Spontaneous Transfer of Parahydrogen Derived Spin Order to Pyridine at Low Magnetic Field

详细信息    查看全文

• 作者：Kevin D. Atkinson ; Michael J. Cowley ; Paul I. P. Elliott ; Simon B. Duckett ; Gary G. R. Green ; Joaqun Lpez-Serrano ; Adrian C. Whitwood
• 刊名：Journal of the American Chemical Society
• 出版年：2009
• 出版时间：September 23, 2009
• 年：2009
• 卷：131
• 期：37
• 页码：13362-13368
• 全文大小：233K
• 年卷期：v.131,no.37(September 23, 2009)
• ISSN：1520-5126

文摘

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 ΔH = 97.4 ± 9 kJ mol⁻¹ and ΔS = 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 ¹H, ¹³C and ¹⁵N 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 PⁱPr₃ and by optimizing the strength of the magnetic field in which polarization transfer occurs.