Structure and Dynamics of Homoleptic Beryllocenes: A Solid-State 9Be and 13C NMR Study

✍ Scribed by Ivan Hung; Charles L. B. Macdonald; Robert W. Schurko

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 473 KB
• Volume: 10
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/chem.200400404

✦ Synopsis

Abstract

The correlation between anisotropic ^9^Be NMR (quadrupolar and chemical shielding) interactions and the structure and dynamics in [Cp~2~Be], [${{\rm Cp}{{\ast \hfill \atop 2\hfill}}}$Be], and [(C~5~Me~4~H)~2~Be] is examined by solid‐state ^9^Be NMR spectroscopy, as well as by ab initio and hybrid density functional theory calculations. The ^9^Be quadrupole coupling constants in the three compounds correspond well to the relative degrees of spherical ground‐state electronic symmetry of the environment about beryllium. Theoretical computations of NMR interaction tensors are in excellent agreement with experimental values and aid in understanding the origins of NMR interaction tensors and their correlation to molecular symmetry. Variable‐temperature (VT) ^9^Be and ^13^C NMR experiments reveal a highly fluxional structure in the condensed phase of [Cp~2~Be]. In particular, the pathway by which the Cp rings of [Cp~2~Be] ‘invert’ coordination modes is examined in detail using hybrid density functional theory in order to inspect variations of the ^9^Be NMR interaction tensors. The activation energy for the ‘inversion’ process is found to be 36.9 kJ mol^−1^ from chemical exchange analysis of ^13^C VT CP/MAS NMR spectra. The low‐temperature (ca. −100 °C) X‐ray crystal structures of all three compounds have been collected and refined, and are in agreement with previously reported structures. In addition, the structure of the same Cp~2~Be crystal was determined at 20 °C and displays features consistent with increased intramolecular motion, supporting observations by ^9^Be VT NMR spectroscopy.