Stack by Stack: From the Free Cyclopentadienylgermanium Cation Via Heterobimetallic Main-Group Sandwiches to Main-Group Sandwich Coordination Polymers

Bis(tetrelocenes) - fusing tetrelocenes into close proximity

We report the synthesis and structure of two bis(germanocenes) and a bis(stannocene), obtained by the reaction of unsymmetric ansa bis(cyclopentadienyl) ligands with germanium and tin dichloride. DFT calculations show that the formation of these bis(tetrelocenes) is energetically favoured over the formation of the corresponding [1]tetrelocenophanes. In the crystal structure authenticated structural motif, the two tetrel(II) centers are forced into close proximity to each other, resulting in weak donor-acceptor interactions, according to Natural Bond Orbital (NBO) and Atoms in Molecules (AIM) analyses.

Low-Valent Mx Al3 Cluster Salts with Tetrahedral [SiAl3 ]+ and Trigonal-Bipyramidal [M2 Al3 ]2+ Cores (M=Si/Ge)

Schnöckel's [(AlCp*)₄ ] and Jutzi's [SiCp*][B(C₆ F₅ )₄ ] (Cp*=C₅ Me₅ ) 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(CF₃ )₃ ). The tetrahedral [SiAl₃ ]⁺ 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 [Si₂ (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 [Ge₂ (AlCp*)₅ ]²⁺ dication were also obtained and represent the first mixed Al-Ge cluster.

Cationic dialanes with fluxional π-bridged cyclopentadienyl ligands

Unique π-cyclopentadienyl bridged dialanes are synthesized as complex salts with aluminate anions by comproportionation of aluminocenium cations [Al^III(Cp)(Cp*)]⁺/[Al^IIICp₂]⁺ with [(Al^ICp*)₄]. Very short Al-Al bond lengths occur in positively charged Al₂⁴⁺ fragments. Intriguingly, the prepared asymmetric dialane shows a unique fluxional coordination of the cyclopentadienyl ligands.

Borole-based half-sandwich complexes of germanium and tin

The synthesis and initial observations regarding the reactivity of borole-based half-sandwich complexes with apical divalent group 14 elements germanium and tin are described. The 2,5-disilylborole substitution pattern allows their access via salt metathesis of the respective borole dianions.