Silicon-platinum bond, cleavage

The reactions of rranj-(+)-[PtCl(SiMePh l-naphthyl )(PPhMea)2] and of its PPhg analogue with lithium aluminium hydride, triethylsilane, or thiophenol involve silicon-platinum bond cleavage. There is predominant retention of configuration at the silicon centre. A mechanism involving successive oxidative addition and reductive elimination steps, with platinum(iv) intermediates, is thought to operate for these reactions. ... 

Entries 79, 80, and 83- 86 show that the potent reducing agent LiAlH4 cleaves a variety of silicon-metal bonds, giving a hydridosilane. Nucleophilic attack by H is indicated a discussion of the associated stereochemistry is deferred until Section IV,E. When the silicon-platinum compounds shown in entries 85 and 86 are reduced, metallic platinum is formed, but the metal-containing products in other cases have not generally been identified. Equation (63) provides an example of a compound with a robust Si-Fe bond that resists reductive cleavage (237) (cf. Section III,C,3). 

Suda and coworkers described the anodic oxidation of 2-silyl-l,3-dithianes which have two sulfur atoms on the carbon adjacent to silicon [42], In this case, however, the C Si bond is not cleaved, but the C-S bonds are cleaved to give the corresponding acylsilanes (Scheme 12). Although the detailed mechanism has not been clarified as yet, the difference in the anode material seems to be responsible for the different pathway of the reaction. In fact, a platinum plate anode is used in this reaction, although a carbon anode is usually used for the oxidative cleavage of the C-Si bond. In the anodic oxidation of 2-silyl-l,3-dithianes the use of a carbon anode results in a significant decrease in the yield of acylsilanes. The effects of the nature of the solvent and the supporting electrolyte may also be important for the fate of the initially formed cation radical intermediate. Since various 2-alkyl-2-silyl-l,3-dithianes can be readily synthesized, this reaction provides a convenient route to acylsilanes. 

Although the mechanism of the platinum-catalyzed hydrosilation is poorly understood, it seems probable that an intermediate with a platinum-silicon bond is formed, with which the olefin and hydrogen may also be complexed. The cleavage of pentamethyldisilane may be rationalized by considering nucleophilic attack of isopropyl alcohol, which is used for preparing the catalyst solution, on the silicon atom that has become attached to platinum and thus vulnerable to the attack by any Lewis base (see also Section IV, A, 2,f B, 2,b). 

---