A new route for the efficient metalation of unfunctionalized aromaticsElectronic supplementary information (ESI) available. CCDC 1869336-1869340. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c8sc04325f

The synthesis and isolation of a novel bimetallic species formed by reacting two equivalents of TMPLi with CuCl in the presence of Et 2 O are reported. X-ray crystallography reveals the Et 2 O-free tetranuclear aggregate (TMPCu) 2 (TMPLi) 2 1 , 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) 3 Cu 2 Li 2 3 , 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) 3 Cu 3 Li 5 and Ph(TMP) 3 CuLi 3 7 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 t BuOCu) to give a novel mixed organo(amido)copper species Ph(TMP) 3 Cu 4 6 . 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. 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.