Diradicals

Abe, Manabu

doi:10.1021/cr400056a

Cited by 1,222 publications

(1,093 citation statements)

References 492 publications

(500 reference statements)

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“…A plot of I×T vs. T shows that I×T decreases upon lowering the temperature ( Figure S4). This behaviour is indicative of a singlet diradical ground state, [19] thus corroborating our computational results. Although singlet biradical species like 4 are rare, Roesky and co-workers recently reported a dicarbene zinc compound for which the singlet diradical was calculated to be lower in energy than the triplet by ~ 4 kcal/mol.…”

supporting

confidence: 89%

“…The presence of an additional electron in both ligands (L 2-) is evidenced by the similar bond lengths in 4b, which are elongated in comparison to the neutral precursor 2b (Table 2). EPR spectra of diradicals [19] 4a and 4b in frozen THF solution (77K) are very similar and show features indicative of randomly oriented triplets (g = 2.0028) with characteristic half-field (Δm s = 2) signals ( Figure 5). The zero-field splitting parameters D = 11.6 × 10 -3 and 11.5 × 10 -3 cm -1 from the EPR spectra for 4a and 4b, respectively, are somewhat smaller than those in the neutral triplet diazabutadiene complex [ t Bu 2 DAB] 2 Zn (23.1 × 10 -3 cm -1 ), [20] and comparable to D-values found for purely organic phenylene-linked bis(radical) compounds (radical = semiquinone; [21] verdazyl), [22] which range between ca.…”

mentioning

confidence: 93%

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The Formazanate Ligand as an Electron Reservoir: Bis(Formazanate) Zinc Complexes Isolated in Three Redox States

et al. 2014

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Metal-mediated redox processes are of fundamental importance in a wide variety of bond formation and cleavage reactions. The utility of transition metal catalysts in this type of reactions stems from their ability to switch between two (or more) oxidation states. Recently, there has been increased interest in redox processes that do not occur at the metal centre, but instead take place within the ancillary ligand framework (so-called 'redox-active' or 'non-innocent' ligands). [1] The use of organic ligands as redox equivalents is of key importance in biological (enzymatic) transformations, [2] and has been shown to open new reactivity pathways in catalysis. [1c] The most studied ligands of this class are dithiolenes and dioxolenes, while recent work has focussed on α-diimines [3] and bis(imino)pyridines. [4] A class of ligands that has found widespread utility in the synthesis of metal complexes across the periodic table are the monoanionic β-diketiminates. [5] These are generally considered as stable ligand scaffolds without involvement in redox-chemistry. Recently, examples of β-diketiminate metal complexes were reported in which the ligand was either reduced to a metal-bound di-or trianion, [6] or oxidized to a neutral radical species. [7] However, the limited stability of β-diketiminate complexes upon changing oxidation state prevents widespread application. [8] Formazanates (1,2,4,5-tetraazapentadienyls), [9] which are close analogues of β-diketiminates, have received comparatively little attention as ligands in coordination chemistry. [10] The stability of organic 6-membered heterocyclic radicals (verdazyls) that are derived from formazans prompted us to explore the use of formazanates as potential redox-active ligands (Chart 1). Here we show that zinc complexes with formazanate ligands engage in remarkably facile and reversible redox-chemistry which allows the full characterization of bis(formazanate) L 2 Zn complexes in charge neutral, anionic or dianionic redox states.

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confidence: 89%

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confidence: 93%

The Formazanate Ligand as an Electron Reservoir: Bis(Formazanate) Zinc Complexes Isolated in Three Redox States

et al. 2014

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“…[53] The two doxyl radicals, 5-and 16-doxylstearic acids (5-and 16-DSA,Sigma) were used as spin probes. The 5-and 16-DSA (10 À2 M) probes in ethanol were added to 200 mL of the membrane suspensions (final concentrations ranged from 3 Â 10 À5 to 10 À4 M) and incubated for 30 min.…”

Section: Electron Spin Resonance (Esr) Studiesmentioning

confidence: 99%

Effects of Different Phases of Cigarette Smoke on Lipid Peroxidation and Membrane Structure in Liposomes

et al. 2014

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This paper discloses for the first time the effects of the gas phase (GP) and the tar of cigarette smoke on lipid peroxidation (LPO) and on the structure of different lipid regions in liposomes. The LPO development was analysed in terms of the total unsaturation of lipids (double-bond, DB, content) and the formation of dienic conjugates (DC), ketodienes (KD), and malonic dialdehyde (MDA). As expected, the exposure of liposomes to either the GP or the tar led to a significant decrease in the DB content. However, the formation of oxidation products revealed different dynamics: MDA generation was inhibited, while the formation of DC and KD increased during the first few hours of the LPO development followed by its inhibition. The smoke constituents exhibited opposite effects on the structure of the lipid bilayer of liposomes: the GP markedly enhanced the microviscosity of liposomal membranes, whereas the tar caused a drastic lowering of microviscosity.

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“…While not intended to provide a comprehensive review on other metal-ligand radical complexes that do not exhibit slow magnetic relaxation, this article will nevertheless briefly survey classes of molecules that could potentially be exploited to realize new, metal-radical ligand singlemolecule magnets. For a more comprehensive account of other metal-radical ligand complexes, the reader is referred to broader and more inclusive review articles [9][10][11][12][13][14][15][16][17][18][19][20][21]. For the latest advances on single-molecule magnets, the reader is referred to some recent review articles [22][23][24][25][26][27][28][29][30].…”

Section: General Introductionmentioning

confidence: 99%