title: Para-hydrogen induced polarization without incorporation of para-hydrogen into the analyte.
abstract: 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.
authors.affiliation: Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Atkinson
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Cowley
authors.forename: Simon B
authors.initials: SB
authors.lastname: Duckett
authors.forename: Paul I P
authors.initials: PI
authors.lastname: Elliott
authors.forename: Gary G R
authors.initials: GG
authors.lastname: Green
authors.forename: Joaquín
authors.initials: J
authors.lastname: López-Serrano
authors.forename: Iman G
authors.initials: IG
authors.lastname: Khazal
authors.forename: Adrian C
authors.initials: AC
authors.lastname: Whitwood
mesh_terms: D018360:Crystallography, X-Ray; D034242:Cyclooctanes / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry*; D006865:Hydrogenation; D007495:Iridium / Q000737:chemistry; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008280:Magnetics; D009584:Nitrogen / Q000737:chemistry; D009942:Organometallic Compounds / Q000737:chemistry; D010720:Phosphines / Q000737:chemistry; D011725:Pyridines / Q000737:chemistry
chemical_list: C411867:1,3-cyclooctadiene; D034242:Cyclooctanes; D008024:Ligands; D009942:Organometallic Compounds; D010720:Phosphines; D011725:Pyridines; D007495:Iridium; D006859:Hydrogen; C044646:phosphine; D009584:Nitrogen; C023666:pyridine