Controlled cluster expansion at a Zintl cluster surface

Reaction of the tris-hypersilyl nonagermanide Zintl cluster salt, K[Ge$_9$(Hyp)$_3$] (Hyp=Si(SiMe$_3$)$_3$) with [Rh(η$^2$,η$^2$-L)Cl]$_2$ (L=1,5-cyclooctadiene, COD; norbornadiene, NBD) afforded eleven- and twelve-vertex homo-multimetallic clusters by cluster core expansion. Using a stepwise procedure, starting from the Zintl cluster [Rh(COD){Ge$_9$(Hyp)$_3$}] and [Ir(COD)Cl]$_2$, this methodology was expanded for the synthesis of eleven-vertex hetero-multimetallic clusters. A mechanism for the formation of these first examples of closo eleven-vertex Zintl clusters is proposed, informed by density functional theory calculations.