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.