Using coligands to gain mechanistic insight into iridium complexes hyperpolarized with para -hydrogen
Using coligands to gain mechanistic insight into iridium complexes hyperpolarized with para -hydrogen
复制标题
使用共配体获得对位氢超极化铱配合物的机理见解
DOI：
10.1039/c9sc00444k
复制
发表时间：
2019
期刊：
影响因子：
8.4
通讯作者：
Tickner B
中科院分区：
文献类型：
--
作者：
Tickner B
本文报道了一系列新的[Ir（H）_2（IMes）（α-13 C_2-羧基亚胺）L]配合物的形成，其中L的配体是不同的。当检查与仲氢，络合物中，L是苄胺或苯乙胺表现出显着的1H氢化物和13 C2亚胺增强，并可能存在于13 C2单重自旋顺序。同位素标记技术被用来加倍13 C2增强（高达750倍）和单重态寿命（高达20秒）相比，以前报道的。交换光谱和密度泛函理论被用来研究这些复合物中快速氢交换的稳定性和机制，这是一个由解离共配体损失驱动的过程，形成一个关键的五配位中间体。当L是吡啶或咪唑，竞争性结合到这样的中间体导致新的复合物的形成，动力学，行为，结构和超极化的研究。发现所观察到的PHIP增强的比率不仅受氢交换速率的影响，而且受共配体的身份的影响。这种配体反应性伴随着任何13 C2单线态顺序的退相干，其可以通过同位素标记来保存。添加硫醇共配体证明产生硫醇氧化加成产物，其特征在于通过NMR和MS技术。当使用α-羧基亚胺阻断活性配位位点时，使用可逆交换信号放大（SABRE）过程可以实现吡啶的显著870倍13 C增强。因此，[Ir（H）2（IMes）（α-13 C2-羧基亚胺）L]作为独特的传感器，其1H氢化物化学位移和相应的超极化水平指示共配体的身份及其结合强度。
We report the formation of a series of novel [Ir(H)2(IMes)(α-13C2-carboxyimine)L] complexes in which the identity of the coligand L is varied. When examined with para-hydrogen, complexes in which L is benzylamine or phenethylamine show significant 1H hydride and 13C2 imine enhancements and may exist in 13C2 singlet spin order. Isotopic labeling techniques are used to double 13C2 enhancements (up to 750-fold) and singlet state lifetimes (up to 20 seconds) compared to those previously reported. Exchange spectroscopy and Density Functional Theory are used to investigate the stability and mechanism of rapid hydrogen exchange in these complexes, a process driven by dissociative coligand loss to form a key five coordinate intermediate. When L is pyridine or imidazole, competitive binding to such intermediates leads to novel complexes whose formation, kinetics, behaviour, structure, and hyperpolarization is investigated. The ratio of the observed PHIP enhancements were found to be affected not only by the hydrogen exchange rates but the identity of the coligands. This ligand reactivity is accompanied by decoherence of any 13C2 singlet order which can be preserved by isotopic labeling. Addition of a thiol coligand proved to yield a thiol oxidative addition product which is characterized by NMR and MS techniques. Significant 870-fold 13C enhancements of pyridine can be achieved using the Signal Amplification By Reversible Exchange (SABRE) process when α-carboxyimines are used to block active coordination sites. [Ir(H)2(IMes)(α-13C2-carboxyimine)L] therefore acts as unique sensors whose 1H hydride chemical shifts and corresponding hyperpolarization levels are indicative of the identity of a coligand and its binding strength.