Hydrosilation of ketones

Rhodium catalyzed asymmetric hydrosilation of ketones is an excellent route to chiral alcohols in reasonable chemical yields. The reaction occurs by treatment of alkyl... 

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. 

Discrete Chiral Rhodium Phosphine Complexes as Catalysts for Asymmetric Hydrosilation of Ketones... 

To generate active, well-defined Rh catalysts for the generic hydrosilation of ketones we have synthesized a new class of Rh(I) complexes (type (b) above) which are synthesized by addition of two additional moles of Phosphine/Rh to the... 

Enantioselective Hydrosilation of Ketones and Other Carbonyl Compounds... 

Hydrosilation of Ketones. (S)-(—)-4-(2-Methylpropyl)-2-(2-pyridyl)-2-oxazoline provides a high degree of stereocontrol in the hydrosilation of acetophenone catalyzed by rhodium (eq 7). Analysis of 1-phenylethanol, isolated in 89% yield after hydrolysis, revealed 71% ee. Cationic cobalt catalysts have been used to facilitate the same transformation with this ligand generating product in 76% yield and 14% ee. ... 

The small number of examples of transition metal hydrides known to undergo addition across > C=0 is due to lack of study rather than lack of reactivity. There are numerous examples of catalytic hydrogenation and hydrosilation of ketones that involve insertions of >C=0 into M-H bonds The complex Cp2ZrH2 reacts readily with (CH3)2C = 0 to give Cp2Zr(OC3H7)2 . 

Directed and Asymmetric Reduction The principles of directed and asymmetric reactions were first developed for hydrogenation, as discussed in Section 9.2. Asymmetric hydrosilation of ketones can now be carried out cata-lytically with rhodium complexes of diop (9.22). The new chiral ligand Et-duPHOS, made by Burk at du Pont, allows chiral amination of ketones via Eq. 14.50. Note how the use of the hydrazone generates an amide carbonyl to act as a ligand, as is known to favor high e.e. (see Section 9.2). Noyori s powerful BINAP ligand has been applied to a large number of asymmetric reactions. 

Unlike the asymmetric hydrosilation of alkenes and acetylenes where Pd catalysts seem to dominate activity, for enantioselective hydrosilation of ketones a preponderance of Rh-based catalysts have been used, although a few other metals including Pd have been examined and some ligand templates such as binaphthyl are in common. 

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