Carbon-silicon bond formation catalysts

None of these difficulties arise when hydrosilylation is promoted by metal catalysts. The mechanism of the addition of silicon-hydrogen bond across carbon-carbon multiple bonds proposed by Chalk and Harrod408,409 includes two basic steps the oxidative addition of hydrosilane to the metal center and the cis insertion of the metal-bound alkene into the metal-hydrogen bond to form an alkylmetal complex (Scheme 6.7). Interaction with another alkene molecule induces the formation of the carbon-silicon bond (route a). This rate-determining reductive elimination completes the catalytic cycle. The addition proceeds with retention of configuration.410 An alternative mechanism, the insertion of alkene into the metal-silicon bond (route b), was later suggested to account for some side reactions (alkene reduction, vinyl substitution).411-414... 

Aldimines can be trifluoromethylated at the imine carbon using Me3SiCF3 in dimethyl formamide at —20 °C, using a lithium carboxylate as catalyst.71 It is proposed that the carbon-silicon bond of the reagent is activated via formation of a lithium silicate bearing carboxylate and DMF ligands on silicon. A similar process has been used for diastereoselective addition to sulftnylimims.12... 

Exhaustive cleavage of the carbon-silicon bond followed by treatment with an acid converted the complex benzo[f]furan 261 to phenol 262, as illustrated in Equation (154) <2003JA12994>. Villeneuve and Tam were able to interrupt this phenol formation by choosing Cp"Ru(COD)Cl as the catalyst. Thus, the reaction of 1,4-epoxy-1,4-dihydronaphthalene 263 with a ruthenium catalyst in 1,2-dichloroethane at 60 °C afforded the 1,2-naphthalene oxide 264 (Equation 155) <2006JA3514>. 

Three types of products have been observed in intermolecular acylations of homoallylic silanes, the major one being cyclopropylmethyl ketones, along with minor amounts of 3-butenyl ketones and -chlo-ro ketones. It is likely that all derive from the carbenium ion formed by acylation of the double bond, which then undergoes cyclodesilylation or hydride transfer followed by 3-elimination (Scheme 14). The former leads to the cyclopropane, which can ring open to give the chloro products. The latter pathway gives the butenyl ketone, and is supported by location of substituent positions on methylated substrates. However, the direct acylation of the carbon-silicon bond should not necessarily be excluded in consideration of more general cases. Titanium tetrachloride seems the preferred catalyst in these cyclodesilyl-ations, and low temperatures minimize the formation of the chloro by-products. Intramolecular versions... 

Several observations led to the proposal that some of the catalysts containing metals other than platinum do not react by the Chalk-Harrod mechanism. First, carbon-silicon bond-forming reductive elimination occurs with a sufficiently small number of complexes to suggest that formation of the C-Si bond by insertion of olefin into the metal-silicon bond could be faster than formation of the C-Si by reductive elimination. Second, the formation of vinylsilane as side products - or as the major products in some reactions of silanes with alkenes cannot be explained by the Chalk-Harrod mechanism. Instead, insertion of olefin into the M-Si bond, followed by p-hydrogen elimination from the resulting p-silylalkyl complex, would lead to vinylsilane products. This sequence is shown in Equation 16.39. Third, computational studies have indicated that the barrier for insertion of ethylene into the Rh-Si bond of the intermediate generated from a model of Wilkinson s catalyst is much lower than the barrier for reductive elimination to form a C-Si bond from the alkylrhodium-silyl complex. ... 

Transition-metal catalyzed cross-coupling reactions have been demonstrated to be an extremely powerful tool for the construction of carbon-carbon bonds in regio- and stereoselective manners. These metal catalysts enable the transmetallation of carbon-silicon bonds into other carbon-metal bonds from which further reactions can proceed, leading to carbon-carbon bond formation. The use of palladium catalyst in the activation of the carbon-silicon bond is particularly noteworthy various important transformations have thus been developed. The presence of fluoride ions will make the reaction more facile, pentacoordinate organofluorosiUcates being presumably formed under these conditions . ... 

ZnBr2 also work as an effective catalyst for the carbonyl insertion into 187b (Scheme 10.253) [684]. The Zn-catalyzed system is valuable for insertion of aldehydes and ketones (including aliphatic compounds) as well as formates. In sharp contrast to the Cu-catalyzed reaction, the zinc-catalyzed reaction inserts these carbonyl compounds into the less substituted silicon-carbon bond of 187b with high... 

The hydrosilylation reaction (16,17) is a well known reaction for formation of silicon carbon bonds. When vinyl-containing polysiloxane is reacted with multi-Si-H-containing polysiloxane in the presence of a platinum catalyst, a crosslinked network forms, equation 10. Platinum is so active for the hydrosilylation reaction that inhibitors are added to moderate the rate of crosslinking (18). A typical platinum catalyst used by industry is the so-called Karstedt catalyst (19,20). A reaction of Karstedt s catalyst with a ligand, L (an inhibitor perhaps), is shown in equation 11. 

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