Abstract
The cationic iridium complex [Ir(COD)(PCy3)(py)]BF4 (1) is shown to react with dihydrogen in the presence of pyridine (py) to form the dihydride complex fac,cis[Ir(PCy3)(Py)(3)(H)(2)]BF4 (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 Delta H double dagger = 97.4 +/- 9 kJ mol(-1) and Delta S double dagger = 84.3 +/- 1 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 H-1, C-13 and N-15 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 PCy3, PCy2Ph, or (PPr3)-Pr-i and by optimizing the strength of the Magnetic field in which polarization transfer occurs.
| Original language | English |
|---|---|
| Pages (from-to) | 13362-13368 |
| Number of pages | 7 |
| Journal | Journal of the American Chemical Society |
| Volume | 131 |
| Issue number | 37 |
| DOIs | |
| Publication status | Published - 23 Sept 2009 |
Keywords
- PARA-HYDROGEN
- INDUCED POLARIZATION
- PASADENA HYPERPOLARIZATION
- CATALYTIC-HYDROGENATION
- NMR-SPECTROSCOPY
- NOBEL LECTURE
- MRI
- ALIGNMENT
- STATE
- TIMES