The metallation reaction (transforming an inert C-H bond to a labile, more synthetically pliable C-metal bond) is one of the core tools of synthetic chemistry, widely employed in academic laboratories and in fine chemical and pharmaceutical manufacture. If lithium alkyls and lithium amides are regarded as first generation metallating agents, then currently a second generation is emerging in which co-operative effects between different components, often a metal amide combined with an organometallic compound or a metal salt, lead to reactivities and selectivities beyond the scope of conventional single-metal reagents.Some of this bimetallic-executed metallation chemistry can be described as a black art since the nature of the metallating species as well as the structures and mechanisms involved are not generally well understood. Here, after presenting some key examples of the benefits of using such bimetallic reagents, we try to clarify some of these aspects by reporting new structurally characterised bimetallic reagents. We show that their seemingly simple metal-hydrogen exchange reactions with aromatic substrates are manifested through complex inverse crown arrangements. Using NMR spectroscopic studies (including DOSY experiments) we also ponder the question whether such reactions are genuinely bimetallic in execution or alternatively occur through two step monometallation-second metal trapping processes.

Deconvoluting the black art of metallation: Understanding the benefits of placing two metals in the synthetic chemists' palette

247th National Meeting (2014)

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