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Iridium(III) Hydrido N-Heterocyclic Carbene–Phosphine Complexes as Catalysts in Magnetization Transfer Reactions

[Image: see text] The hyperpolarization (HP) method signal amplification by reversible exchange (SABRE) uses para-hydrogen to sensitize substrate detection by NMR. The catalyst systems [Ir(H)(2)(IMes)(MeCN)(2)(R)]BF(4) and [Ir(H)(2)(IMes)(py)(2)(R)]BF(4) [py = pyridine; R = PCy(3) or PPh(3); IMes =...

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Autores principales: Fekete, Marianna, Bayfield, Oliver, Duckett, Simon B., Hart, Sam, Mewis, Ryan E., Pridmore, Natalie, Rayner, Peter J., Whitwood, Adrian
Formato: Online Artículo Texto
Lenguaje:English
Publicado: American Chemical Society 2013
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3850244/
https://www.ncbi.nlm.nih.gov/pubmed/24215616
http://dx.doi.org/10.1021/ic401783c
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author Fekete, Marianna
Bayfield, Oliver
Duckett, Simon B.
Hart, Sam
Mewis, Ryan E.
Pridmore, Natalie
Rayner, Peter J.
Whitwood, Adrian
author_facet Fekete, Marianna
Bayfield, Oliver
Duckett, Simon B.
Hart, Sam
Mewis, Ryan E.
Pridmore, Natalie
Rayner, Peter J.
Whitwood, Adrian
author_sort Fekete, Marianna
collection PubMed
description [Image: see text] The hyperpolarization (HP) method signal amplification by reversible exchange (SABRE) uses para-hydrogen to sensitize substrate detection by NMR. The catalyst systems [Ir(H)(2)(IMes)(MeCN)(2)(R)]BF(4) and [Ir(H)(2)(IMes)(py)(2)(R)]BF(4) [py = pyridine; R = PCy(3) or PPh(3); IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene], which contain both an electron-donating N-heterocyclic carbene and a phosphine, are used here to catalyze SABRE. They react with acetonitrile and pyridine to produce [Ir(H)(2)(NCMe)(py)(IMes)(PPh(3))]BF(4) and [Ir(H)(2)(NCMe)(py)(IMes)(PCy(3))]BF(4), complexes that undergo ligand exchange on a time scale commensurate with observation of the SABRE effect, which is illustrated here by the observation of both pyridine and acetonitrile HP. In this study, the required symmetry breaking that underpins SABRE is provided for by the use of chemical inequivalence rather than the previously reported magnetic inequivalence. As a consequence, we show that the ligand sphere of the polarization transfer catalyst itself becomes hyperpolarized and hence that the high-sensitivity detection of a number of reaction intermediates is possible. These species include [Ir(H)(2)(NCMe)(py)(IMes)(PPh(3))]BF(4), [Ir(H)(2)(MeOH)(py)(IMes)(PPh(3))]BF(4), and [Ir(H)(2)(NCMe)(py)(2)(PPh(3))]BF(4). Studies are also described that employ the deuterium-labeled substrates CD(3)CN and C(5)D(5)N, and the labeled ligands P(C(6)D(5))(3) and IMes-d(22), to demonstrate that dramatically improved levels of HP can be achieved as a consequence of reducing proton dilution and hence polarization wastage. By a combination of these studies with experiments in which the magnetic field experienced by the sample at the point of polarization transfer is varied, confirmation of the resonance assignments is achieved. Furthermore, when [Ir(H)(2)(pyridine-h(5))(pyridine-d(5))(IMes)(PPh(3))]BF(4) is examined, its hydride ligand signals are shown to become visible through para-hydrogen-induced polarization rather than SABRE.
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spelling pubmed-38502442013-12-05 Iridium(III) Hydrido N-Heterocyclic Carbene–Phosphine Complexes as Catalysts in Magnetization Transfer Reactions Fekete, Marianna Bayfield, Oliver Duckett, Simon B. Hart, Sam Mewis, Ryan E. Pridmore, Natalie Rayner, Peter J. Whitwood, Adrian Inorg Chem [Image: see text] The hyperpolarization (HP) method signal amplification by reversible exchange (SABRE) uses para-hydrogen to sensitize substrate detection by NMR. The catalyst systems [Ir(H)(2)(IMes)(MeCN)(2)(R)]BF(4) and [Ir(H)(2)(IMes)(py)(2)(R)]BF(4) [py = pyridine; R = PCy(3) or PPh(3); IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene], which contain both an electron-donating N-heterocyclic carbene and a phosphine, are used here to catalyze SABRE. They react with acetonitrile and pyridine to produce [Ir(H)(2)(NCMe)(py)(IMes)(PPh(3))]BF(4) and [Ir(H)(2)(NCMe)(py)(IMes)(PCy(3))]BF(4), complexes that undergo ligand exchange on a time scale commensurate with observation of the SABRE effect, which is illustrated here by the observation of both pyridine and acetonitrile HP. In this study, the required symmetry breaking that underpins SABRE is provided for by the use of chemical inequivalence rather than the previously reported magnetic inequivalence. As a consequence, we show that the ligand sphere of the polarization transfer catalyst itself becomes hyperpolarized and hence that the high-sensitivity detection of a number of reaction intermediates is possible. These species include [Ir(H)(2)(NCMe)(py)(IMes)(PPh(3))]BF(4), [Ir(H)(2)(MeOH)(py)(IMes)(PPh(3))]BF(4), and [Ir(H)(2)(NCMe)(py)(2)(PPh(3))]BF(4). Studies are also described that employ the deuterium-labeled substrates CD(3)CN and C(5)D(5)N, and the labeled ligands P(C(6)D(5))(3) and IMes-d(22), to demonstrate that dramatically improved levels of HP can be achieved as a consequence of reducing proton dilution and hence polarization wastage. By a combination of these studies with experiments in which the magnetic field experienced by the sample at the point of polarization transfer is varied, confirmation of the resonance assignments is achieved. Furthermore, when [Ir(H)(2)(pyridine-h(5))(pyridine-d(5))(IMes)(PPh(3))]BF(4) is examined, its hydride ligand signals are shown to become visible through para-hydrogen-induced polarization rather than SABRE. American Chemical Society 2013-11-11 2013-12-02 /pmc/articles/PMC3850244/ /pubmed/24215616 http://dx.doi.org/10.1021/ic401783c Text en Copyright © 2013 American Chemical Society Terms of Use CC-BY (http://pubs.acs.org/page/policy/authorchoice_ccby_termsofuse.html)
spellingShingle Fekete, Marianna
Bayfield, Oliver
Duckett, Simon B.
Hart, Sam
Mewis, Ryan E.
Pridmore, Natalie
Rayner, Peter J.
Whitwood, Adrian
Iridium(III) Hydrido N-Heterocyclic Carbene–Phosphine Complexes as Catalysts in Magnetization Transfer Reactions
title Iridium(III) Hydrido N-Heterocyclic Carbene–Phosphine Complexes as Catalysts in Magnetization Transfer Reactions
title_full Iridium(III) Hydrido N-Heterocyclic Carbene–Phosphine Complexes as Catalysts in Magnetization Transfer Reactions
title_fullStr Iridium(III) Hydrido N-Heterocyclic Carbene–Phosphine Complexes as Catalysts in Magnetization Transfer Reactions
title_full_unstemmed Iridium(III) Hydrido N-Heterocyclic Carbene–Phosphine Complexes as Catalysts in Magnetization Transfer Reactions
title_short Iridium(III) Hydrido N-Heterocyclic Carbene–Phosphine Complexes as Catalysts in Magnetization Transfer Reactions
title_sort iridium(iii) hydrido n-heterocyclic carbene–phosphine complexes as catalysts in magnetization transfer reactions
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3850244/
https://www.ncbi.nlm.nih.gov/pubmed/24215616
http://dx.doi.org/10.1021/ic401783c
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