Ancillary Ligand Control of Electronic Structure in o-Benzoquinonediimine-Ruthenium Complex Redox Series: Structures, Electron Paramagnetic Resonance (EPR), and Ultraviolet−Visible−Near-Infrared (UV-vis-NIR) Spectroelectrochemistry

Abstract

The compounds Ru(acac)2(Q) (1), [Ru(bpy)2(Q)](ClO4)2 ([2](ClO4)2), and [Ru(pap)2(Q)]PF6 ([3]PF6), containing Q = N,N'-diphenyl-o-benzoquinonediimine and donating 2,4-pentanedionate ligands (acac(-)), π-accepting 2,2(/)-bipyridine (bpy), or strongly π-accepting 2-phenylazopyridine (pap) were prepared and structurally identified. The electronic structures of the complexes and several accessible oxidized and reduced forms were studied experimentally (electrochemistry, magnetic resonance, ultraviolet-visible-near-infrared (UV-vis-NIR) spectroelectrochemistry) and computationally (DFT/TD-DFT) to reveal significantly variable electron transfer behavior and charge distribution. While the redox system 1(+)-1(-) prefers trivalent ruthenium with corresponding oxidation states Q(0)-Q(2-) of the noninnocent ligand, the series 2(2+)-2(0) and 3(2+)-3(-) retain Ru(II). The bpy and pap co-ligands are not only spectators but can also be reduced prior to a second reduction of Q. The present study with new experimental and computational evidence on the influence of co-ligands on the metal is complementary to a report on the substituent effects in o-quinonediimine ligands [Kalinina et al., Inorg. Chem. 2008, 47, 10110] and to the discussion of the most appropriate oxidation state formulation Ru(II)(Q(0)) or Ru(III)(Q(• -)).

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

“…Characteristically,t he NÀN( azo) bond in pap co-ligands of [2] 2 + is about 1.29 ,s uggesting dp(Ru II )t op*(N=N) charge transfer (back boding) in the ground state. [16,17] The RuÀN1 bond in the five-membered chelate rings Ru1-N1-C1- (Figure 2, Table 3, and Figure S5 in the SupportingI nformation). All corresponding features lie at more positive potentials for the pap-containing system with the stronger p-acceptor co-ligand.…”

Redox‐triggered chiroptical switching activity of ruthenium(III)‐bis‐(β‐diketonato) complexes bearing a bipyridine‐helicene ligand

“…[11][12][13][14][15] Hence, the reaction − (denoted as (P,Δ*)- [4] .+ ,PF 6 − in the text) along with the corresponding optimized (BP/SV(P) with continuum solvent model for CH 2 Cl 2 ) molecular structures of [4] .+ and their relative energies, ΔE in kcal mol −1 (see also SI) between 2 and racemic bipyridine-carbo [6]helicene rac-3 in refluxing toluene resulted in the formation of the mononuclear cationic Ru(III) complex [4] .+ ,PF 6 − as a brown precipitate that was obtained in 85% yield after purification over silica gel column chromatography. [11][12][13][14][15] Hence, the reaction − (denoted as (P,Δ*)- [4] .+ ,PF 6 − in the text) along with the corresponding optimized (BP/SV(P) with continuum solvent model for CH 2 Cl 2 ) molecular structures of [4] .+ and their relative energies, ΔE in kcal mol −1 (see also SI) between 2 and racemic bipyridine-carbo [6]helicene rac-3 in refluxing toluene resulted in the formation of the mononuclear cationic Ru(III) complex [4] .+ ,PF 6 − as a brown precipitate that was obtained in 85% yield after purification over silica gel column chromatography.…”

“…The labile CH 3 CN ligands can then be easily replaced, thus allowing to prepare a wide range of stable mixedligand Ru(III) complexes. [11][12][13][14][15] Hence, the reaction between 2 and racemic bipyridine-carbo [6]helicene rac-3 in refluxing toluene resulted in the formation of the mononuclear cationic Ru(III) complex [4] .+ ,PF 6 − as a brown precipitate that was obtained in 85% yield after purification over silica gel column chromatography. The [4] .+ ,PF 6 − compound displayed a broad and unresolved 1 H NMR spectrum, probably due to its paramagnetic and diastereomeric character.…”

“…Herein, we describe the synthesis of stable octahedral Ru(III) complexes ( [4] .+ ,PF 6 − , Scheme 1) bearing a helicenic bipyridine and two tmhd (tmhd: 2,2,6,6-tetramethyl-3,5heptanedionato) ligands. [11][12][13][14] These novel chiral propeller-like systems have been characterized via electrochemistry examinations, UV-vis and ECD spectroscopy, and first-principles calculations. [11][12][13][14] These novel chiral propeller-like systems have been characterized via electrochemistry examinations, UV-vis and ECD spectroscopy, and first-principles calculations.…”

“…Indeed, bipyridines are widely used ligands that can stabilize metal centers through their strong σ-donating and weak π-back-bonding character, 9,10 while π-conjugated electron-rich β-diketonate ions, such as acac (acac: 2,4-pentanedionate) or tmhd, are known to support mixed-ligand Ru complexes, and, due to their non-innocent behavior, can consequently give access to stable compounds with electroactive properties. [11][12][13][14] These novel chiral propeller-like systems have been characterized via electrochemistry examinations, UV-vis and ECD spectroscopy, and first-principles calculations. Spectroelectrochemical studies have demonstrated that the complexes reveal an efficient redox-triggered chiroptical switching, thus yielding a new example of organometallic helicene-based switch.…”