The Tricarbonylchromium Complex of a Trimethyltin-Substitued N‑(Triisopropylsilyl)indole - A Dynamic NMR Study of Multiple Independent Rotation Processes in the Solid State with an X-ray Diffraction Structure and Molecular Mechanics Calculations. Aliev, A. E.; Anderson, J. E.; Butler, D.; Gonzalez-Quteirino, J.; Lunazzi, L.; Mazzanti, A.; Steed, J. W.; Wilhelm, R. Eur. J. Inorg. Chem. 2002, 133-140.
Abstract: The title compound was studied by dynamic NMR spectroscopy in solution and in the solid state, and by MM3 molecular mechanics calculations of model compounds. Barriers to rotation of the trimethyltin group, the tricarbonylchromium group, the triisopropylsilyl group, and the isopropyl groups were all too small to measure by NMR in solution i.e. less than about 5 kcal/mol. All of these barriers could be measured, however, in the solid state, are of different sizes, and are surprisingly large, up to 12.9 kcal/mol. A crystal structure determination shows close intermolecular interactions of these triple rotors that explain these high rotation barriers.