Electron spin resonance studies of hyperconjugation in 2,3-, 2,6-, and 2,7-dimethylanthracene cation and anion radicals

Valenzuela, Jorge; Bard, Allen J.

doi:10.1021/j100724a004

Cited by 13 publications

(3 citation statements)

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“…However, EPR parameters computed for a model of 9 in which the Ag had been removed while keeping the geometry of the ligand identical (Figure S48) revealed qualitatively similar hyperfine constants ( A iso [ 31 P] = 52 MHz), suggesting a limited role for the metal in the observed coupling. We instead hypothesize that this hyperfine interaction is the result of hyperconjugation mediated by the phenylene linker …”

Section: Resultsmentioning

confidence: 94%

Copper and Silver Complexes of a Redox-Active Diphosphine-Diboraanthracene Ligand

et al. 2018

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Redox-active ligands and Z-type acceptor ligands have emerged as promising strategies for promoting multielectron redox chemistry at transition-metal centers. Herein, we report the synthesis and characterization of copper and silver complexes of a diphosphine ligand featuring a d i b o r a a n t h r a c e n e c o r e ( B 2 P 2 , 9,10-bis(2-(diisopropylphosphino)phenyl)-9,10-dihydroboranthrene) that is capable of serving as both a redox reservoir and a Ztype ligand. Metalation of B 2 P 2 with CuX (X = Cl, Br, I) results in the formation of bimetallic complexes of the formula (B 2 P 2 )Cu 2 X 2 of two different structure types, depending on the halide. The Cu(I) cation [Cu(B 2 P 2 )] + can be accessed by direct metalation of B 2 P 2 with [Cu(CH 3 CN) 4 ][PF 6 ] or by halide abstraction with Na[BAr F 4 ] (Ar F = 3,5-bis(trifluoromethyl)phenyl) with concomitant expulsion of CuX from the bimetallic Cu 2 X 2 complexes. Metalation of B 2 P 2 with AgCl results in the formation of the zwitterion Ag(B 2 P 2 )Cl featuring a diphosphine Ag cation tethered to a chloroborate anion. Metathesis of chloride for the noncoordinating [BAr F 4 ] − affords the cation [Ag(B 2 P 2 )] + . The cations [Cu(B 2 P 2 )]+ and [Ag(B 2 P 2 )] + exhibit quasireversible reduction events at ∼ −1.6 V versus the ferrocene/ferrocenium redox couple, and the thermally sensitive radicals that result from their reduction, Cu(B 2 P 2 ) and Ag(B 2 P 2 ), were characterized by EPR spectroscopy and, in the case of the latter, singlecrystal X-ray diffraction. Electronic structure calculations suggest these neutral radicals are best described as zwitterions with reduction centered at the diboraanthracene core.

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Section: Resultsmentioning

confidence: 94%

Copper and Silver Complexes of a Redox-Active Diphosphine-Diboraanthracene Ligand

et al. 2018

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“…R-I is a classic system in magnetic resonance studies [ 23 ], and its spectrum has 175 resonance lines. The unpaired spin in an R-I cation radical delocalizes onto the methyl groups [ 23 , 24 ] and hence the strongest hyperfine interactions caused by the six equivalent methyl protons split the central resonance line into seven lines. Four ortho-protons of the aromatic rings split each of those lines into five, followed by splitting of each lines into another five lines by the meta-protons.…”

Section: Methodsmentioning

confidence: 99%

Hyperfine Decoupling of ESR Spectra Using Wavelet Transform

Roy

Srivastava

2022

Magnetochemistry

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The objective of spectral analysis is to resolve and extract relevant features from experimental data in an optimal fashion. In continuous-wave (cw) electron spin resonance (ESR) spectroscopy, both g values of a paramagnetic center and hyperfine splitting (A) caused by its interaction with neighboring magnetic nuclei in a molecule provide important structural and electronic information. However, in the presence of g- and/or A-anisotropy and/or large number of resonance lines, spectral analysis becomes highly challenging. Either high-resolution experimental techniques are employed to resolve the spectra in those cases or a range of suitable ESR frequencies are used in combination with simulations to identify the corresponding g and A values. In this work, we present a wavelet transform technique in resolving both simulated and experimental cw-ESR spectra by separating the hyperfine and super-hyperfine components. We exploit the multiresolution property of wavelet transforms that allow the separation of distinct features of a spectrum based on simultaneous analysis of spectrum and its varying frequency. We retain the wavelet components that stored the hyperfine and/or super-hyperfine features, while eliminating the wavelet components representing the remaining spectrum. We tested the method on simulated cases of metal–ligand adducts at L-, S-, and X-band frequencies, and showed that extracted g values, hyperfine and super-hyperfine coupling constants from simulated spectra, were in excellent agreement with the values of those parameters used in the simulations. For the experimental case of a copper(II) complex with distorted octahedral geometry, the method was able to extract g and hyperfine coupling constant values, and revealed features that were buried in the overlapped spectra.

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“…In the case of 17 •ϩ , however, the ESR spectrum was not sufficiently resolved to allow a detailed analysis. The assignments of the splittings were made by means of their relative signs, the different substitution pattern, and in relation to reported ESR results of the anthracene radical cation [26] [27] and its 2,3- [28] and 9,10-dimethyl derivatives [27] [29] . Even with all this infor- 1 H-ENDOR spectrum of 3b…”

Section: Bmentioning

confidence: 99%

Intramolecular Electron Transfer between Terminal 1,4-Dimethoxybenzene Units in Radical Cations with a [2.2](1,4)Naphthalenophane, [2.2](1,4)Anthracenophane, and Pentacene Skeleton

Wartini¹,

Staab²,

Neugebauer³

1998

Eur. J. Org. Chem.

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Electron spin resonance studies of hyperconjugation in 2,3-, 2,6-, and 2,7-dimethylanthracene cation and anion radicals

Abstract: 1) To whom all correspondence and requests for reprints should be directed.

Cited by 13 publications

References 1 publication

Copper and Silver Complexes of a Redox-Active Diphosphine-Diboraanthracene Ligand

Copper and Silver Complexes of a Redox-Active Diphosphine-Diboraanthracene Ligand

Hyperfine Decoupling of ESR Spectra Using Wavelet Transform

Intramolecular Electron Transfer between Terminal 1,4-Dimethoxybenzene Units in Radical Cations with a [2.2](1,4)Naphthalenophane, [2.2](1,4)Anthracenophane, and Pentacene Skeleton

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