Hyperpolarisation through reversible interactions with parahydrogen
Hyperpolarisation through reversible interactions with parahydrogen
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DOI：
10.1039/c4cy00464g
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发表时间：
2014-01-01
影响因子：
5
通讯作者：
Ruddlesden, Amy J.
中科院分区：
文献类型：
--
作者：
Lloyd, Lyrelle S.;Asghar, Aziz;Ruddlesden, Amy J.
我们在这里描述了络合物Ir（COD）（NHC）Cl [NHC = IMes、SIMes、IPr、SIPr、ICy、IMe和ImMe（2）NPr（2）（i）]如何提供对催化过程的重要洞察，该催化过程支持通过可逆交换的超极化方法信号放大（SABRE）。这些配合物与吡啶和H-2反应生成[Ir（H）（2）（NHC）（py）（3）]Cl，其在与用于可逆交换效应的信号放大的良好催化活性相称的时间尺度上进行配体交换。这种活性是由氢化物配体的磁性不等价性引起的，并且高度依赖于NHC。变温和动力学研究表明，位于0.1和0.5 s（-1）之间的配体损失率是理想的催化。溶剂络合物[Ir（H）（2）（MeOH）（NHC）（py）（2）]Cl在配体交换途径中的作用被揭示，该络合物含有化学上不等价的氢化物配体。通过优化条件和NHC，当NHC是IMes时，揭示了5500倍的总吡啶信号增强。T-1-还原效应和HD与溶剂的交换被探测并显示与催化剂效率有关。由此产生的信号增强表明，未来在生理条件下使用这种催化效应的体内MRI测量将是可能的。
We describe here how the complexes Ir(COD)(NHC)Cl [NHC = IMes, SIMes, IPr, SIPr, ICy, IMe and ImMe(2)NPr(2)(i)] provide significant insight into the catalytic process that underpins the hyperpolarization method signal amplification by reversible exchange (SABRE). These complexes react with pyridine and H-2 to produce [Ir(H)(2)(NHC)(py)(3)]Cl which undergo ligand exchange on a timescale commensurate with good catalytic activity for the signal amplification by reversible exchange effect. This activity results from hydride ligand magnetic inequivalence and is highly dependent on the NHC. Variable temperature and kinetic studies demonstrate that rates of ligand loss which lie between 0.1 and 0.5 s(-1) are ideal for catalysis. A role for the solvent complex [Ir(H)(2)(MeOH)(NHC)(py)(2)]Cl, which contains chemically inequivalent hydride ligands is revealed in the ligand exchange pathway. By optimisation of the conditions and NHC, a 5500-fold total pyridine signal enhancement is revealed when the NHC is IMes. Both T-1-reduction effects and HD exchange with the solvent are probed and shown to link to catalyst efficiency. The resulting signal enhancements suggest future in vivo MRI measurements under physiological conditions using this catalytic effect will be possible.