A new route for the efficient metalation of unfunctionalized aromatics.

The synthesis and isolation of a novel bimetallic species formed by reacting two equivalents of TMPLi with CuCl in the presence of EtO are reported. X-ray crystallography reveals the EtO-free tetranuclear aggregate (TMPCu)(TMPLi) , 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 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)CuLi , which is formally a heterodimer of Gilman cuprate TMPCu(μ-TMP)Li and PhCu(μ-TMP)Li . Attempts to synthesise through explicit combination of pre-isolated and were successful; additionally, this permitted the preparation of Ph(TMP)CuLi and Ph(TMP)CuLi when was combined in 1 : 2 ratios with TMPCu or TMPLi, respectively. was characterised as metallacyclic in the solid-state, its structural features resembling those in but with reduced Li-π interactions. It also proved possible to perform Cu/Li exchange on (using BuOCu) to give a novel mixed organo(amido)copper species Ph(TMP)Cu . Remarkably, the unprecedented reactivity of towards benzene is reproduced by heating a 1 : 1 mixture of TMPLi and TMPCu in the same solvent; this gives predominantly . On the other hand, mixtures which are rich in either Cu or Li can lead to the selective formation of or . Though crystallographic data on could not be obtained, DFT calculations accurately corroborated the observed structures of and and could be used to support having the same structure type, albeit with enhanced Li-π interactions. This was consistent with NMR spectroscopic data. However, in contrast to and , for which 2D NMR spectroscopy indicated only conformational changes, was additionally found to exhibit fluxionality in a manner consistent with a dissociative process.