Ligand field-actuated redox-activity of acetylacetonate

Vinum, Morten G.; Voigt, Laura; Hansen, Steen Honoré; Bell, Colby; Clark, Kensha Marie; Larsen, R. Wugt; Pedersen, Kasper S.

doi:10.1039/d0sc01836h

Cited by 13 publications

(13 citation statements)

References 48 publications

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“…Thus, a strongly paramagnetic state hs -Co II (SQ • ) 2 , i.e., a high-spin ( hs ) Co(II) ion with two semiquinonate(1−) π-radicals (SQ • ), is stabilized in a weak-field five-coordinate complex, whereas a weakly paramagnetic state ls -Co III (SQ • )(Cat), i.e., a diamagnetic low-spin ( ls ) Co(III) ion with one ligand π-radical and one fully reduced catecholate(2−) ligand (Cat), becomes stabilized in a strong-field six-coordinate complex. Ultimately, the addition of a free ligand to a complex solution triggers the hs- Co II (SQ • ) 2 → ls -Co III (SQ • )(Cat) transition. , Similar observations were later made by others on metal complexes featuring other types of redox-active ligands. , …”

Section: Introductionsupporting

confidence: 65%

Molecular Valence Tautomeric Metal Complexes for Chemosensing

et al. 2021

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Switchable valence tautomeric metal complexes have been long suggested for applications as chemosensors. However, no such molecular sensors have been yet reported. Here, we present a concept for sensing and the first prototype molecular sensor based on valence tautomeric cobalt-dioxolenes. A valence tautomeric cobalt-dioxolene complex [ls-CoIII(SQ•)(Cat)(stypy)2] ⇄ [hs-CoII(SQ•)2(stypy)2] 1 (ls = low spin, hs = high spin, Cat = 3,5-di-tert-butylcatecholate(2−), SQ = one-electron oxidized, benzosemiquinone(1−) form of Cat, stypy = trans-4-styrylpyridine) has been used as a molecular sensor. The lability of axial stypy ligands of 1 in solution allows us to exchange stypy ligands by dimethyl sulfoxide and simple pyridine analytes in a controllable way, which triggers colorimetric and magnetic responses.

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Section: Introductionsupporting

confidence: 65%

Molecular Valence Tautomeric Metal Complexes for Chemosensing

et al. 2021

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“…The origin of this huge difference in bond energies will require further investigation but may be linked to the very different coordination environment at the Fe III where now the ligands are weak field, high electronegativity donors (oxygen). It is also interesting to note that the acac ligand is redox active …”

Section: Resultsmentioning

confidence: 99%

Systematic Trends in the Electrochemical Properties of Transition Metal Hydride Complexes Discovered by Using the Ligand Acidity Constant Equation

2020

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Understanding the thermodynamics of paramagnetic transition metal hydride complexes, especially of the abundant 3d metals, is important in the design of electrocatalysts and organometallic catalysts. The pK a MeCN([MHLn]+/[MLn) of paramagnetic hydrides in MeCN are estimated for the first time using the ligand acidity constant (LAC) equation where contributions to the pK a MeCN from each ligand are simply added together, with the sum corrected for effects of charge and 5d metals. The pK a LAC–MeCN([MHLn]+/MLn) of over 200 hydride complexes MHLn are used, along with their electrochemical potentials from the literature, in an uncommonly applied thermochemical cycle in order to reveal systematic trends in the redox couples MIII/II and MV/IV (M = Cr, Mo, W), MnII/I, ReVI/V and ReIV/III, MIII/II and MIV/III (M = Fe, Ru, Os), and MIII/II and MII/I (M = Co, Rh, and Ir) and allow the estimation of the bond dissociation free energies BDFE(MH) of the unoxidized hydrides MHLn and the prediction of the electrochemical potential for their oxidation. Density functional theory (DFT) calculations are used to validate the pK a LAC–MeCN values of hydrides of WIII, MnII, FeIII, RuIII, CoII, and NiIII. When a pK a LAC–MeCN is less than zero for a given complex [MHLn]+, the oxidation of MHLn is irreversible due to proton loss from the oxidized complex to the solvent. When pK a LAC–MeCN ≫ 0, the oxidation is reversible when there is no gross change in the coordination geometry upon a change in the redox state. Twenty paramagnetic hydrides prepared in bulk all have pK a LAC–MeCN > 8.

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“…Two mechanisms to make the π* orbitals the LUMOs have been demonstrated in extant examples: (i) substituents with extended π systems that can accommodate additional electrons 23,26,29,30,32,33 or (ii) additional ligands that force a change in coordination number and drive metal orbital energies below those of ligand LUMOs and facilitate ligand reduction. 21,22 Herein, we report a third and potentially more general approach. When the donor atoms are S, and not O or N, the π* orbitals are lower in energy 91 and sufficiently so as to accept electrons, as we have now observed in the {Pt(cta) 2 } system.…”

Section: ■ Discussionmentioning

confidence: 99%

“…As with five-membered chelate rings, a variety of p -block elements as donor atoms are known. With O-donors, (a) [Cr(hfac) 2 (pyz) 2 ] contains Cr(III), a dianionic radical hexafluoroacetylacetonate (hfac) and pyrazine ligands , whereas (b) has two 9-oxidophenalenone ligands which, analogous to quinones, can exist in three different redox states. , Salen- and salan-type ligands, example (c), can be redox active through the iminophenolate moiety. In the center row, (d) is S = 1 [Ni(NacNac) 2 ] whose singly oxidized form, [Ni(NacNac) 2 ] + , shows loss of a fractional 0.80 spin from the ligand and only 0.20 from the metal center .…”

Section: Introductionmentioning

confidence: 99%

Thiolate-Thione Redox-Active Ligand with a Six-Membered Chelate Ring via Template Condensation and Its Pt(II) Complexes

et al. 2021

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A new template condensation reaction has been discovered in a mixture of Pt(II), thiobenzamide, and base. Four complexes of the general form [Pt(ctaPhR)2], R = CH3 (1a), H (1b), F (1c), Cl (1d), cta = condensed thioamide, have been prepared under similar conditions and thoroughly characterized by 1H NMR and UV–vis-NIR spectroscopy, (spectro)electrochemistry, elemental analysis, and single-crystal X-ray diffraction. The ligand is redox active and can be reduced from the initial monoanion to a dianionic and then trianionic state. Chemical reduction of 1a with [Cp2Co] yielded [Cp2Co]2[Pt(ctaPhCH3)2], [Cp 2 Co] 2 [1a], which has been similarly characterized with the addition of EPR spectroscopy and SQUID magnetization. The singly reduced form containing [1a] 1– , (nBu4N)[Pt(ctaPhCH3)2], has been generated in situ and characterized by UV–vis and EPR spectroscopies. DFT studies of 1b, [1b] 1– , and [1b] 2– confirm the location of additional electrons in exclusively ligand-based orbitals. A detailed analysis of this redox-active ligand, with emphasis on the characteristics that favor noninnocent behavior in six-membered chelate rings, is included.

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Ligand field-actuated redox-activity of acetylacetonate

Abstract: The quest for simple ligands that enable multi-electron metal-ligand redox chemistry is driven by a desire to replace noble metals in catalysis and to discover novel chemical reactivity. The vast...

Cited by 13 publications

References 48 publications

Molecular Valence Tautomeric Metal Complexes for Chemosensing

Molecular Valence Tautomeric Metal Complexes for Chemosensing

Systematic Trends in the Electrochemical Properties of Transition Metal Hydride Complexes Discovered by Using the Ligand Acidity Constant Equation

Thiolate-Thione Redox-Active Ligand with a Six-Membered Chelate Ring via Template Condensation and Its Pt(II) Complexes

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