Issue 3, 2015

Self-assembly of tetrareduced corannulene with mixed Li–Rb clusters: dynamic transformations, unique structures and record 7Li NMR shifts

Abstract

Self-assembly processes of the highly reduced bowl-shaped corannulene generated by the chemical reduction with a binary combination of alkali metals, namely Li–Rb, have been investigated by variable-temperature 1H and 7Li NMR spectroscopy. The formation of several unique mixed metal sandwich products based on tetrareduced corannulene, C20H104− (14−), has been revealed followed by investigation of their dynamic transformations in solutions. Analysis of NMR data allowed to propose the mechanism of stepwise alkali metal substitution as well as to identify experimental conditions for the isolation of intermediate and final supramolecular products. As a result, two new triple-decker aggregates with a mixed Li–Rb core, [{Rb(THF)2}2]//[Li3Rb2(C20H10)2{Li+(THF)}] (2) and [{Rb(diglyme)}2]//[Li3Rb3(C20H10)2(diglyme)2]·0.5THF (3·0.5THF), have been crystallized and structurally characterized. The Li3Rb2-product has an open coordination site at the sandwich periphery and thus is considered transient on the way to the Li3Rb3-sandwich having the maximized intercalated alkali metal content. Next, the formation of the LiRb5 self-assembly with 14− has been identified by 7Li NMR as the final step in a series of dynamic transformations in this system. This product was also isolated and crystallographically characterized to confirm the LiRb5 core. Notably, all sandwiches have their central cavities, located in between the hub-sites of two C20H104− decks, occupied by an internal Li+ ion which exhibits the record high negative shift (ranging from −21 to −25 ppm) in 7Li NMR spectra. The isolation of three novel aggregates having different Li–Rb core compositions allowed us to look into the origin of the unusual 7Li NMR shifts at the molecular level. The discussion of formation mechanisms, dynamic transformations as well as unique electronic structures of these remarkable mixed alkali metal organometallic self-assemblies is provided and supported by DFT calculations.

Graphical abstract: Self-assembly of tetrareduced corannulene with mixed Li–Rb clusters: dynamic transformations, unique structures and record 7Li NMR shifts

Supplementary files

Article information

Article type
Edge Article
Submitted
11 Nov 2014
Accepted
16 Dec 2014
First published
16 Dec 2014
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2015,6, 1959-1966

Self-assembly of tetrareduced corannulene with mixed Li–Rb clusters: dynamic transformations, unique structures and record 7Li NMR shifts

A. S. Filatov, S. N. Spisak, A. V. Zabula, J. McNeely, A. Yu. Rogachev and M. A. Petrukhina, Chem. Sci., 2015, 6, 1959 DOI: 10.1039/C4SC03485F

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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