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DOI: 10.1055/sos-SD-221-00001

Gao, S.; Wang, D.Science of Synthesis: Metal-Catalyzed Cyclization Reactions, (2016122.

Organosilicon reagents are generally stable and less reactive toward electrophiles than other organometallic nucleophiles because of their less-polarized C—Si bonds. Active pentacoordinate silicates are reactive species in the palladium-catalyzed Hiyama coupling reaction, and are normally prepared in situ by the nucleophilic attack of a fluoride ion on silicon,[‌54‌‌60‌] as shown in Scheme 14. This active hypervalent intermediate interacts with an R1—Pd(II)—X species, formed by oxidative addition of the organic halide to palladium(0), forming a four-membered cyclic transition state 25. The key transmetalation then occurs to generate R1—Pd(II)—R2, involving the migration of a reacting organic group (R2) from silicon to the palladium(II) center. The most commonly used activators for the formation of hypervalent silicates include tris(dimethylamino)sulfonium difluorotrimethylsilane (TASF) and tetrabutylammonium fluoride (TBAF).

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