Greif Anja H, Hrobárik Peter, Autschbach Jochen, Kaupp Martin
Institut für Chemie, Technische Universität Berlin, Strasse des 17. Juni 135, D-10623 Berlin, Germany.
Department of Chemistry, University at Buffalo, State University of New York, Buffalo, NY 14260, USA.
Phys Chem Chem Phys. 2016 Nov 9;18(44):30462-30474. doi: 10.1039/c6cp06129j.
Previous relativistic quantum-chemical predictions of unusually large H and C NMR chemical shifts for ligand atoms directly bonded to a diamagnetic uranium(vi) center (P. Hrobárik, V. Hrobáriková, A. H. Greif and M. Kaupp, Angew. Chem., Int. Ed., 2012, 51, 10884) have been revisited by two- and four-component relativistic density functional methods. In particular, the effect of the exchange-correlation response kernel, which had been missing in the previously used two-component version of the Amsterdam Density Functional program, has been examined. Kernel contributions are large for cases with large spin-orbit (SO) contributions to the NMR shifts and may amount to up to ∼30% of the total shifts, which means more than a 50 ppm difference for the metal-bonded carbon shifts in some extreme cases. Previous calculations with a PBE-40HF functional had provided overall reasonable predictions, due to cancellation of errors between the missing kernel contributions and the enhanced exact-exchange (EXX) admixture of 40%. In the presence of an exchange-correlation kernel, functionals with lower EXX admixtures give already good agreement with experiments, and the PBE0 functional provides reasonable predictive quality. Most importantly, the revised approach still predicts unprecedented giant H NMR shifts between +30 ppm and more than +200 ppm for uranium(vi) hydride species. We also predict uranium-bonded C NMR shifts for some synthetically known organometallic U(vi) complexes, for which no corresponding signals have been detected to date. In several cases, the experimental lack of these signals may be attributed to unexpected spectral regions in which some of the C NMR shifts can appear, sometimes beyond the usual measurement area. An extremely large uranium-bonded C shift above 550 ppm, near the upper end of the diamagnetic C shift range, is predicted for a known pincer carbene complex. Bonding analyses allow in particular the magnitude of the SO shifts, and of their dependence on the functional, on the ligand position in the complex, and on the overall electronic structure to be better appreciated, and improved confidence ranges for predicted shifts have been obtained.
先前关于直接与抗磁性铀(VI)中心键合的配体原子具有异常大的氢和碳核磁共振化学位移的相对论量子化学预测(P. Hrobárik、V. Hrobáriková、A. H. Greif和M. Kaupp,《德国应用化学》,国际版,2012年,第51卷,10884页)已通过二分量和四分量相对论密度泛函方法重新研究。特别是,研究了先前使用的阿姆斯特丹密度泛函程序的二分量版本中缺失的交换相关响应核的影响。对于自旋轨道(SO)对核磁共振位移贡献较大的情况,核贡献很大,可能高达总位移的约30%,这意味着在某些极端情况下,金属键合碳位移的差异超过50 ppm。先前使用PBE - 40HF泛函的计算提供了总体合理的预测,这是由于缺失的核贡献与40%的增强精确交换(EXX)混合之间的误差相互抵消。在存在交换相关核的情况下,EXX混合较低的泛函已经与实验结果有很好的一致性,并且PBE0泛函提供了合理的预测质量。最重要的是,修订后的方法仍然预测铀(VI)氢化物物种的氢核磁共振位移在+30 ppm至超过+200 ppm之间,这是前所未有的巨大位移。我们还预测了一些合成已知的有机金属U(VI)配合物的铀键合碳核磁共振位移,迄今为止尚未检测到相应的信号。在几种情况下,实验中未检测到这些信号可能归因于一些碳核磁共振位移可能出现的意外光谱区域,有时超出了通常的测量范围。对于一种已知的钳形卡宾配合物,预测其铀键合碳位移极大,超过550 ppm,接近抗磁性碳位移范围的上限。键合分析尤其有助于更好地理解自旋轨道位移的大小、其对泛函的依赖性、对配合物中配体位置的依赖性以及对整体电子结构的依赖性,并且已经获得了预测位移的改进置信范围。