Low‐Valent M( x )Al(3) Cluster Salts with Tetrahedral [SiAl(3)](+) and Trigonal‐Bipyramidal [M(2)Al(3)](2+) Cores (M=Si/Ge)

Schnöckel's [(AlCp*)(4)] and Jutzi's [SiCp*][B(C(6)F(5))(4)] (Cp*=C(5)Me(5)) are landmarks in modern main‐group chemistry with diverse applications in synthesis and catalysis. Despite the isoelectronic relationship between the AlCp* and the [SiCp*](+) fragments, their mutual reactivity is hitherto unknown. Here, we report on their reaction giving the complex salts [Cp*Si(AlCp*)(3)][WCA] ([WCA](−)=[Al(OR(F))(4)](−) and [F{Al(OR(F))(3)}(2)](−); R(F)=C(CF(3))(3)). The tetrahedral [SiAl(3)](+) core not only represents a rare example of a low‐valent silicon‐doped aluminium‐cluster, but also—due to its facile accessibility and high stability—provides a convenient preparative entry towards low‐valent Si−Al clusters in general. For example, an elusive binuclear [Si(2)(AlCp*)(5)](2+) with extremely short Al−Si bonds and a high negative partial charge at the Si atoms was structurally characterised and its bonding situation analysed by DFT. Crystals of the isostructural [Ge(2)(AlCp*)(5)](2+) dication were also obtained and represent the first mixed Al−Ge cluster.