A Neutral Silicon(II) Half-Sandwich Compound

Area of Science:

• Organometallic Chemistry
• Main Group Chemistry
• Boron and Silicon Chemistry

Background:

• Cyclopentadienyl ligands are fundamental in organometallic chemistry.
• Low-valent silicon chemistry is an emerging field with unique reactivity.
• Borole dianions offer an alternative π-ligand system to cyclopentadienyls.

Purpose of the Study:

• To explore the metathesis reaction between a dilithio borole dianion and a silicocenium cation.
• To synthesize and characterize novel silicon(II) π-complexes.
• To investigate the reactivity and structural properties of low-valent silicon compounds.

Main Methods:

• Metathesis reaction utilizing a dilithio borole dianion and "silicocenium" cation ([Cp*Si]+).
• Synthesis and isolation of the resulting borole half-sandwich π-complex.
• Characterization using NMR spectroscopy (¹¹B and ²⁹Si) and potentially X-ray crystallography.
• Protonation experiments to induce rearrangement.

Main Results:

• Clean formation of a neutral borole half-sandwich π-complex of Si(II) and silicocene.
• The complex features an apical Si(II) atom with an accessible lone pair, enabling coordination chemistry with tungsten carbonyl.
• Protonation leads to rearrangement, forming a cationic 5-sila-6-borabicyclo[2.1.1]hex-2-ene with significant NMR spectral changes.

Conclusions:

• Demonstrated the utility of borole dianions in forming silicon(II) π-complexes.
• Reported a novel structural motif with an apical Si(II) atom and its coordination capabilities.
• Discovered a new rearrangement pathway in silicon-boron compounds upon protonation, highlighting unique reactivity.