Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 1-5, 8093, Zürich, Switzerland.
Institut Charles Gerhardt, UMR 5253 CNRS, cc 1501, Université de Montpellier, Place. E. Bataillon, 34095, Montpellier, France.
Angew Chem Int Ed Engl. 2017 Aug 14;56(34):10127-10131. doi: 10.1002/anie.201701537. Epub 2017 Jun 7.
Fischer and Schrock carbenes display highly deshielded carbon chemical shifts (>250 ppm), in particular Fischer carbenes (>300 ppm). Orbital analysis of the principal components of the chemical shift tensors determined by solid-state NMR spectroscopy and calculated by a 2-component DFT method shows specific patterns that act as fingerprints for each type of complex. The calculations highlight the role of the paramagnetic term in the shielding tensor especially in the two most deshielded components (σ and σ ). The paramagnetic term of σ is dominated by coupling σ(M=C) with π*(M=C) through the angular momentum operator perpendicular to the σ and π M=C bonds. The highly deshielded carbon of Fischer carbenes results from the particularly low-lying π*(M=C) associated with the CO ligand. A contribution of the coupling of π(M=C) with σ*(M=C) is found for Schrock and Ru-based carbenes, indicating similarities between them, despite their different electronic configurations (d vs. d ).
菲舍尔卡宾和肖罗克卡宾的碳化学位移具有高度去屏蔽效应（>250 ppm），特别是菲舍尔卡宾（>300 ppm）。通过固态 NMR 光谱测定和通过双组分 DFT 方法计算的化学位移张量主分量的轨道分析显示出特定的模式，这些模式可作为每种类型配合物的特征指纹。这些计算突出了屏蔽张量中顺磁项的作用，特别是在两个去屏蔽程度最大的分量（σ 和 σ ）中。σ 中顺磁项主要通过垂直于 σ 和 π M=C 键的角动量算子与 M=C 上的 σ 和 π*（M=C）进行耦合。菲舍尔卡宾碳原子具有高度去屏蔽效应，是因为与 CO 配体相关的π*（M=C）特别低。肖罗克卡宾和基于 Ru 的卡宾也发现了π*（M=C）与 σ*（M=C）之间的耦合贡献，这表明它们之间存在相似性，尽管它们具有不同的电子构型（d 与 d ）。
