A new route for the efficient metalation of unfunctionalized aromatics
| Autor: | Andrew J. Peel, Andrew E. H. Wheatley, Noriyuki Tezuka, James M. D'Rozario, Masanobu Uchiyama |
|---|---|
| Rok vydání: | 2019 |
| Předmět: |
010405 organic chemistry
Metalation Dimer General Chemistry Nuclear magnetic resonance spectroscopy 010402 general chemistry 01 natural sciences 0104 chemical sciences Chemistry Crystallography chemistry.chemical_compound Catenation Deprotonation chemistry Reactivity (chemistry) Bimetallic strip Two-dimensional nuclear magnetic resonance spectroscopy |
| Zdroj: | Chemical Science |
| ISSN: | 2041-6539 2041-6520 |
| Popis: | Efficient metalation of benzene is reported for the first time using reagents based only upon a mixture of a copper amide and a lithium amide. 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. |
| Databáze: | OpenAIRE |
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