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

doi:10.1021/ic8020029

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 journal › Article › peer-review

97 Citations (Scopus)

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 language	English
Pages (from-to)	663-670
Number of pages	8
Journal	Inorganic Chemistry
Volume	48
Issue number	2
DOIs	https://doi.org/10.1021/ic8020029
Publication status	Published - 19 Jan 2009
Externally published	Yes

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@article{db2ada0cb277442fa01b2f95e599b16b,

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.",

author = "Atkinson, {Kevin D.} and Cowley, {Michael J.} and Duckett, {Simon B.} and Elliott, {Paul I P} and Green, {Gary G R} and Joaquin L{\'o}pez-Serrano and Khazal, {Iman G.} and Whitwood, {Adrian C.}",

year = "2009",

month = jan,

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doi = "10.1021/ic8020029",

language = "English",

volume = "48",

pages = "663--670",

journal = "Inorganic Chemistry",

issn = "0020-1669",

publisher = "American Chemical Society",

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TY - JOUR

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.

UR - http://www.scopus.com/inward/record.url?scp=60849113433&partnerID=8YFLogxK

U2 - 10.1021/ic8020029

DO - 10.1021/ic8020029

M3 - Article

C2 - 19072592

AN - SCOPUS:60849113433

VL - 48

SP - 663

EP - 670

JO - Inorganic Chemistry

JF - Inorganic Chemistry

SN - 0020-1669

IS - 2

ER -

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

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