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

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 Q0–Q2– of the
noninnocent ligand, the series 22+–20 and 32+–3– retain RuII. 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
RuII(Q0) or RuIII(Q• –).

本研究制备并结构鉴定了含有Q = N,N′-二苯基-邻苯醌二亚胺（Q）和提供2,4-戊二酸酯配体（acac–）、π-受体2,2'-联吡啶（bpy）或强π-受体2-苯基氮杂吡啶（pap）的化合物Ru­(acac)2(Q)（1）、[Ru­(bpy)2(Q)]­(ClO4)2 ([2]­(ClO4)2)和[Ru­(pap)2(Q)]­PF6 ([3]­PF6)。通过实验（电化学、磁共振、紫外-可见-近红外（UV-vis-NIR）光谱电化学）和计算方法（DFT/TD-DFT）研究了这些配合物的电子结构及其可及的氧化和还原形式，揭示了显著可变的电子转移行为和电荷分布。尽管氧化还原系统1+–1–倾向于三价钌以及非中性配体的相应氧化态Q0–Q2–，但系列22+–20和32+–3–则保持RuII。bpy和pap共配体不仅作为旁观者，而且在Q的第二次还原之前还可以被还原。本研究通过新的实验和计算证据，对共配体对金属的影响进行了探讨，这与关于邻苯醌二亚胺配体取代效应的报告[Kalinina等，Inorg. Chem. 2008, 47, 10110]以及关于最合适的氧化态表述RuII(Q0)或RuIII(Q•–)的讨论相辅相成。