Diamagnetic Group 6 Tetrakis(di-tert-butylketimido)metal(IV) Complexes

The addition of 4 equiv of LiNC-t-Bu2 to CrCl3, MoCl5, and WCl6 in diethyl ether produced the complexes M(NC-t-Bu2)4 (M = Cr, Mo, W). Single-crystal X-ray diffraction studies revealed that the molecules have flattened tetrahedral geometries with virtual D2d symmetry in the solid state. 1H and 13C NMR spectra indicated that the complexes are diamagnetic, and a qualitative MO analysis showed that the orthogonal π-donor and -acceptor orbitals of the ketimide ligand cooperatively split the dxy and dz2 orbitals sufficiently to allow spin pairing in the dxy orbital. A more sophisticated quantum-mechanical analysis of Cr(NC-t-Bu2)4 using density functional/molecular mechanics methods confirmed the qualitative analysis by showing that the singlet state is 27 kcal/mol more stable than the triplet state.

向二乙醚中的CrCl3、MoCl5和WCl6中添加4摩尔当量的LiN(C-t-Bu2)后，生成了M(N(C-t-Bu2))4 (M分别为Cr、Mo、W)的配合物。单晶X射线衍射研究表明，这些分子在固态下具有展平的四面体几何结构，并呈现出虚拟的D2d对称性。1H和13C核磁共振光谱表明，这些配合物为抗磁性，定性分子轨道分析显示，酮亚胺配体的正交π供体和受体轨道协同分裂dxy和dz2轨道，使其足以允许dxy轨道中的自旋配对。采用密度泛函/分子力学方法对Cr(N(C-t-Bu2))4进行的高级量子力学分析，通过证实单线态比三线态稳定27 kcal/mol，进一步证实了定性分析的结果。