Tris(trimethylsilyl)silane

Tris(trimethylsilyl)silane, often abbreviated as (TMS)₃SiH, is an organosilicon compound with the formula HSi[Si(CH₃)₃]₃. It is a colorless liquid and is notable as a relatively stable and readily handled source of silyl radicals.

Properties and Structure

The molecule features a central silicon atom bonded to a hydrogen atom and three trimethylsilyl (TMS) groups. The presence of the bulky TMS groups sterically protects the Si-H bond, making it less susceptible to unwanted side reactions. The silicon-hydrogen bond is relatively weak, which facilitates its homolytic cleavage to generate silyl radicals upon initiation.

Preparation

Tris(trimethylsilyl)silane can be prepared by several routes. One common method involves the reaction of tetrachlorosilane (SiCl₄) with trimethylsilyl chloride (TMSCl) in the presence of a reducing agent, such as lithium aluminum hydride (LiAlH₄) or magnesium. Other synthetic approaches also exist.

Applications

Tris(trimethylsilyl)silane is primarily used as a reagent in organic synthesis. Its key application lies in its ability to act as a reducing agent in radical chain reactions. Specifically, it can be used to:

• Reduce alkyl halides: In the presence of a radical initiator (e.g., AIBN or benzoyl peroxide), (TMS)₃SiH can abstract a halogen atom from an alkyl halide, generating an alkyl radical and a tris(trimethylsilyl)silyl radical. The alkyl radical can then abstract a hydrogen atom from another molecule of (TMS)₃SiH, regenerating the tris(trimethylsilyl)silyl radical and forming an alkane.
• Reduce selenides and tellurides: Similar to alkyl halides, (TMS)₃SiH can be used to reduce selenides and tellurides via a radical chain mechanism.
• Perform radical cyclizations: The generated alkyl radicals can also participate in intramolecular cyclization reactions before abstracting a hydrogen atom, allowing for the formation of cyclic organic molecules.
• Deoxygenation of alcohols: Via Barton-McCombie deoxygenation using xanthates or related derivatives.

Compared to tributyltin hydride (Bu₃SnH), a traditional reagent for radical reductions, (TMS)₃SiH offers several advantages:

• Lower toxicity: Tin compounds are known for their toxicity, making (TMS)₃SiH a more environmentally friendly and health-conscious alternative.
• Easier purification: The byproducts of (TMS)₃SiH reactions are typically easier to remove from the reaction mixture compared to tin-containing byproducts.

Handling and Safety

Tris(trimethylsilyl)silane is generally considered a stable compound, but it is air-sensitive and should be handled under an inert atmosphere (e.g., nitrogen or argon). It should also be protected from moisture. Appropriate personal protective equipment (PPE), such as gloves and eye protection, should be worn when handling this chemical. Consult the Material Safety Data Sheet (MSDS) for detailed safety information.