Parahydrogen-induced polarization with a metal-free P–P biradicaloid

Живонитко, Владимир В.; Bresien, Jonas; Schulz, Axel; Koptyug, Igor V.

doi:10.1039/c8cp07625a

Cited by 13 publications

(21 citation statements)

References 31 publications

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“…In both cases, the symmetry properties of the resulting AA'XX’, wherein A and A’ nuclei come from parahydrogen, allows inherent hyperpolarization of X nuclei. This feature was demonstrated for 31 P in 8 ‐H 2 adduct, [13] providing up to ca. 300‐fold signal enhancement.…”

Section: Methodsmentioning

confidence: 77%

“…The signal enhancements are observed for “forbidden” transitions, which are not considered in that theory. At the same time, it is possible to use SLIC (Spin‐Lock Induced Crossing) [16] to convert antiphase polarization to in‐phase, which was shown for 8 earlier [13] …”

Section: Methodsmentioning

confidence: 98%

“…These are mainly N−B intramolecular frustrated Lewis pairs (FLP) ( 1 – 7 ) such as ansa‐amino boranes, [11] and there is also an example of FLP based C−P pair of aromatic triphosphabenzene 7 [12] . Quite recently, a P−P biradicaloid 8 was demonstrated to show hyperpolarization effects both in 1 H and 31 P NMR spectra while activating parahydrogen molecules [13] . The symmetry of 8 ‐H 2 adduct led to observation of unusual 1 H and 31 P signal multiplets with enhancements exceeding at least one order of magnitude at 7 Tesla.…”

Section: Methodsmentioning

confidence: 99%

“…[12] Quite recently, a PÀ P biradicaloid 8 was demonstrated to show hyperpolarization effects both in 1 H and 31 P NMR spectra while activating parahydrogen molecules. [13] The symmetry of 8-H 2 adduct led to observation of unusual 1 H and 31 P signal multiplets with enhancements exceeding at least one order of magnitude at 7 Tesla.…”

mentioning

confidence: 99%

“…1 H signal enhancements for 8 are more than one order of magnitude, as was also shown elsewhere. [13] In principle, the signal enhancements in the symmetrical systems cannot be interpreted very easily in terms of conventional PASADENA theory in the weak coupling limit. [8a] The signal enhancements are observed for "forbidden" transitions, which are not considered in that theory.…”

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confidence: 99%

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Hyperpolarization Effects in Parahydrogen Activation with Pnictogen Biradicaloids: Metal‐free PHIP and SABRE

et al. 2021

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Biradicaloids attract attention as a novel class of reagents that can activate small molecules such as H2, ethylene and CO2. Herein, we study activation of parahydrogen (nuclear spin‐0 isomer of H2) by a number of 4‐ and 5‐membered pnictogen biradicaloids based on hetero‐cyclobutanediyl [X(μ‐NTer)2Z] and hetero‐cyclopentanediyl [X(μ‐NTer)2ZC(NDmp)] moieties (X,Z=P,As; Ter=2,6‐Mes2−C6H3, Dmp=2,6‐Me2−C6H3). The concerted mechanism of this reaction allowed observing strong nuclear spin hyperpolarization effects in 1H and 31P NMR experiments. Signal enhancements from two to four orders of magnitude were detected at 9.4 T depending on the structure. It is demonstrated that 4‐membered biradicaloids activate H2 reversibly, leading to SABRE (signal amplification by reversible exchange) hyperpolarization of biradicaloids themselves and their H2 adducts. In contrast, the 5‐membered counterparts demonstrate rather irreversible parahydrogen activation resulting in hyperpolarized H2 adducts only. Kinetic measurements provided parameters to support experimental observations.

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Section: Methodsmentioning

confidence: 77%

Section: Methodsmentioning

confidence: 98%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Hyperpolarization Effects in Parahydrogen Activation with Pnictogen Biradicaloids: Metal‐free PHIP and SABRE

et al. 2021

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A Zwitterionic Phosphonium Stannate(II) via Hydrogen Splitting by a Sn/P Frustrated Lewis‐Pair and Reductive Elimination

Holtkamp

Schwabedissen

Neumann

et al. 2020

Chemistry A European J

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The reactivity of the frustrated Lewis pair (FLP) (F 5 C 2) 3 SnCH 2 P(tBu) 2 (1)w as investigated with respectt o the activation of elemental hydrogen. The reaction of 1 at elevatedh ydrogen pressure afforded the intramolecular phosphonium stannate(II) (F 5 C 2) 2 SnCH 2 PH(tBu) 2 (3). It was characterizedb ym eans of multinuclearN MR spectroscopy and single crystal X-ray diffraction. NMRe xperiments with the two isotopologues H 2 and D 2 showed it to be formed via an H 2 adduct (F 5 C 2) 3 HSnCH 2 PH(tBu) 2 (2) andt he subsequent formal reductivee limination of pentafluoroethane; this is supported by DFT calculations. Parahydrogen-induced polarization experiments revealed the formation of as econd producto ft he reactiono f1 with H 2 , [HP(tBu) 2 Me][Sn(C 2 F 5) 3 ](4), in 1 HNMR spectra,w hereas 2 was not detected duetoi ts transient nature.

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Parahydrogen‐Induced Polarization in Hydrogenation Reactions Mediated by a Metal‐Free Catalyst

Zakharov

Chernichenko

Sorochkina

et al. 2022

Chemistry A European J

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We report nuclear spin hyperpolarization of various alkenes achieved in alkyne hydrogenations with parahydrogen over a metal-free hydroborane catalyst (HCAT). Being an intramolecular frustrated Lewis pair aminoborane, HCAT utilizes a non-pairwise mechanism of H 2 transfer to alkynes that normally prevents parahydrogen-induced polarization (PHIP) from being observed. Nevertheless, the specific spin dynamics in catalytic intermediates leads to the hyperpolarization of predominantly one hydrogen in alkene. PHIP enabled the detection of important HCAT-alkyne-H 2 intermediates through substantial 1 H, 11 B and 15 N signal enhancement and allowed advanced characterization of the catalytic process.Nuclear magnetic resonance provides versatile tools for structure elucidation and understanding dynamics at the molecular level. [1] It is also at the heart of magnetic resonance imaging (MRI), a non-invasive and highly informative imaging method. However, the low intrinsic sensitivity of NMR dictated by low thermal spin polarization often leads to the insufficient signal strengths to perform reliable analysis. To date, several spin hyperpolarization techniques have been developed to boost the sensitivity. [2] Among them, parahydrogen-induced polarization (PHIP) is based on the chemical activation of parahydrogen, [3] the nuclear spin-0 isomer of H 2 . The hyperpolarization is produced upon chemical addition of parahydrogen to a substrate due to breaking the magnetic equivalence of protons originating from parahydrogen. [4] The pair of H atoms must not be separated completely to observe the hyperpolarization, that is, the atoms must end up in the same molecule. These prerequisites are fulfilled, for instance, if parahydrogen molecules are involved in the homogeneous catalytic hydrogenations mediated by metal complexes. [3b,5] However, toxicity issues require efficient methods of catalyst separation from hyperpolarized products [6] and can limit their applications, especially in in vivo studies. Heterogeneous catalysts based on immobilized metal complexes, metal nanoparticles and binary metal compounds have also been demonstrated to enable PHIP. [7] The separation is easier in this case as compared to homogeneous catalysts but achieved hyperpolarization levels are typically quite modest.Metal-free homogeneous catalytic systems may provide essentially new alternatives for PHIP. Naturally, substances made of main biogenic elements can be more environmentally and biologically friendly as compared to their metal-containing counterparts. The mechanisms of H 2 activation, however, are significantly different for the metal and nonmetal extremes. Pioneered by Stephan et al., [8] activation of H 2 by frustrated Lewis pairs (FLPs) attracts extraordinary attention. First observations of spin hyperpolarization effects with metal-free systems were reported for ansa-aminoboranes (AABs), the intramolecular N-B FLPs of 2-boryl-benzylamine core. [9] Later, aromatic triphosphabenzene [10] and several novel 2-aminophenylboranes [11] were dem...

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Parahydrogen-induced polarization with a metal-free P–P biradicaloid

Abstract: The activation of parahydrogen by a metal-free P–P biradicaloid leads to 1H and 31P nuclear spin hyperpolarization.

Cited by 13 publications

References 31 publications

Hyperpolarization Effects in Parahydrogen Activation with Pnictogen Biradicaloids: Metal‐free PHIP and SABRE

Hyperpolarization Effects in Parahydrogen Activation with Pnictogen Biradicaloids: Metal‐free PHIP and SABRE

A Zwitterionic Phosphonium Stannate(II) via Hydrogen Splitting by a Sn/P Frustrated Lewis‐Pair and Reductive Elimination

Parahydrogen‐Induced Polarization in Hydrogenation Reactions Mediated by a Metal‐Free Catalyst

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