Para-hydrogen induced polarization without incorporation of para-hydrogen into the analyte

Kevin D. Atkinson, Michael J. Cowley, Simon B. Duckett, Paul I P Elliott, Gary G R Green, Joaquin López-Serrano, Iman G. Khazal, Adrian C. Whitwood

Research output: Contribution to journalArticle

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Abstract

The cationic iridium complexes [lr(COD)(PR3)2]BF 4 (1a-c) (a, R = Ph; b, R = p-tolyl; c, R = p-C6H 4-OMe) react with parahydrogen in the presence of pyridine to give trans, cis, cis-[lr(PR3)2(py)2(H) 2]+ (2a-c) and small amounts of fac, cis-[lr(PR 3)(py)3(H)2]+ (3a-c), each of which exhibit polarized hydride resonances due to the magnetic inequivalence associated with the resultant AA"XX" spin system when 15N-labeled pyridine is employed. The pyridine ligands in 2 are labile, exchanging slowly into free pyridine with a rate constant of 0.4 s -1 for 2a at 335 K in a dissociative process where ΔH‡ = 134 ± 1 kJ mol-1 and AS‡= 151 ± 5 J mon -1 K-1. Pyridine ligand exchange in 2 proves to be slower than that determined for 3. Parahydrogen induced polarization (PHIP) based on the hydride ligands of 2 and 3 is transferred efficiently to the 15N nuclei of the bound pyridine ligand by suitable insensitive-nuclei-enhanced-by- polarization-transfer (INEPT) based procedures. Related methods are then used to facilitate the sensitization of the free pyridine 15N signal by a factor of 120-fold through ligand exchange even though this substrate does not contain parahydrogen. This therefore corresponds to the successful polarization of an analyte by parahydrogen induced polarization methods without the need for the actual chemical incorporation of any parahydrogen derived nuclei into it.

Original languageEnglish
Pages (from-to)663-670
Number of pages8
JournalInorganic Chemistry
Volume48
Issue number2
DOIs
Publication statusPublished - 19 Jan 2009
Externally publishedYes

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para hydrogen
Hydrogen
pyridines
Polarization
polarization
Ligands
ligands
Hydrides
hydrides
nuclei
Iridium
exchanging
crack opening displacement
pyridine
iridium
Rate constants
Substrates

Cite this

Atkinson, K. D., Cowley, M. J., Duckett, S. B., Elliott, P. I. P., Green, G. G. R., López-Serrano, J., ... Whitwood, A. C. (2009). Para-hydrogen induced polarization without incorporation of para-hydrogen into the analyte. Inorganic Chemistry, 48(2), 663-670. https://doi.org/10.1021/ic8020029
Atkinson, Kevin D. ; Cowley, Michael J. ; Duckett, Simon B. ; Elliott, Paul I P ; Green, Gary G R ; López-Serrano, Joaquin ; Khazal, Iman G. ; Whitwood, Adrian C. / Para-hydrogen induced polarization without incorporation of para-hydrogen into the analyte. In: Inorganic Chemistry. 2009 ; Vol. 48, No. 2. pp. 663-670.
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title = "Para-hydrogen induced polarization without incorporation of para-hydrogen into the analyte",
abstract = "The cationic iridium complexes [lr(COD)(PR3)2]BF 4 (1a-c) (a, R = Ph; b, R = p-tolyl; c, R = p-C6H 4-OMe) react with parahydrogen in the presence of pyridine to give trans, cis, cis-[lr(PR3)2(py)2(H) 2]+ (2a-c) and small amounts of fac, cis-[lr(PR 3)(py)3(H)2]+ (3a-c), each of which exhibit polarized hydride resonances due to the magnetic inequivalence associated with the resultant AA{"}XX{"} spin system when 15N-labeled pyridine is employed. The pyridine ligands in 2 are labile, exchanging slowly into free pyridine with a rate constant of 0.4 s -1 for 2a at 335 K in a dissociative process where ΔH‡ = 134 ± 1 kJ mol-1 and AS‡= 151 ± 5 J mon -1 K-1. Pyridine ligand exchange in 2 proves to be slower than that determined for 3. Parahydrogen induced polarization (PHIP) based on the hydride ligands of 2 and 3 is transferred efficiently to the 15N nuclei of the bound pyridine ligand by suitable insensitive-nuclei-enhanced-by- polarization-transfer (INEPT) based procedures. Related methods are then used to facilitate the sensitization of the free pyridine 15N signal by a factor of 120-fold through ligand exchange even though this substrate does not contain parahydrogen. This therefore corresponds to the successful polarization of an analyte by parahydrogen induced polarization methods without the need for the actual chemical incorporation of any parahydrogen derived nuclei into it.",
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Atkinson, KD, Cowley, MJ, Duckett, SB, Elliott, PIP, Green, GGR, López-Serrano, J, Khazal, IG & Whitwood, AC 2009, 'Para-hydrogen induced polarization without incorporation of para-hydrogen into the analyte', Inorganic Chemistry, vol. 48, no. 2, pp. 663-670. https://doi.org/10.1021/ic8020029

Para-hydrogen induced polarization without incorporation of para-hydrogen into the analyte. / Atkinson, Kevin D.; Cowley, Michael J.; Duckett, Simon B.; Elliott, Paul I P; Green, Gary G R; López-Serrano, Joaquin; Khazal, Iman G.; Whitwood, Adrian C.

In: Inorganic Chemistry, Vol. 48, No. 2, 19.01.2009, p. 663-670.

Research output: Contribution to journalArticle

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T1 - Para-hydrogen induced polarization without incorporation of para-hydrogen into the analyte

AU - Atkinson, Kevin D.

AU - Cowley, Michael J.

AU - Duckett, Simon B.

AU - Elliott, Paul I P

AU - Green, Gary G R

AU - López-Serrano, Joaquin

AU - Khazal, Iman G.

AU - Whitwood, Adrian C.

PY - 2009/1/19

Y1 - 2009/1/19

N2 - The cationic iridium complexes [lr(COD)(PR3)2]BF 4 (1a-c) (a, R = Ph; b, R = p-tolyl; c, R = p-C6H 4-OMe) react with parahydrogen in the presence of pyridine to give trans, cis, cis-[lr(PR3)2(py)2(H) 2]+ (2a-c) and small amounts of fac, cis-[lr(PR 3)(py)3(H)2]+ (3a-c), each of which exhibit polarized hydride resonances due to the magnetic inequivalence associated with the resultant AA"XX" spin system when 15N-labeled pyridine is employed. The pyridine ligands in 2 are labile, exchanging slowly into free pyridine with a rate constant of 0.4 s -1 for 2a at 335 K in a dissociative process where ΔH‡ = 134 ± 1 kJ mol-1 and AS‡= 151 ± 5 J mon -1 K-1. Pyridine ligand exchange in 2 proves to be slower than that determined for 3. Parahydrogen induced polarization (PHIP) based on the hydride ligands of 2 and 3 is transferred efficiently to the 15N nuclei of the bound pyridine ligand by suitable insensitive-nuclei-enhanced-by- polarization-transfer (INEPT) based procedures. Related methods are then used to facilitate the sensitization of the free pyridine 15N signal by a factor of 120-fold through ligand exchange even though this substrate does not contain parahydrogen. This therefore corresponds to the successful polarization of an analyte by parahydrogen induced polarization methods without the need for the actual chemical incorporation of any parahydrogen derived nuclei into it.

AB - The cationic iridium complexes [lr(COD)(PR3)2]BF 4 (1a-c) (a, R = Ph; b, R = p-tolyl; c, R = p-C6H 4-OMe) react with parahydrogen in the presence of pyridine to give trans, cis, cis-[lr(PR3)2(py)2(H) 2]+ (2a-c) and small amounts of fac, cis-[lr(PR 3)(py)3(H)2]+ (3a-c), each of which exhibit polarized hydride resonances due to the magnetic inequivalence associated with the resultant AA"XX" spin system when 15N-labeled pyridine is employed. The pyridine ligands in 2 are labile, exchanging slowly into free pyridine with a rate constant of 0.4 s -1 for 2a at 335 K in a dissociative process where ΔH‡ = 134 ± 1 kJ mol-1 and AS‡= 151 ± 5 J mon -1 K-1. Pyridine ligand exchange in 2 proves to be slower than that determined for 3. Parahydrogen induced polarization (PHIP) based on the hydride ligands of 2 and 3 is transferred efficiently to the 15N nuclei of the bound pyridine ligand by suitable insensitive-nuclei-enhanced-by- polarization-transfer (INEPT) based procedures. Related methods are then used to facilitate the sensitization of the free pyridine 15N signal by a factor of 120-fold through ligand exchange even though this substrate does not contain parahydrogen. This therefore corresponds to the successful polarization of an analyte by parahydrogen induced polarization methods without the need for the actual chemical incorporation of any parahydrogen derived nuclei into it.

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