Crystal Packing Induced Carbon–Carbon Double–Triple Bond Isomerization in a Zirconocene Complex

Abstract

We present a combined theoretical and experimental analysis of the carbon–carbon bond character in two prototypical zirconocene complexes. The two cyclic seven-membered ring zirconium compounds 2a and 2b differ by the substitution of a tert-butyl by a trimethylsilyl group. Due to the coordination of the π-system to the metal atom, a formally forbidden (η2-allenyl)/enamido-Zr to (η2-alkyne)/κN-imine-Zr complex isomerization is feasible. State-of-the-art dispersion-corrected density functional theory (DFT-D3) is used in both the solid and condensed phase to examine and quantify the experimental structures (X-ray diffraction) and 13C NMR magnetic shielding. The complementary investigations demonstrate the importance of nonlocal London dispersion interactions. Both X-ray structures agree excellently with the results of the solid-state DFT-D3 calculations. Interestingly, 2b exhibits a mixed allene–alkyne form in the solid state, while its gas phase structure has a strong allene character. The substitution lead...