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![Measuring the Spin-Lattice Relaxation Magnetic Field Dependence of Hyperpolarized [1-13C]pyruvate](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F59399.jpg&w=3840&q=50)
Measuring the Spin-Lattice Relaxation Magnetic Field Dependence of Hyperpolarized [1-13C]pyruvate
Published on: September 13, 2019
Spontaneous transfer of parahydrogen derived spin order to pyridine at low magnetic field
Kevin D Atkinson1, Michael J Cowley, Paul I P Elliott
1Department of Chemistry, University of York, Heslington, York, YO10 5DD, United Kingdom.
Abstract:
The cationic iridium complex [Ir(COD)(PCy(3))(py)]BF(4) (1) is shown to react with dihydrogen in the presence of pyridine (py) to form the dihydride complex fac,cis-[Ir(PCy(3))(py)(3)(H)(2)]BF(4) (2). Complex 2 undergoes rapid exchange of the two bound pyridine ligands which are trans to hydride with free pyridine; the activation parameters for this process in methanol are DeltaH(double dagger) = 97.4 +/- 9 kJ mol(-1) and DeltaS(double dagger) = 84 +/- 31 J K(-1) mol(-1). When parahydrogen is employed as a source of nuclear spin polarization, spontaneous magnetization transfer proceeds in low magnetic field from the two nascent hydride ligands of 2 to its other NMR active nuclei. Upon interrogation by NMR spectroscopy in a second step, signal enhancements in excess of 100 fold are observed for the (1)H, (13)C and (15)N resonances of free pyridine after ligand exchange. The degree of signal enhancement in the free substrate is increased by employing electronically rich and sterically encumbered phosphine ligands such as PCy(3), PCy(2)Ph, or P(i)Pr(3) and by optimizing the strength of the magnetic field in which polarization transfer occurs.
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