Siemens Reloaded: Chloride-Assisted Selective Hydrodechlorination of SiCl to HSiCl.

Trichlorosilane is the key intermediate for the large-scale production of polycrystalline silicon in the Siemens and Union Carbide processes. Both processes, however, are highly inefficient, and over two thirds of the trichlorosilane employed is converted to unwanted silicon tetrachloride accumulating in millions of tons per year on a global scale. In this combined experimental and theoretical study we report an energetically and environmentally benign synthetic protocol for the highly selective conversion of SiCl to HSiCl using organohydridosilanes as recyclable hydrogen transfer reagents in combination with onium chlorides as efficient catalysts.

Disilane Cleavage with Selected Alkali and Alkaline Earth Metal Salts.

The industry-scale production of methylchloromonosilanes in the Müller-Rochow Direct Process is accompanied by the formation of a residue, the direct process residue (DPR), comprised of disilanes Me Si Cl (n=1-6). Great research efforts have been devoted to the recycling of these disilanes into monosilanes to allow reintroduction into the siloxane production chain. In this work, disilane cleavage by using alkali and alkaline earth metal salts is reported.

Making Use of the Direct Process Residue: Synthesis of Bifunctional Monosilanes.

The industrial production of monosilanes Me SiCl (n=1-3) through the Müller-Rochow Direct Process generates disilanes Me Si Cl (n=2-6) as unwanted byproducts ("Direct Process Residue", DPR) by the thousands of tons annually, large quantities of which are usually disposed of by incineration. Herein we report a surprisingly facile and highly effective protocol for conversion of the DPR: hydrogenation with complex metal hydrides followed by Si-Si bond cleavage with HCl/ether solutions gives (mostly bifunctional) monosilanes in excellent yields. Competing side reactions are efficiently suppressed by the appropriate choice of reaction conditions.

Lewis Base Catalyzed Selective Chlorination of Monosilanes.

A preparatively facile, highly selective synthesis of bifunctional monosilanes R SiHCl, RSiHCl and RSiH Cl is reported. By chlorination of R SiH and RSiH with concentrated HCl/ether solutions, the stepwise introduction of Si-Cl bonds is readily controlled by temperature and reaction time for a broad range of substrates. In a combined experimental and computational study, we establish a new mode of Si-H bond activation assisted by Lewis bases such as ethers, amines, phosphines, and chloride ions.

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

A combined experimental and theoretical study of the high-temperature reaction of SiCl 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-Si Cl , n-Si Cl and n-Si Cl . A DFT assessment provides mechanistic insight into the oligosilane formation.