectron transfer series of the potentially class I mixed-valent dinuclear compounds, considering the redox activities of differently coordinated metals, of the noninnocent bridge and of the terminal ligands. Comparison with symmetrical analogues [L2′Ru(μ-H2L)RuL2′](n) (where L′ = bpy, pap, or acac(-)) shows that the redox processes in the unsymmetrical dinuclear compounds are not averaged, with respect to the corresponding symmetrical systems, because of intramolecular charge rearrangements involving the metals, the noninnocent bridge, and the ancillary ligands.

Synthesis, Characterization, and Water Oxidation Activity of Isomeric Ru Complexes

“…Single crystals of the complexes trans - 1 , cis - 1 , and trans - 2 together with the related picolinate derivative cis -[Ru­(trpy)­(pic)­Cl] were obtained, and their ORTEP structures are shown in Figure . All the complexes display the typical slightly distorted octahedral geometry around the ruthenium, as expected for low-spin d 6 Ru II . , The bidentate ligand 8-quinolinecarboxylate occupies both axial and equatorial positions and is bonded to the ruthenium metal via the anionic oxygen atom O1 (carboxylate) and neutral nitrogen atom N1 (quinoline; see Figure for the labeling key) donors forming a six-membered chelate ring. The meridional configuration of trpy introduces an expected geometrical constraint as has been reflected in the NRuN trans angle involving the trpy ligand (for trans - 1 , the N2–Ru–N4 angle is 160.21(17); for trans - 2 , the N2–Ru–N4 angle is 159.26(13)).…”

Catalytic Oxidation of Water to Dioxygen by Mononuclear Ru Complexes Bearing a 2,6‐Pyridinedicarboxylato Ligand

“…It exhibits typical EPR features of unsymmetrical Ru III complexes with g x =2.69, g y =2.42 and g z =2.04 (Figure S5c). The large g anisotropy and the deviation of the average g factor from the free electron value of 2.0023 indicate a significant contribution from the heavy metal with its high spin‐orbit coupling constant to the spin distribution . The Ru III chlorido complex 1 III also shows a characteristic signal of the corresponding unpaired electron, but with a broader signature (Figure S5e) .…”

Unusually Strong Long-range Electronic Coupling Across Redox-Active Bridges in M3+/M4+ Mixed-Valence Complexes of Group 4 Congeners

“…Using the values of ΔE1/2, the comproportionation constants, Kc1 and Kc2, were determined for the one-and two-electron reduced derivatives of TIP Me and complexes 1-3. For all three complexes, the values obtained for Kc1 are larger than expected for complexes of this length, meaning they each have some degree of delocalization; 35,[111][112][113][114] however, the value for complex 1, was several orders of magnitude smaller than those of 2 and 3. This difference indicates that that reduced derivatives of the titanium complex will be significantly less delocalized in comparison to their zirconium and hafnium counterparts.…”

“…[29][30] Overwhelmingly, inorganic/organic hybrid species developed as molecular wires feature so-called redox-active ligands as the bridging species. 5,[31][32][33][34][35] This trend is likely due to noninnocence displayed by these systems, whereby admixing of the ligand frontier orbitals and d-orbitals of the coordinated metal ion yield the requisite electronic delocalization for wire-like behavior, [36][37][38][39][40][41][42] and electronic cooperativity between the metal and ligand can provide additional stability during electron transfer. [43][44][45][46][47] The ligands of choice for these systems largely feature endocyclic imine moieties, such as pyrazine, 5,[48][49][50][51] pyridine, 22,[25][26][52][53][54][55][56] and porphyrin functionalities.…”