Para-Hydrogen Induced Polarization without Incorporation of Para-Hydrogen into the Analyte
| Autor: | Kevin D. Atkinson, Gary G. R. Green, Iman G. Khazal, Joaquín López-Serrano, Adrian C. Whitwood, Michael J. Cowley, Paul I. P. Elliott, Simon B. Duckett |
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| Rok vydání: | 2008 |
| Předmět: |
Magnetic Resonance Spectroscopy
Nitrogen Phosphines Pyridines Stereochemistry chemistry.chemical_element Crystallography X-Ray Iridium Ligands Spin isomers of hydrogen Medicinal chemistry Induced polarization Inorganic Chemistry Cyclooctanes Magnetics chemistry.chemical_compound Reaction rate constant Pyridine Organometallic Compounds Physical and Theoretical Chemistry Magnetic inequivalence Hydride Cationic polymerization chemistry Hydrogenation Hydrogen |
| Zdroj: | Inorganic Chemistry. 48:663-670 |
| ISSN: | 1520-510X 0020-1669 |
| DOI: | 10.1021/ic8020029 |
| Popis: | The cationic iridium complexes [Ir(COD)(PR3)2]BF4 (1a-c) (a, R = Ph; b, R = p-tolyl; c, R = p-C6H4-OMe) react with parahydrogen in the presence of pyridine to give trans, cis, cis-[Ir(PR3)2(py)2(H)2]+ (2a-c) and small amounts of fac, cis-[Ir(PR3)(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 DeltaH(double dagger) = 134 +/- 1 kJ mol(-1) and DeltaS(double dagger) = 151 +/- 5 J mol(-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. |
| Databáze: | OpenAIRE |
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