Nuclear singlet/triplet mixing during hydrogenations with parahydrogen: an in situ NMR method to investigate catalytic reaction mechanisms and their kinetics. 2. Homogeneous hydrogenation of 1,4-dihydro-1,4-epoxynaphthalene using different rhodium catalysts

Kating, P.; Wandelt, A.; Selke, Rüdiger; Bargon, Joachim

doi:10.1021/j100152a040

Cited by 57 publications

(37 citation statements)

References 2 publications

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“…In the hydrogenation of 2,5-dihydrofuran, polarised resonances were observed for both the ␣ and ␤ protons of the product THF molecule; this was rationalised as a consequence of scalar coupling between the protons, although polarisation transfer via nOe was also cited as a possible explanation. The group conducted similar work into the rhodium-catalysed hydrogenation of 1,4-dihydro-1,4-epoxynaphthalene to 1,4-epoxytetralin, using RhCl(PPh 3 ) 3 and [Rh(COD)(Ph-␤-glup-OH)] + as catalysts [63]. The different catalysts produced different polarisation patterns in the 1 H NMR spectra of the hydrogenation products.…”

Section: Studies Of Catalytic Hydrogenation With Parahydrogenmentioning

confidence: 99%

Parahydrogen-based NMR methods as a mechanistic probe in inorganic chemistry

Duckett

Wood

2008

Coordination Chemistry Reviews

125

127

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Section: Studies Of Catalytic Hydrogenation With Parahydrogenmentioning

confidence: 99%

Parahydrogen-based NMR methods as a mechanistic probe in inorganic chemistry

Duckett

Wood

2008

Coordination Chemistry Reviews

125

127

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“…Scheme 1. Magnetic field induced conversion of p-H 2 (spin state S ) to o-H 2 in spin state 0 T according to Bargon et al [15][16] After oxidative addition to a transition metal complex L n M, where the two hydrogen nuclei exhibit different Larmor frequencies, the singlet state S with opposite phases of the nuclear spins is converted to the triplet sub-state 0 T , where the two spins are in-phase.…”

Section: Introductionmentioning

confidence: 99%

Parahydrogen Allows Ultrasensitive Indirect NMR Detection of Catalytic Hydrogen Complexes

et al. 2017

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The 1 H NMR signal of dissolved molecular hydrogen enriched in parahydrogen (p-H 2 ) exhibits in the presence of an organometallic hydrogenation catalyst an unusual, partially negative line shape (PNL). It results from a strongly enhanced two-spin order connected to the population of the 0 T level of orthohydrogen (o-H 2 ). This two-spin order is made visible by a slow asymmetric exchange process between free hydrogen and a transient catalyst-hydrogen complex. By Only Parahydrogen Spectroscopy (OPSY) it is possible to selectively detect the two-spin order and suppress the signal from the thermal o-H 2 . The intensity of the PNL can be strongly affected by the PArtially NEgative Line (PANEL) experiment, which irradiates a long narrow-band radio frequency (RF) pulse. When the RF-frequency is in resonance with the chemical shift values of the hydrogen bound to the elusive catalyst or of the free hydrogen, a strong intensity reduction of the PNL is observed. Numerical simulations of the experiments performed at 500 MHz and 700 MHz proton frequency show that the indirect detection has at least three orders of magnitude higher sensitivity than the normal NMR experiment. A theoretical model, including reversible binding and 0 S T − evolution, is developed, which reproduces the NMR line-shape, the nutation angle dependence and the dependence on the frequency of the irradiation field of the PNL and permits the determination of the proton chemical shift values and the sign of the scalar coupling in the transient NMR invisible complex where singlet-triplet conversion take place.

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“…9 It was also found that singlet-triplet mixing can occur on reaction intermediates and this can be exploited to gain mechanistic information about intermediate hydrogen complexes and an estimate of the dwell time of the hydrogen nuclei in magnetically inequivalent positions. 8 Transient dyhidride intermediates are extremely elusive and they have never been observed, except in one case, using parahydrogen with an unusually reactive complex at low temperature. 10 Nevertheless, hyperpolarization attained on products is often much lower than that theoretically predicted, 5 even with this kind of catalyst.…”

Section: Introductionmentioning

confidence: 99%

Role of the reaction intermediates in determining PHIP (parahydrogen induced polarization) effect in the hydrogenation of acetylene dicarboxylic acid with the complex [Rh (dppb)]+ (dppb: 1,4-bis(diphenylphosphino)butane)

Reineri

Aime

Gobetto

et al. 2014

The Journal of Chemical Physics

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Articles you may be interested inThis study deals with the parahydrogenation of the symmetric substrate acetylene dicarboxylic acid catalyzed by a Rh(I) complex bearing the chelating diphosphine dppb (1,4-bis(diphenylphosphino)butane). The two magnetically equivalent protons of the product yield a hyperpolarized emission signal in the 1 H-NMR spectrum. Their polarization intensity varies upon changing the reaction solvent from methanol to acetone. A detailed analysis of the hydrogenation pathway is carried out by means of density functional theory calculations to assess the structure of hydrogenation intermediates and their stability in the two solvents. The observed polarization effects have been accounted on the basis of the obtained structures. Insights into the lifetime of a short-lived reaction intermediate are also obtained. © 2014 AIP Publishing LLC.

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Nuclear singlet/triplet mixing during hydrogenations with parahydrogen: an in situ NMR method to investigate catalytic reaction mechanisms and their kinetics. 2. Homogeneous hydrogenation of 1,4-dihydro-1,4-epoxynaphthalene using different rhodium catalysts

Cited by 57 publications

References 2 publications

Parahydrogen-based NMR methods as a mechanistic probe in inorganic chemistry

Parahydrogen-based NMR methods as a mechanistic probe in inorganic chemistry

Parahydrogen Allows Ultrasensitive Indirect NMR Detection of Catalytic Hydrogen Complexes

Role of the reaction intermediates in determining PHIP (parahydrogen induced polarization) effect in the hydrogenation of acetylene dicarboxylic acid with the complex [Rh (dppb)]+ (dppb: 1,4-bis(diphenylphosphino)butane)

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