Iridium(III) hydrido N-heterocyclic carbene-phosphine complexes as catalysts in magnetization transfer reactions.
Iridium(III) hydrido N-heterocyclic carbene-phosphine complexes as catalysts in magnetization transfer reactions.
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DOI：
10.1021/ic401783c
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发表时间：
2013-12-02
影响因子：
4.6
通讯作者：
Whitwood A
中科院分区：
文献类型：
--
作者：
Fekete M;Bayfield OW;Duckett SB;Hart S;Mewis RE;Pridmore N;Rayner PJ;Whitwood A
超极化(HP)方法的可逆交换信号放大(SABRE)使用对氢来敏化核磁共振底物检测。[Ir(H)2(Imes)(MeCN)2(R)]BF4和[Ir(H)2(Imes)(Py)2(R)]BF4[Py=吡啶；R=Pcy3或PPh3；Imes=1，3-bis(2，4，6-trimethylphenyl)imidazol-2-ylidene]，同时含有给电子性的N-杂环卡宾和膦，用于催化SABRE。它们与乙腈和吡啶反应生成[Ir(H)2(NCMe)(Py)(Imes)(PPh3)]BF4和[Ir(H)2(NCMe)(Py)(Imes)(PCy3)]BF4，它们在与观察到的军刀效应相称的时间尺度上进行配体交换，这里通过对吡啶和乙腈HP的观察来说明这一点。在这项研究中，支持SABRE所需的对称破缺是通过使用化学不等价而不是先前报道的磁性不等价来提供的。因此，我们证明了极化转移催化剂的配位体本身变得超极化，因此高灵敏度地检测一些反应中间体是可能的。这些物种包括[Ir(H)2(NCMe)(Py)(Imes)(PPh3)]BF4、[Ir(H)2(MeOH)(Py)(Imes)(PPh3)]BF4和[Ir(H)2(NCMe)(Py)2(PPh3)]BF4。本文还描述了使用氚标记底物CD3CN和C5D5N以及标记配体P(C6D5)3和IMES-D22的研究，以证明减少质子稀释从而减少极化损耗可以显著提高HP水平。通过将这些研究与样品在极化转移点所经历的磁场变化的实验相结合，实现了对共振分配的确认。此外，当检查[Ir(H)2(pyridine-h5)(pyridine-d5)(IMes)(PPh3)]BF4时，其氢化物配体信号通过对氢诱导的极化而不是SABRE显示为可见的。对氢能够通过可逆交换的信号放大来对反应中间体进行核磁共振表征。
The hyperpolarization (HP) method signal amplification by reversible exchange (SABRE) uses para-hydrogen to sensitize substrate detection by NMR. The catalyst systems [Ir(H)2(IMes)(MeCN)2(R)]BF4 and [Ir(H)2(IMes)(py)2(R)]BF4 [py = pyridine; R = PCy3 or PPh3; IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene], which contain both an electron-donating N-heterocyclic carbene and a phosphine, are used here to catalyze SABRE. They react with acetonitrile and pyridine to produce [Ir(H)2(NCMe)(py)(IMes)(PPh3)]BF4 and [Ir(H)2(NCMe)(py)(IMes)(PCy3)]BF4, complexes that undergo ligand exchange on a time scale commensurate with observation of the SABRE effect, which is illustrated here by the observation of both pyridine and acetonitrile HP. In this study, the required symmetry breaking that underpins SABRE is provided for by the use of chemical inequivalence rather than the previously reported magnetic inequivalence. As a consequence, we show that the ligand sphere of the polarization transfer catalyst itself becomes hyperpolarized and hence that the high-sensitivity detection of a number of reaction intermediates is possible. These species include [Ir(H)2(NCMe)(py)(IMes)(PPh3)]BF4, [Ir(H)2(MeOH)(py)(IMes)(PPh3)]BF4, and [Ir(H)2(NCMe)(py)2(PPh3)]BF4. Studies are also described that employ the deuterium-labeled substrates CD3CN and C5D5N, and the labeled ligands P(C6D5)3 and IMes-d22, to demonstrate that dramatically improved levels of HP can be achieved as a consequence of reducing proton dilution and hence polarization wastage. By a combination of these studies with experiments in which the magnetic field experienced by the sample at the point of polarization transfer is varied, confirmation of the resonance assignments is achieved. Furthermore, when [Ir(H)2(pyridine-h5)(pyridine-d5)(IMes)(PPh3)]BF4 is examined, its hydride ligand signals are shown to become visible through para-hydrogen-induced polarization rather than SABRE. para-Hydrogen enables NMR characterization of the reaction intermediates via signal amplification by reversible exchange.
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影响因子：
4.9
作者：
Heinrich, H;Giernoth, R;Brown, JM
通讯作者：
Brown, JM
影响因子：
3.3
作者：
Kovtunov, Kirill V.;Beck, Irene E.;Koptyug, Igor V.
通讯作者：
Koptyug, Igor V.
DOI：
10.1007/s10334-013-0366-7
发表时间：
2013-10-01
影响因子：
2.3
作者：
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通讯作者：
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影响因子：
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作者：
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影响因子：
7.4
作者：
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通讯作者：
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