Structure and Dynamics of 3,5-Di-tert-butylpyrazole Probed by Combined X-ray Crystallography and 15N Solid State NMR

Aguilar‐Parrilla, Francisco; Limbach, Hans−Heinrich; Foces‐Foces, Concepción; Cano, F. H.; Jagerovic, Nadine; Elguero, José

doi:10.1021/jo00112a015

Cited by 40 publications

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“…Multiple proton transfers in solid pyrazole dimers, trimers and tetramers ( Fig. 1e to 1g) are slower and have been studied by 15 N NMR magnetization transfer and line shape analysis [23][24][25][26][27][28][29][30][31]. The fastest process in Fig.…”

Section: Introductionmentioning

confidence: 99%

Kinetics of Coupled Double Proton and Deuteron Transfer in Hydrogen-Bonded Ribbons of Crystalline Pyrazole-4-carboxylic Acid

Torres

Lopez

Langer

et al. 2012

Zeitschrift Für Physikalische Chemie

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The proton tautomerism of pyrazole-4-carboxylic acid (PCA) has been studied by a combination of 15 N CPMAS and 2 H NMR spectroscopy and relaxometry. Down to 250 K, PCA forms a hydrogen bonded ribbon where adjacent carboxylic and pyrazole groups are linked by an OH· · ·N and an O· · ·HN hydrogen bond, forming either the tautomeric state A or B. Down to about 250 K, the tautomerism is fast on the NMR timescale and degenerate, corresponding to a phase exhibiting dynamic proton disorder. At lower temperatures, a transition to an ordered phase is observed with localized protons, assigned to an all-syn conformation adopting the sequence of tautomeric states ..ABABA.. The longitudinal 15 N relaxation times T 1 of PCA-15 N 2 have been measured at 9.12 MHz (2.1 T). Because of the low field, a chemical shift anisotropy mechanism could be neglected, and the data were analyzed in terms of a dipolar 1 H-15 N relaxation mechanism, yielding the rate constants k HH . The rate constants k HD and k DD were obtained from the measurement and analysis of the 2 H T 1 values of PCA-15 N 1 -d 0.9 and PCA-15 N 1 -d 0.1 measured at 46.03 MHz. Within the margin of error, no kinetic isotope effects could be detected, in contrast to previous results reported for the very fast tautomerism of solid benzoic acid dimers and the much slower tautomerism of solid 3,5-diphenyl-4-brompyrazole (DPBrP) dimers. The Arrhenius curves of all three systems were simulated using the Bell-Limbach tunneling model. Evidence for a major heavy atom motion for the tautomerism of PCA is obtained, associated with small angle reorientation of PCA molecules Brought to you by | University of California Authenticated Download Date | 8/25/15 5:13 PM 1126 V. Torres et al.around the molecular axis. The observed proton order-disorder transition and the mechanism of the observed rate process are discussed in terms of a coupling of adjacent tautomeric states.

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Section: Introductionmentioning

confidence: 99%

Kinetics of Coupled Double Proton and Deuteron Transfer in Hydrogen-Bonded Ribbons of Crystalline Pyrazole-4-carboxylic Acid

Torres

Lopez

Langer

et al. 2012

Zeitschrift Für Physikalische Chemie

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“…Pyrazoles and particularly 3,5-dimethylpyrazole (1), show a dynamic process in the solid state that consists in the transfer, generally concerted, of several protons between the nitrogen atoms [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. This process (named SSPT, Solid State Proton Transfer) is illustrated in Fig.…”

Section: Introductionmentioning

confidence: 99%

Pyrazoles as molecular probes to study the properties of co-crystals by solid state NMR spectroscopy

et al. 2004

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Equimolar mixtures of 3,5-dimethylpyrazole (1) with four NH-imidazoles (2-5) have been studied by 13 C and 15 N CPMAS NMR and by DSC. In three cases, the solid mixture behaves as the sum of the individual components [imidazole (2), 2-methylimidazole (3) and 2,4(5)-dimethylimidazole (5)]. In one case [4,5-dimethylimidazole (4)], the mixture corresponds to a new species in which the dynamic behavior of 1 no longer exists.

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“…Comparison to that of previously characterised t-Bu 2 pzH shows the bromine atom exerting little structural influence. [51,52] However, whereas the tert-butyl groups of t-Bu 2 pzH are rotationally disordered, the additional bromine atom in tBu 2 -4-BrpzH seems to prevent it as no disorder is observed. The molecular structure is shown in Figure 3 along with selected bond lengths and angles.…”

Section: Molecular Structure Of T-bu 2 -4-brpzhmentioning

confidence: 99%

Oxygen‐Transfer Reactions of Molybdenum‐ and Tungstendioxo Complexes Containing η²‐Pyrazolate Ligands

et al. 2005

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Dioxomolybdenum and -tungsten compounds containing sterically demanding pyrazolate ligands have been synthesised by treatment of dioxometal halides with the potassium salts of 3,5-ditert-butylpyrazole (t-Bu 2 pzH) and 3,5-di-tert-butyl-4-bromopyrazole (t-Bu 2 -4-BrpzH). The products (5) were characterised by spectroscopic techniques. The X-ray structure of complex 3 reveals a distorted trigonal prismatic geometry with two h 2 -co-ordinated pyrazolate ligands. These high-valent compounds participate in oxygentransfer reactions and catalyse the oxidation of PPh 3 with dimethyl sulphoxide. UV/VIS measurements of the oxo-transfer reactions and the kinetics of the catalytic process are described. By the reaction of 2 with three equivalents of PEt 3 or treatment of [MoOCl 2 -(PMe 3 ) 2 ] with two equivalents of t-Bu 2 pzK mononuclear mono-oxo compounds of the type [MoO(t-Bu 2 -pz) 2 (PR 3 ) 2 ] (R¼ Et 6, R¼ Me 7) were obtained and characterised by X-ray diffraction analyses. This points to biologically relevant mononuclear Mo(IV) intermediates in the catalytic process with this type of complex.

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Structure and Dynamics of 3,5-Di-tert-butylpyrazole Probed by Combined X-ray Crystallography and 15N Solid State NMR

Cited by 40 publications

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Kinetics of Coupled Double Proton and Deuteron Transfer in Hydrogen-Bonded Ribbons of Crystalline Pyrazole-4-carboxylic Acid

Kinetics of Coupled Double Proton and Deuteron Transfer in Hydrogen-Bonded Ribbons of Crystalline Pyrazole-4-carboxylic Acid

Pyrazoles as molecular probes to study the properties of co-crystals by solid state NMR spectroscopy

Oxygen‐Transfer Reactions of Molybdenum‐ and Tungstendioxo Complexes Containing η²‐Pyrazolate Ligands

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Structure and Dynamics of 3,5-Di-tert-butylpyrazole Probed by Combined X-ray Crystallography and 15N Solid State NMR

Cited by 40 publications

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Kinetics of Coupled Double Proton and Deuteron Transfer in Hydrogen-Bonded Ribbons of Crystalline Pyrazole-4-carboxylic Acid

Kinetics of Coupled Double Proton and Deuteron Transfer in Hydrogen-Bonded Ribbons of Crystalline Pyrazole-4-carboxylic Acid

Pyrazoles as molecular probes to study the properties of co-crystals by solid state NMR spectroscopy

Oxygen‐Transfer Reactions of Molybdenum‐ and Tungstendioxo Complexes Containing η2‐Pyrazolate Ligands

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Oxygen‐Transfer Reactions of Molybdenum‐ and Tungstendioxo Complexes Containing η²‐Pyrazolate Ligands