Thermal Synthesis of Perchlorinated Oligosilanes: A Fresh Look at an Old Reaction

A combined experimental and theoretical study of the high-temperature reaction of SiCl₄ and elemental silicon is presented. The nature and reactivity of the product formed upon rapid cooling of the gaseous reaction mixture is investigated by comparison with the defined model compounds cyclo-Si₅ Cl₁₀ , n-Si₅ Cl₁₂ and n-Si₄ Cl₁₀ . A DFT assessment provides mechanistic insight into the oligosilane formation. Experimental ²⁹ Si NMR investigations, supported by quantum-chemical ²⁹ Si NMR calculations, consistently show that the reaction product is composed of discrete molecular perchlorinated oligosilanes. Low-temperature chlorination is an unexpectedly selective means for the transformation of cyclosilanes to acyclic species by endocyclic Si-Si bond cleavage, and we provide a mechanistic rationalization for this observation. In contrast to the raw material, the product obtained after low-temperature chlorination represents an efficient source of neo-Si₅ Cl₁₂ or the amine-stabilized disilene EtMe₂ N⋅SiCl₂ Si(SiCl₃ )₂ through reaction with aliphatic amines.