Structural, thermodynamic and kinetic consequences of a spectroscopic study of the equilibrium between isomeric forms of ferrocene-containing β-diketones

Plessis, W.C. du; Davis, Wade L.; Cronje, Sarina J.; Swarts, Jannie C.

doi:10.1016/s0020-1693(01)00292-4

Cited by 43 publications

(25 citation statements)

References 10 publications

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“…In particular, their keto-enol tautomerism has been extensively studied in solution by FT-IR and NMR spectroscopy and by electrochemistry and in the solid-state by X-ray single crystal diffraction analysis [11]. In solution, the 1,3-diketone cores generally exist as equilibrium mixtures of diketo [RC(O)CHR"C(O)R""] and enolone [RC(O)CR"=C(OH)R""] tautomers [10][11][12][13][14][15][16][17][18], whereas in the solid-state, the keto-enol isomer is generally the sole form observed [14][15][16][17][18][19]. This feature has been rationalized in terms of resonance-assisted hydrogen bond (RAHB) model based on intercorrelation between spectroscopic and crystal structure parameters, originally introduced by , for explaining the abnormally strong internal hydrogen bonding within the enolone fragment.…”

Section: Introductionmentioning

confidence: 99%

Anisyl and ferrocenyl adducts of methylenepyran-containing β-diketone: Synthesis, spectral, structural, and redox properties

Novoa¹,

Roisnel²,

Dorcet³

et al. 2014

Journal of Organometallic Chemistry

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International audienceWittig reaction between the in situ generated [2,6-diphenyl-4H-pyran-4-yl phosphorane and methyl 4-formylbenzoate afforded the methyl 4-[(2,6-diphenyl-4H-pyran-4-ylidene)methyl]benzoate precursor 2 in 75% yield. The anisyl and ferrocenyl adducts of methylenepyran-containing β-diketones 3 and 4, respectively, were prepared from the base-catalyzed Claisen condensation reaction between precursor 2 and 4-methoxyacetophenone or acetylferrocene, using t-BuO−K+ as basic initiator. Both β-diketones 3 and 4 were isolated as an orange and dark-red crystalline solids in 50% yield, respectively. The acetyl derivative 6, 1-acetyl-1′-methylenepyranyl-ferrocene, was synthesized following a classical Friedel-Crafts acylation reaction of the parent ferrocenylmethylenepyran 5, and isolated in 61% yield as a red microcrystalline powder. The condensation reaction between the electron-rich acetyl complex 6 and acetyl acetate, using lithium diisopropylamide as the active base initiator, provided the ferrocenylmethylenepyran-containing β-diketone, 1-(1,3-dioxobutyl)-1′-[(2,6-diphenyl-4H-pyran-4-ylidene)methyl] ferrocene 7, isolated in 20% yield as an orange powder. The composition and identity of the new compounds 2-4, 6 and 7 are supported by elemental analysis, FT-IR, one- and two-dimensional 1H and 13C NMR spectral data and mass spectrometry. Additionally, the molecular structures of compounds 2, 4 and 6 were ascertained by single-crystal X-ray diffraction study. FT-IR and NMR spectral data indicate that both β-diketones 3 and 4 do solely exist as their keto-enol tautomeric form in solution and in the solid state, whereas a mixture of keto-enol and β-diketone tautomers in a 73:27 spectroscopic ratio was observed for 7. In the three cases, enolization takes place exclusively away from the anisyl or ferrocenyl group with formation of a six-membered pseudo-aromatic keto-enol ring, confirmed by the crystal structure of 4. Cyclic voltammetric measurements revealed that all the compounds undergo a single one-electron oxidation, localized presumably at the methylenepyran unit. This first oxidation generates a radical cation that undergoes an intermolecular C-C bond coupling to form the corresponding dimer. Anodically shifted to the first oxidation, cyclovoltammogram of 4 exhibits one reversible two-electron oxidation while that of 6 and 7 present two successive reversible one-electron oxidations, attributed in the three cases to the ferrocenyl fragment of the dimer

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Section: Introductionmentioning

confidence: 99%

Anisyl and ferrocenyl adducts of methylenepyran-containing β-diketone: Synthesis, spectral, structural, and redox properties

Novoa¹,

Roisnel²,

Dorcet³

et al. 2014

Journal of Organometallic Chemistry

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“…On the other hand, the resonance driving force was suggested to determine the observed enol form by using bond distances arising from crystallographic determinations. [9][10][11] Due to difficulties in X-ray analysis and the lack of a general theoretical method, a theoretical method to predict was sought to predict which enol form could be the most abundant. It is well known that the dihedral angle affects conjugation, resonance and aromaticity.…”

Section: Dihedral Angle Studies Using the Dftmentioning

confidence: 99%

“…[9][10][11] Swarts and his group identified the observed enol form of some 1,3-dicarbonyl derivatives and discussed the reasons using cyclic voltammetry data, and electronic and resonance driving forces. [9][10][11] To the best of our knowledge, the research group has not studied the characterization of different enol forms using 2D NMR spectra and explained the cause with dihedral angles. In the present study, the dominant tautomers of the synthesized 1,3-dicarbonyl compounds and reasons of observed enol forms were discussed in terms of 1D, 2D NMR data and DFT calculations.…”

Section: Introductionmentioning

confidence: 99%

Determination of the enol form of asymmetric 1,3-dicarbonyl compounds: 2D HMBC NMR data and DFT calculations

2018

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In this study, a series of asymmetric aryl 1,3-dicarbonyl compounds were synthesized and their enol forms were observed via experimental data and theoretical calculations. According to the 1 Hand 13 C-NMR results, all the investigated compounds were found as a single enol form in CDCl 3 solution. Moreover, their HMBC spectra were applied to identify the observed enol forms and correlations between certain protons and carbon atoms were considered. The dihedral angles of the asymmetric compounds that have aryl units on both sides were calculated by DFT to understand the reason for the observed enol forms. Small dihedral angles caused longer conjugation, resulting in more stable compounds and it was found that the observed enol forms were based on small dihedral angles, namely, resonance is the driving force. Furthermore, the compounds possessing both aryl and alkyl moieties prefer the enol form towards the aromatic ring side due to longer conjugation.

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“…The 1,3--diketones 1-ferrocenylbutane-1,3-dione (HL 1 ; Fc-COCH 2 COCH 3 ; Cain et al 1961;Hennig & Gurtler, 1968;Bell et al, 1992;Zakaria et al;1995) and 1,3-diferrocenylpropane-1,3-dione (HL 2 ; FcCOCH 2 COFc; Woisetschlager et al, 1999;du Plessis et al, 1998du Plessis et al, , 2001) form coordination (Zanello et al, 1998;Che et al, 1998;Li et al, 2002) and organometallic complexes of interest in catalysis (Abiko & Wang, 1996Cullen et al, 1991;Swarts et al, 1993;Woisetschlager et al, 2000;Vosloo et al, 2002;Conradie et al, 2005).…”

Section: Commentmentioning

confidence: 99%

Bis(1-ferrocenylbutane-1,3-dionato-κ²O,O′)copper(II) and bis(1,3-diferrocenylpropane-1,3-dionato-κ²O,O′)copper(II)

2006

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The title compounds, [CuFe2(C5H5)2(C9H8O2)2], (I), and [CuFe4(C5H5)4(C13H9O2)2], (II), are four-coordinate square-planar copper(II) complexes with two bidentate 1-ferrocenylbutane-1,3-dionate or 1,3-diferrocenylpropane-1,3-dionate ligands, respectively. The copper ion in (I) lies on an inversion centre, with one-half of the molecule in the asymmetric unit, while in (II), there are two independent half molecules in the asymmetric unit, with the copper ions also situated on inversion centres. The ferrocene substituents in (I) are in an anti arrangement. The molecules assemble in the crystal structure in layers with ferrocene groups at the surface. The pairs of ferrocene substituents on each ligand in complex (II) are syn and these adopt an anti arrangement with respect to the pair on the other diketonate ligand. As found in (I), complexes assemble in a layered structure with ferrocene-coated surfaces.

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Structural, thermodynamic and kinetic consequences of a spectroscopic study of the equilibrium between isomeric forms of ferrocene-containing β-diketones

Cited by 43 publications

References 10 publications

Anisyl and ferrocenyl adducts of methylenepyran-containing β-diketone: Synthesis, spectral, structural, and redox properties

Anisyl and ferrocenyl adducts of methylenepyran-containing β-diketone: Synthesis, spectral, structural, and redox properties

Determination of the enol form of asymmetric 1,3-dicarbonyl compounds: 2D HMBC NMR data and DFT calculations

Bis(1-ferrocenylbutane-1,3-dionato-κ²O,O′)copper(II) and bis(1,3-diferrocenylpropane-1,3-dionato-κ²O,O′)copper(II)

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Structural, thermodynamic and kinetic consequences of a spectroscopic study of the equilibrium between isomeric forms of ferrocene-containing β-diketones

Cited by 43 publications

References 10 publications

Anisyl and ferrocenyl adducts of methylenepyran-containing β-diketone: Synthesis, spectral, structural, and redox properties

Anisyl and ferrocenyl adducts of methylenepyran-containing β-diketone: Synthesis, spectral, structural, and redox properties

Determination of the enol form of asymmetric 1,3-dicarbonyl compounds: 2D HMBC NMR data and DFT calculations

Bis(1-ferrocenylbutane-1,3-dionato-κ2O,O′)copper(II) and bis(1,3-diferrocenylpropane-1,3-dionato-κ2O,O′)copper(II)

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Bis(1-ferrocenylbutane-1,3-dionato-κ²O,O′)copper(II) and bis(1,3-diferrocenylpropane-1,3-dionato-κ²O,O′)copper(II)