Self-assembly processes of highly reduced corannulene generated by the chemical reduction with a binary combination of alkali metals, namely Li/K and Li/Rb, have been investigated by a synergistic use of NMR spectroscopy, X-ray crystallography and DFT calculations. The formation of several unique mixed metal core sandwich-type products based on tetrareduced corannulene, C20H104-, has been revealed. According to the X-ray diffraction studies, these remarkable triple-decker supramolecular aggregates illustrate a record ability of bowl-shaped and highly charged corannulene to provide all its sites, five benzene rings fused to a central five-membered ring, for binding of six alkali metal ions. The previously unseen engagement of the hub-site of C20H104− in lithium binding is accompanied by unprecedented shifts up to –25 ppm in 7Li NMR spectra. The theoretical analysis of these unique systems now provides an explanation for such record shifts for the centrally located lithium ion. Furthermore, the analysis of X-ray diffraction data allows us to correlate the NMR shifts with structures of the sandwich-type assemblies and to show that the 7Li NMR signal from the internal lithium ion could be used for qualitative evaluation of the interaction strength between the charged bowls in organometallic supramolecular aggregates.

Structural trends for triple-decker organometallic sandwiches formed by highly charged π-bowls with mixed alkali metal cores: Li/K vs. Li/Rb

249th National Meeting (2015)

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