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Issue 11, 2019
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A new route for the efficient metalation of unfunctionalized aromatics

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Abstract

The synthesis and isolation of a novel bimetallic species formed by reacting two equivalents of TMPLi with CuCl in the presence of Et2O are reported. X-ray crystallography reveals the Et2O-free tetranuclear aggregate (TMPCu)2(TMPLi)21, which formally results from the catenation of dimers of TMPLi and TMPCu. NMR spectroscopy confirms that, upon dissolution in hydrocarbon media, the crystals fail to form a conventional Gilman cuprate dimer. Instead they exhibit a spectrum which is consistent with that recently proposed for an isomer of dimeric Gilman cuprate. Moreover, while pre-isolated Gilman cuprate is inert to benzene solvent, this new isomer smoothly affects aromatic deprotonation to give mainly Ph(TMP)3Cu2Li23, which is formally a heterodimer of Gilman cuprate TMPCu(μ-TMP)Li 2 and PhCu(μ-TMP)Li 4. Attempts to synthesise 3 through explicit combination of pre-isolated 2 and 4 were successful; additionally, this permitted the preparation of Ph(TMP)3Cu3Li 5 and Ph(TMP)3CuLi37 when 4 was combined in 1 : 2 ratios with TMPCu or TMPLi, respectively. 5 was characterised as metallacyclic in the solid-state, its structural features resembling those in 3 but with reduced Li–π interactions. It also proved possible to perform Cu/Li exchange on 5 (using tBuOCu) to give a novel mixed organo(amido)copper species Ph(TMP)3Cu46. Remarkably, the unprecedented reactivity of 1 towards benzene is reproduced by heating a 1 : 1 mixture of TMPLi and TMPCu in the same solvent; this gives predominantly 3. On the other hand, mixtures which are rich in either Cu or Li can lead to the selective in situ formation of 5 or 7. Though crystallographic data on 7 could not be obtained, DFT calculations accurately corroborated the observed structures of 3 and 5 and could be used to support 7 having the same structure type, albeit with enhanced Li–π interactions. This was consistent with NMR spectroscopic data. However, in contrast to 3 and 5, for which 2D NMR spectroscopy indicated only conformational changes, 7 was additionally found to exhibit fluxionality in a manner consistent with a dissociative process.

Graphical abstract: A new route for the efficient metalation of unfunctionalized aromatics

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Supplementary files

Article information


Submitted
28 Sep 2018
Accepted
01 Feb 2019
First published
05 Feb 2019

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2019,10, 3385-3400
Article type
Edge Article

A new route for the efficient metalation of unfunctionalized aromatics

A. J. Peel, N. Tezuka, J. M. D'Rozario, M. Uchiyama and A. E. H. Wheatley, Chem. Sci., 2019, 10, 3385
DOI: 10.1039/C8SC04325F

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