Cp2Mo Catalysts for Hydrolysis, Hydrogenations and Hydrations

As for hydrogenations, predous metal catalysts have dominated the study of catalytic hydrosilylations, with Rh and Pt catalysts being prevalent in catalytic hydrosilylations. Compared to hydrogenations, however, there are more examples of cheap metals that catalyze the hydrosilylation reaction. In addition to the tungsten catalysts discussed above, several examples of iron catalysts for hydrosilylation are discussed in Chapter 4. Examples of catalytic hydrosilylations with Mn, Ti and Cu catalysts are briefly mentioned below. 

Buchwald and coworkers developed a series of titanium complexes into highly efficient catalysts for hydrosilylation of ketones. Esters were catalytically converted to alcohols by catalysts formed through reaction of Cp2TiCl2 with n-Buli, followed by reaction with HSi(OEt)3 [66]. Subsequent studies with chiral Ti catalysts led to highly enantioselective hydrosilylation of ketones [67]. 

Lipshutz and coworkers have developed copper hydride complexes with diphosphine ligands that catalyze the asymmetric hydrosilylation of aryl ketones at low temperatures (-50 to -78 °C) [68]. Nolan and coworkers discovered that copper complexes with NHC ligands are very efficient catalysts for the hydrosilylation of ketones, including hindered ketones such as di-cyclohexyl ketone and di-tert-butyl ketone [69]. 

There is a need to develop methods for P-S bond cleavage since some nerve agents used in chemical warfare are organophosphate toxins that contain P-S as well as P-O bonds. 

Hydrolysis of the P-S bond of a thiophosphinate (3.26) is catalyzed by CP2M0CI2 at temperatures as low as 20 °C [75]. A study of the hydrolysis of 0,S-diethyl phe-nylphosphonothioate, a neurotoxin mimic, catalyzed by CP2M0CI2, showed that the P-S cleavage occurred exclusively rather than P-O scission (3.27). 

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