Cluster expansion and vertex substitution pathways in nickel germanide Zintl clusters

We describe the reactivity of the hypersilyl-functionalized Zintl
cluster salt K[Ge$_9$ (Hyp)$_3$] towards the nickel reagents Ni(COD)$_2$
and Ni(Cp)$_2$, which gives rise to markedly different complexes. In
the case of Ni(COD)$_2$ (COD = 1,5-cyclooctadiene), a dianionic
sandwich-like cluster [Ni{Ge9(Hyp)$_3$}$_2$]$^{2-}$ (1) was obtained, in line
with a simple ligand substitution reaction of COD by [Ge$_9$(Hyp)$_3$]$^{-}$. By
contrast, when an analogous reaction with Ni(Cp)$_2$ (Cp = cyclopenta-
dienyl) was performed, vertex substitution of the [Ge$_9$(Hyp)$_3$]$^{-}$pre-
cursor was observed, giving rise to the nine-vertex nido-cluster
(Cp)Ni[Ge$_8$(Hyp)$_3$] (2). This is the first instance of vertex substitution
at a hypersilyl-functionalized Zintl cluster cage. The electrochemical
behavior of these compounds was explored and showed reversible
redox behaviour for both clusters.