hydrosilylation

Hydrosilylation is the chemical reaction in which a silicon–hydrogen bond (Si–H) adds across a multiple bond, most commonly a carbon–carbon double or triple bond. The process forms a new carbon–silicon bond and an alkyl or vinyl silane. It is widely used to prepare organosilicon compounds under relatively mild conditions and with broad functional‑group tolerance.

Catalysis and scope

Most hydrosilylation reactions are catalyzed by transition metal complexes, including platinum, rhodium, palladium, ruthenium, and nickel. A classic and widely used example is Karstedt’s platinum catalyst. The reaction is versatile and can be applied to alkenes, internal and terminal alkenes, and alkynes to furnish vinylsilanes or alkylsilanes. Regio- and stereoselectivity depend on the substrate and the catalyst system; many systems favor anti-Markovnikov addition of Si–H to terminal alkenes, but outcomes vary with ligands and metal centers. Chiral ligands enable enantioselective variants for prochiral substrates.

Mechanism

Although details vary with the catalyst, a common framework involves activation of the Si–H bond by the metal to form M–H and M–Si species, followed by migratory insertion of the C=C or C≡C bond into the M–Si (or M–H) fragment and subsequent reductive elimination to release the C–Si bond product and regenerate the catalyst. Several mechanistic pathways exist, but coordination chemistry and oxidative addition–insertion steps underpin most catalytic cycles.

Applications

Hydrosilylation provides a straightforward route to organosilanes, vinyl silanes, and alkyl silanes used in organic synthesis, protecting group strategies, surface modification, and the curing or crosslinking of silicone polymers through Si–H adding to vinyl or allyl groups.