Crystalline and molecular structure of quinone ?-complexes

Александров, Г. Г.; Struchkov, Yu. T.; Kalinin, Denis; Neigauz, M. G.

doi:10.1007/bf00744342

Cited by 4 publications

(5 citation statements)

References 6 publications

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“…The solvent reorganization energy λ s is known to vary depending on the distance between an electron donor and an acceptor as given by eq 8, where r 1 and r 2 are the radii of the reactants, r 12 is the reaction distance, ε is the dielectric constant, and n is the refractive index. , The RU and DQ radii were reported as crystal structures, and according to those results, the radii were 13 Å and 6.8 Å, respectively. If the reaction distance is assumed as infinite, the term −1/2 r 12 in eq 8 is negligible.…”

Section: Resultsmentioning

confidence: 99%

Does Bimolecular Charge Recombination in Highly Exergonic Electron Transfer Afford the Triplet Excited State or the Ground State of a Photosensitizer?

et al. 2008

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The investigations were made on photoinduced electron transfer (ET) from the singlet excited state of rubrene (1RU*) to p-benzoquinone derivatives (duroquinone, 2,5-dimethyl-p-benzoquinone, p-benzoquinone, 2,5-dichloro-p-benzoquinone, and p-chloranil) in benzonitrile (PhCN) by using the steady state and time-resolved spectroscopies. The photoinduced ET produces solvent-separated type charge-separated (CS) species and the charge-recombination (CR) process between RU radical cation and semiquinone radical anions obeys second-order kinetics. Not only the CS species but also the triplet excited state of RU (3RU*) is seen in the transient absorption spectra upon laser excitation of a PhCN solution of RU and p-benzoquinone derivatives. The comparison of their time profiles clearly suggests that the CR process between RU radical cation and semiquinone radical anions to the ground state is independent from the deactivation of 3RU*. This indicates that the CR in a highly exergonic ET occurs at a longer distance with a large solvent reorganization energy, which results in faster ET to the ground state than to the triplet excited state that is lower in energy than the CS state. Photoinduced ET from 3RU* in addition from 1RU* also occurs when p-benzoquinone derivatives with electron-withdrawing substituents were employed as electron acceptors.

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Section: Resultsmentioning

confidence: 99%

Does Bimolecular Charge Recombination in Highly Exergonic Electron Transfer Afford the Triplet Excited State or the Ground State of a Photosensitizer?

et al. 2008

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“…Quinones ( Q ) are ubiquitous in nature owing to their propensity to form various odd-electron intermediates in different types of biochemical (energy) processes. , Although a wide number of quinones are indeed known and precisely identified by X-ray crystallographic analysis, there is a singular dearth of precise structural and spectroscopic information about the pure quinone anion radical ( Q - • ) itself as the corresponding one-electron reduction product . No doubt, a large part of the difficulty resides in the tenuous effects of the counterion in ion pairing, especially as the associated cation modulates the local structure, the electronic transition, and the stability/reactivity of such an anionic entity. , In this regard, the numerous computational studies of reduced quinones that are extant 7-9 must be recognized relative to the much needed experimental reference points for ion-pairing effects.…”

Section: Introductionmentioning

confidence: 99%

Quinones as Electron Acceptors. X-Ray Structures, Spectral (EPR, UV−vis) Characteristics and Electron-Transfer Reactivities of Their Reduced Anion Radicals as Separated vs Contact Ion Pairs

Rosokha

Neretin

et al. 2006

J. Am. Chem. Soc.

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Successful isolation of a series of pure (crystalline) salts of labile quinone anion radicals suitable for X-ray crystallographic analysis allows for the first time their rigorous structural distinction as "separated" ion pairs (SIPs) vs "contact" ion pairs (CIPs). The quantitative evaluation of the precise changes in the geometries of these quinones (Q) upon one-electron reduction to afford the anion radical (Q-*) is viewed relative to the corresponding (two-electron) reduction to the hydroquinone (H2Q) via the Pauling bond-length/bond-order paradigm. Structural consequences between such separated and contact ion pairs as defined in the solid state with those extant in solution are explored in the context of their spectral (EPR, UV-vis) properties and isomerization of tightly bound CIPs. Moreover, the SIP/CIP dichotomy is also examined in intermolecular interactions for rapid (self-exchange) electron transfer between Q-* and Q with second-order rate constants of kET approximately equal to 10(8) M-1 s-1, together with the spectral observation of the paramagnetic intermediates [Q,Q-*]leading to 1:1 adducts, as established by X-ray crystallography.

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“…The coordinated QC ligands in 1a , 2d , and 3a feature a cyclohexadienone moiety similar to that of related quinones, as revealed by comparison with the X-ray crystal structures of two di( tert -butyl)-substituted 1,4-benzoquinones (Figure , insets A and B). The quinoid structures of the QCs in 1a , 2d , and 3a contrast with the benzenoid structure in the zwitterionic Ru–aryl counterpart of the ruthenaquinone (Figure , inset C) .…”

Section: Resultsmentioning

confidence: 72%

“…Bond distances (Å) for the Ru–QC moieties in the crystal structures of (a) 1a ·AcOEt, (b) 2d ·MeOH, and (c) 3a · n BuOCH 2 CH 2 OH. Insets: Bond distances (Å) in the X-ray crystal structures of two related quinones (A and B; standard errors not available for A; only the average CO, CC, CC distances are reported for B) and selected bond distances (Å) in the X-ray crystal structures of the zwitterionic form of the ruthenaquinone (C) and [Ru(TPFPP)(C(Ph)CO 2 Et)(MeOH)] (D).…”

Section: Resultsmentioning

confidence: 99%

Ruthenium(II) Porphyrin Quinoid Carbene Complexes: Synthesis, Crystal Structure, and Reactivity toward Carbene Transfer and Hydrogen Atom Transfer Reactions

Wang

Wan

et al. 2019

J. Am. Chem. Soc.

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Reactivity study of novel metal carbene complexes can offer new opportunities in catalytic carbene transfer reactions as well as in other synthetic protocols. Metal complexes with quinoid carbene (QC) ligands are assumed to be key intermediates in a variety of metal-catalyzed QC transfer reactions using diazo quinones, which demands development of the chemistry of QC transfer of well characterized metal–QC complexes. Herein we report the isolation and QC transfer of ruthenium porphyrins [Ru(Por)(QC)] which contribute the first examples of (i) structurally characterized metal–QC complex (by X-ray crystallography) and (ii) isolated metal–QC complex that undergoes QC transfer reaction. The complexes [Ru(Por)(QC)] were prepared from reaction of [Ru(Por)(CO)] with diazo quinones and exhibited dual reactivity, i.e., hydrogen atom transfer (HAT) as well as QC transfer. The stoichiometric QC transfer reactions from these Ru–QC complexes to nitrosoarenes (ArNO) afforded nitrones in up to 90% yield, and the corresponding catalytic reactions were also developed. Both the stoichiometric and catalytic reactions for a series of QC ligands bearing electron-donating and -withdrawing substituents showed a reverse substituent effect on the QC transfer reactivity. Complexes [Ru(Por)(QC)] are also reactive toward C–H and X–H (X = N, S) bonds and can catalyze aerobic oxidation of 1,4-cyclohexadiene; their stoichiometric HAT reactions with unsaturated hydrocarbons gave product yields of up to 88%. The unique dual reactivity and electronic feature of [Ru(Por)(QC)] were studied by spectroscopic means and density functional theory (DFT) calculations.

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Crystalline and molecular structure of quinone ?-complexes

Cited by 4 publications

References 6 publications

Does Bimolecular Charge Recombination in Highly Exergonic Electron Transfer Afford the Triplet Excited State or the Ground State of a Photosensitizer?

Does Bimolecular Charge Recombination in Highly Exergonic Electron Transfer Afford the Triplet Excited State or the Ground State of a Photosensitizer?

Quinones as Electron Acceptors. X-Ray Structures, Spectral (EPR, UV−vis) Characteristics and Electron-Transfer Reactivities of Their Reduced Anion Radicals as Separated vs Contact Ion Pairs

Ruthenium(II) Porphyrin Quinoid Carbene Complexes: Synthesis, Crystal Structure, and Reactivity toward Carbene Transfer and Hydrogen Atom Transfer Reactions

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