When the Ferrocene Analogy Breaks Down: Metallocene Transmetallation Chemistry

Ferrocene 1 and its dianionic Fe(bis)(dicarbollide) analogue 2 are classical compounds that display unusual stability. These compounds are not known to undergo transmetallation chemistry of the Fe-center and have been used extensively as chemical building blocks with consistent integrity. In this manuscript we describe the preparation of a charge compensated Fe(bis)(dicarbollide) species 3 Fe and its unprecedented transmetallation chemistry to Ir. Such reactions are hitherto unknown for any transition metal metallocene or metallacarborane complex. Additionally, we show that 3 Fe can be deprotonated to afford the corresponding bis(NHC) Li-carbenoid 5 that also displays unique reactivity. When 5 is reacted with [Ir(COD)Cl]2 it also undergoes a rapid transmetallation of the ferrocene "like" core to afford 6 but with the added twist that the Li-carbenoid moiety stays intact and does not transmetalate. However, when 6 is subsequently treated with CuCl, the Li-carbenoid transmetalates to Cu, which allows the controlled formation of the corresponding heterobimetallic Ir/Cu aggregate. Lastly, when Li-carbenoid 5 is treated directly with CuCl, a double transmetallation occurs from both Fe to Cu and Li-carbenoid to Cu, resulting in the trimetallic Cu cluster 8. These novel reactions pave the way for new synthetic methods to build complicated polymetallic clusters in a controlled fashion.