Transition Metal Silylenoid Complex-Catalyzed Hydrosilation Reactions

3 Transition Metal Silylenoid Complex-Catalyzed Hydrosilation Reactions 

Cationic mthenium silylenoid complexes function as efficient hydrosilation catalysts. Tilley and Glaser reported that 1 mol% of 30 catalyzed the hydrosilation of 

1 -methylcyclohexene with phenylsilane [equation (7.5)].55 This process occurred in a diastereo- and regioselective fashion to produce silane 31 as a single isomer. Other petroleum adducts, including 1-hexene, ethene, and styrene, were efficiently hydro-silated. In addition to phenylsilane, -hexylsilane could be used without reduction of catalytic efficiency. While this reaction tolerated mono-, di-, or trisubstituted olefins, it was limited to primary silanes no reaction was observed with diethyl- or diphenylsilane, and the hydrosilation product (e.g., 31) was not converted to the tertiary silane. 

In addition to ruthenium, Tilley and coworkers also reported that cationic iridium silylenoid complexes were efficient olefin hydrosilation catalysts [reaction (7.6)].56 This silylene complex catalyzes the hydrosilation of unhindered mono- or disubsti-tuted olefins with primary silanes to produce secondary silanes with anti Markovni-kov selectivity. Iridium catalyst 32 exhibited reactivity patterns similar to those of ruthenium 30 only primary silanes were allowed as substrates. In contrast to 30, cationic iridium 32 catalyzed the redistribution of silanes. Exposing phenylsilane to 5 mol% of 32 in the absence of olefin produced diphenylsilane, phenylsilane, and silane. 

Iridium silylenoids were also reported to catalyze the hydrosilation of ketones [equation (7.7)].57 The room temperature reduction of acetophenone was achieved using only 5 mol% of silylenoid 34 to afford alkoxysilane 35 and ethyl benzene. In addition to acetophenone, acetone was also reported as a competent substrate for hydrosilation. 

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