Organosilicon Compounds Hiyama Coupling

An established synthetic method for arylsilanes is lithiation of aryl halides, followed by the reaction with RsSiCl. Alkenylsilanes are produced by hydrosilylation of 1-alkynes catalyzed by Rh or Pt complexes. Also aryl- and alkenylsilanes 2 are synthesized by Pd-catalyzed reaction of hexamethyldisilane with halides in the presence of TASF [78,79], 

Lee and Fu reported that coupling of phenyltrimethoxysilane (7) with alkyl bromides is possible under selected conditions. 1-Phenyldodecane was obtained in 81 % yield by the reaction of 7 with n-dodecyl bromide at room temperature. P(t-Bu)2Me as an effective ligand and BU4NF (2.4 equiv.) as an activator were used [86]. 

Some halides on silicon are activating groups. Generally two fluorine atoms are required for aryl-aryl coupling. For example, coupling of ethyl(2-thienyl)difluoro-silane (9) with 3-iodothiophene 10 afforded the bisthiophene 11 using a ligandless Pd catalyst in the presence of KF [87]. 

Electron-deficient aryl chlorides can be coupled with organo di- or trichlorosi-lanes such as aryldichloroethylsilane and aryltrichlorosilane in the presence of KF. In this case, the in situ fluorination of chlorosilanes with KF occurs. Electron-rich alkylphosphines such as tri(isopropyl)phosphine or bis(dicyclohexylphosphino)-ethane are effective ligands. For example, coupling of the dichlorosilane 12 with 4-chloroacetophenone at 120 °C in DMF gave 13 in 62% yield [88]. 

Trimethylsilanes are easily available. Coupling of commercially available trimethylvinylsilane (15) with the iodide 16 proceeds most satisfactorily using TASF and ligandless Pd in HMPA [90]. 

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Hiyama, T. Organosilicon Compounds in Cross-Coupling Reactions. In Metal Catalyzed Cross-Coupling Reactions, Diederich, F., Stang, P. J., Eds. Wiley-VCH Weinhein, 1998 Chapter 10. 

The coupling of organosilicon compounds with organic electrophiles was not disclosed until 1988 by Hatanaka and Hiyama, when they demonstrated that through the addition of an appropriate silicophilic nucleophile, those desired pentacoordinate species can be generated in situ and transfer an unsaturated group. Nucleophilic fluoride sources were found to be the additive of choice, typically TASK, TBAF, and, in some cases, KF and GsF. These are the fundamental concepts of what is nowadays called the Hiyama reaction. The use of fluoride... 

Hiyama T (1998) Organosilicon compounds in cross-coupling reactions. In de Mei-jere A, Diederich F (eds) Metal-catalyzed cross-coupling reactions. Wiley, Weinheim, p 421... 

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