The past few years have witnessed a dramatic change in the landscape of aromatic deprotonative metallation chemistry (conversion of a relatively inert sp2-C-H bond to a reactive, more synthetically useful C-metal bond). Whereas previously only lithium alkyls and lithium amides have generally been capable of executing such challenging metallation reactions, recent studies have seen a growth of a forest of new metallating agents based on ate formulations, especially magnesiates, zincates and aluminates. Aluminates are particularly attractive bases due to the comparative cheapness, low toxicity and recycling opportunities of aluminium, the most abundant metal in the earth's crust. While several reports have established the excellent regio- and chemo-selectivity of lithium TMP-aluminates (TMP is 2,2,6,6-tetramethylpiperidide) in deprotonation reactions of substituted aromatic compounds, the nature of the active base species in these multicomponent solution mixtures is still open to question. In reporting a combination of reactivity studies, X-ray crystallographic characterisations, multinuclear NMR (including DOSY) experiments and DFT calculations, this presentation seeks an answer to the key question, �does aluminium or lithium execute the C-H to C-metal transformation in these reactions?� On the precedents of earlier studies the answer is surprising.

TMP-aluminates: Bases or bystanders in aromatic C-H deprotonation reactions?

248th National Meeting (2014)

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