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The reaction of an iridium PNP complex with parahydrogen facilitates polarisation transfer without chemical change.

Holmes AJ, Rayner PJ, Cowley MJ, Green GG, Whitwood AC, Duckett SB - Dalton Trans (2015)

Bottom Line: The short lived pincer complex [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(py)]BF4 is shown to be active for signal amplification by reversible exchange.When the catalysts (1)H nuclei are replaced by (2)H, increased levels of substrate hyperpolarization result and when the reverse situation is examined the catalyst itself is clearly visible through hyperpolarised signals.The ligand exchange pathways of [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(py)]BF4 that are associated with this process are shown to involve the formation of 16-electron [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2]BF4 and the 18-electron H2 addition product [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(H2)]BF4.

View Article: PubMed Central - PubMed

Affiliation: Centre for Hyperpolarization in Magnetic Resonance, University of York, York Science Park, York, YO10 5NY, UK. simon.duckett@york.ac.uk.

ABSTRACT
The short lived pincer complex [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(py)]BF4 is shown to be active for signal amplification by reversible exchange. This catalyst formulation enables the efficient transfer of polarization from parahydrogen to be placed into just a single molecule of the hyperpolarisation target, pyridine. When the catalysts (1)H nuclei are replaced by (2)H, increased levels of substrate hyperpolarization result and when the reverse situation is examined the catalyst itself is clearly visible through hyperpolarised signals. The ligand exchange pathways of [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(py)]BF4 that are associated with this process are shown to involve the formation of 16-electron [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2]BF4 and the 18-electron H2 addition product [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(H2)]BF4.

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Series of hyperpolarized 1H NMR spectra showing how the appearance of the free pyridine signals change with change in the magnitude of the polarization transfer field experienced by 4.
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fig3: Series of hyperpolarized 1H NMR spectra showing how the appearance of the free pyridine signals change with change in the magnitude of the polarization transfer field experienced by 4.

Mentions: The signal intensity gain for the ortho-protons of free pyridine increases to 12.3-fold over their normal level when the magnetic field where polarization transfer takes place is increased to 65 G. This field change also results in all three of the free pyridine proton signals taking up the same phase with their relative intensities becoming 1 : 0.84 : 0.26 respectively. In these 1H NMR spectra, SABRE enhanced resonances are also seen at δ 9.30 (ortho), 8.06 (para) 7.24 (meta) which are due to the bound pyridine ligand of 4, and at δ 7.64 and 7.91 for the pincer's pyridine protons. These data confirm that polarization flows from p-H2 first into the proton nuclei of the two ligands of 4 that lie trans to the two hydride ligands. Dissociation of bound pyridine ligand then accounts for the detection of hyperpolarised free pyridine in solution. It is noteworthy that the 1H NMR signal that is seen for the residual acetonitrile present in these samples does not receive any visible polarisation which is consistent with the failure to observed PHIP in 2. Fig. 3 shows how the signal intensity changes for the free pyridine proton resonances as the polarization transfer field increases from 0.5 G to 145 G in steps of 25 G.


The reaction of an iridium PNP complex with parahydrogen facilitates polarisation transfer without chemical change.

Holmes AJ, Rayner PJ, Cowley MJ, Green GG, Whitwood AC, Duckett SB - Dalton Trans (2015)

Series of hyperpolarized 1H NMR spectra showing how the appearance of the free pyridine signals change with change in the magnitude of the polarization transfer field experienced by 4.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4295814&req=5

fig3: Series of hyperpolarized 1H NMR spectra showing how the appearance of the free pyridine signals change with change in the magnitude of the polarization transfer field experienced by 4.
Mentions: The signal intensity gain for the ortho-protons of free pyridine increases to 12.3-fold over their normal level when the magnetic field where polarization transfer takes place is increased to 65 G. This field change also results in all three of the free pyridine proton signals taking up the same phase with their relative intensities becoming 1 : 0.84 : 0.26 respectively. In these 1H NMR spectra, SABRE enhanced resonances are also seen at δ 9.30 (ortho), 8.06 (para) 7.24 (meta) which are due to the bound pyridine ligand of 4, and at δ 7.64 and 7.91 for the pincer's pyridine protons. These data confirm that polarization flows from p-H2 first into the proton nuclei of the two ligands of 4 that lie trans to the two hydride ligands. Dissociation of bound pyridine ligand then accounts for the detection of hyperpolarised free pyridine in solution. It is noteworthy that the 1H NMR signal that is seen for the residual acetonitrile present in these samples does not receive any visible polarisation which is consistent with the failure to observed PHIP in 2. Fig. 3 shows how the signal intensity changes for the free pyridine proton resonances as the polarization transfer field increases from 0.5 G to 145 G in steps of 25 G.

Bottom Line: The short lived pincer complex [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(py)]BF4 is shown to be active for signal amplification by reversible exchange.When the catalysts (1)H nuclei are replaced by (2)H, increased levels of substrate hyperpolarization result and when the reverse situation is examined the catalyst itself is clearly visible through hyperpolarised signals.The ligand exchange pathways of [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(py)]BF4 that are associated with this process are shown to involve the formation of 16-electron [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2]BF4 and the 18-electron H2 addition product [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(H2)]BF4.

View Article: PubMed Central - PubMed

Affiliation: Centre for Hyperpolarization in Magnetic Resonance, University of York, York Science Park, York, YO10 5NY, UK. simon.duckett@york.ac.uk.

ABSTRACT
The short lived pincer complex [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(py)]BF4 is shown to be active for signal amplification by reversible exchange. This catalyst formulation enables the efficient transfer of polarization from parahydrogen to be placed into just a single molecule of the hyperpolarisation target, pyridine. When the catalysts (1)H nuclei are replaced by (2)H, increased levels of substrate hyperpolarization result and when the reverse situation is examined the catalyst itself is clearly visible through hyperpolarised signals. The ligand exchange pathways of [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(py)]BF4 that are associated with this process are shown to involve the formation of 16-electron [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2]BF4 and the 18-electron H2 addition product [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(H2)]BF4.

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