Hiyama-Hatanaka cross coupling

The Hiyama-Hatanaka cross-coupling reaction is a more recent arylation coupling reaction that was reported by these workers in 1988 [12e, 31]. These workers demonstrated that trimethylsilylethy-lene reacts with aryl halides in the presence of a Pd(0) catalyst, a base, and a source of fluoride ion to give styrene derivatives [12e]. The source of Pd can be (it-CjHjPdCOj, Pd(Ph3P)4, or even Pdjfdbalj the base could be a hydroxide, an acetate, a phosphane, or a phosphite and the source of the fluoride ion could be tris(diethylamino)sulfonium difluoro(trimethyl)silicate (TASF), tetrabutylammonium fluoride (TBAF) or even KF (See Scheme 1.14a). The role of this reagent is shown in the catalytic cycle... 

Scheme 1.14 (a) General conditions for the Hiyama-Hatanaka cross-coupling reaction, (b) The proposed mechanism for the Hiyama-Hatanaka cross-coupling arylation procedure [31]. 

The most commonly accepted mechanism for this coupling was initially proposed by Hiyama and Hatanaka, which involves three steps.The first step is the oxidative addition of the aryl halide to the palladium(O) catalyst to give arylpalladium complex 1. The second step involves the transmetallation of the arylpalladium complex 1 with the anionic arylsilicate 2 to give bis(aryl)palladium complex 3. Finally, the cross-coupled product 4 is produced and the palladium(O) catalyst is regenerated through reductive elimination of the bis(aryl)palladium(II) complex 3. The key intermediate to this process is the requirement for the pentacoordinate arylsilicate anion 2, typically formed by treatment of the tetracoordinate silane with the activating anion, such as tetrabutylammonium fluoride (TBAF). 

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