American Chemical Society
ja108265y_si_002.cif (22.94 kB)

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

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posted on 2010-12-29, 00:00 authored by Rosanna A. D. Soriaga, Jennifer M. Nguyen, Thomas A. Albright, David M. Hoffman
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.