1,5-Diamido-9,10-anthraquinone, a Centrosymmetric Redox-Active Bridge with Two Coupled β-Ketiminato Chelate Functions: Symmetric and Asymmetric Diruthenium Complexes

Abstract

The dinuclear complexes {(μ-H2L)[Ru(bpy)2]2}(ClO4)2 ([3](ClO4)2), {(μ-H2L)[Ru(pap)2]2}(ClO4)2 ([4](ClO4)2), and the asymmetric [(bpy)2Ru(μ-H2L)Ru(pap)2](ClO4)2 ([5](ClO4)2) were synthesized via the mononuclear species [Ru(H3L)(bpy)2]ClO4 ([1]ClO4) and [Ru(H3L)(pap)2]ClO4 ([2]ClO4), where H4L is the centrosymmetric 1,5-diamino-9,10-anthraquinone, bpy is 2,2'-bipyridine, and pap is 2-phenylazopyridine. Electrochemistry of the structurally characterized [1]ClO4, [2]ClO4, [3](ClO4)2, [4](ClO4)2, and [5](ClO4)2 reveals multistep oxidation and reduction processes, which were analyzed by electron paramagnetic resonance (EPR) of paramagnetic intermediates and by UV-vis-NIR spectro-electrochemistry. With support by time-dependent density functional theory (DFT) calculations the redox processes could be assigned. Significant results include the dimetal/bridging ligand mixed spin distribution in 3(3+) versus largely bridge-centered spin in 4(3+)-a result of the presence of Ru(II)-stabilizig pap coligands. In addition to the metal/ligand alternative for electron transfer and spin location, the dinuclear systems allow for the observation of ligand/ligand and metal/metal site differentiation within the multistep redox series. DFT-supported EPR and NIR absorption spectroscopy of the latter case revealed class II mixed-valence behavior of the oxidized asymmetric system 5(3+) with about equal contributions from a radical bridge formulation. In comparison to the analogues with the deprotonated 1,4-diaminoanthraquinone isomer the centrosymmetric H2L(2-) bridge shows anodically shifted redox potentials and weaker electronic coupling between the chelate sites.

Hydrogen peroxide assisted photorelease of an anthraquinone-based ligand from [Ru(2,2′-bipyridine)2(9,10-dioxo-9,10-dihydroanthracen-1-olate)]Cl in aqueous solution

“…25 The hard donor oxygen atoms would in addition facilitate stabilization of the Ru 3+ oxidation state, hence perturbing the redox potential at the metal centre. 26 Release of the anthraquinone ligand could also introduce an additional species to perturb the complicated redox chemistry within mitochondria. 27 To these ends, the chirally pure complex RU1 was targeted containing the deprotonated form of 1-hydroxyanthra-9,10-quinone (HAQ).…”

Crystal Structure of (2-Picolinato)bis(2,2′-bipyridine)ruthenium(II) Chloride

“…That is to say, the four O···H-C interactions between two Ru(II) complex cations allow the cations to come close to each other so that the bpy ligands are twisted. Similar O···H-C interactions between two O atoms of a ClO4 -ion and 3,3′-protons of a bpy ligand in {(μ-H2L)[Ru(bpy)2]2}(ClO4)2 (H4L = 1,5-diamino-9,10-anthraquinone) have also been observed, 7 in which the dihedral angles of the bpy ligands (9.9 and 10.4 ) are similar to those in [Ru(pic)(bpy)2](PF6). We thus feel a great interest in the structure of [Ru(pic)(bpy)2] + with another counter anion.…”

Isomeric Diruthenium Complexes Bridged by Deprotonated Indigo in cis and trans Configuration

“…The structural data point to an only partially α‐diimine‐type chelation of Ru1 in 1 with a relatively long central C−C bond while the trans isomer can be best described as containing two ketiminato chelate functions with partial double bond character of the central C−C bond (Scheme ). The bond lengths C1−N1 and C1−C9 in the center do not show much variation (Table ) because the twofold chelation restricts bond stretching movements .…”

“…The calculated lower energy of the broken symmetry singlet BS(1,1) S = 0a s compared to the triplet (S = 1) state for both 1 and 2 ( Table S5 in the Supporting Information) also corroboratesa na ntiferromagnetically coupled situation. The structural data point to an only partially a-diimine-type chelation of Ru1 in 1 with ar elativelyl ong central CÀCb ond [11] while the trans isomer can be best described as containing two ketiminatoc helate functions [12] with partial doubleb ond character of the central CÀCb ond (Scheme 1). The bond lengthsC 1 ÀN1 and C1ÀC9 in the center do not show much variation (Table 2) because the twofold chelation restricts bond stretching movements.…”