Understanding the Electronic Factors Responsible for Ligand Spin-Orbit NMR Shielding in Transition-Metal Complexes.
Understanding the Electronic Factors Responsible for Ligand Spin-Orbit NMR Shielding in Transition-Metal Complexes.
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DOI：
10.1021/ct501089z
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发表时间：
2015-03
影响因子：
5.5
通讯作者：
J. Vícha;C. Foroutan‐Nejad;Tomasz Pawlak;M. Munzarová;M. Straka;R. Marek
中科院分区：
文献类型：
--
作者：
J. Vícha;C. Foroutan‐Nejad;Tomasz Pawlak;M. Munzarová;M. Straka;R. Marek
相对论效应在改变重元素化合物中轻核的NMR化学位移中的重要作用已经被认识了很长一段时间;然而，对这种现象与电子结构的关系的充分理解尚未实现。本文用Au配合物中6s和6p原子轨道的收缩解释了最近观察到的铂和金化合物在邻位轻原子（13）C，（15）N）σ（SO）（LA）处自旋轨道诱导（SO）核磁屏蔽的大小和符号上的定性差异。这是由于金配合物中Au的核电荷较大，标量相对论效应较强。这导致了Au配合物中金属6s和6p原子轨道的化学活化以及它们与配体的更大参与键合，这通过自旋轨道/费米接触（SO/FC）机制调节了金属诱导的SO效应对LA的NMR信号的传播。这些正方形平面配合物中的σ（SO）（LA）的大小可以基于各种金属基5d → 5d* 和6p → 6p* 轨道磁耦合之间的平衡来理解。铂配合物中大的正的σ（SO）（LA）主要是由屏蔽的铂基5d → 5d* 磁耦合所决定的，而金配合物中小的或负的σ（SO）（LA）则与金基6p → 6p* 磁耦合的去屏蔽贡献有关。此外，它表明，σ（SO）（LA）与M-LA电子共享的程度，即共价的M-LA键（由QTAIM离域指数，DI表征）定量相关。本研究结果将有助于进一步理解影响重元素系统实验NMR参数的相对论效应的起源和传播。
The significant role of relativistic effects in altering the NMR chemical shifts of light nuclei in heavy-element compounds has been recognized for a long time; however, full understanding of this phenomenon in relation to the electronic structure has not been achieved. In this study, the recently observed qualitative differences between the platinum and gold compounds in the magnitude and the sign of spin-orbit-induced (SO) nuclear magnetic shielding at the vicinal light atom ((13)C, (15)N), σ(SO)(LA), are explained by the contractions of 6s and 6p atomic orbitals in Au complexes, originating in the larger Au nuclear charge and stronger scalar relativistic effects in gold complexes. This leads to the chemical activation of metal 6s and 6p atomic orbitals in Au complexes and their larger participation in bonding with the ligand, which modulates the propagation of metal-induced SO effects on the NMR signal of the LA via the Spin-Orbit/Fermi Contact (SO/FC) mechanism. The magnitude of the σ(SO)(LA) in these square-planar complexes can be understood on the basis of a balance between various metal-based 5d → 5d* and 6p → 6p* orbital magnetic couplings. The large and positive σ(SO)(LA) in platinum complexes is dominated by the shielding platinum-based 5d → 5d* magnetic couplings, whereas small or negative σ(SO)(LA) in gold complexes is related to the deshielding contribution of the gold-based 6p → 6p* magnetic couplings. Further, it is demonstrated that σ(SO)(LA) correlates quantitatively with the extent of M-LA electron sharing that is the covalence of the M-LA bond (characterized by the QTAIM delocalization index, DI). The present findings will contribute to further understanding of the origin and propagation of the relativistic effects influencing the experimental NMR parameters in heavy-element systems.