Carbon monoxide tolerance electronic effect

Reaction with dimethylphenylsilane is catalyzed at room temperature under 250 psi of carbon monoxide. Other silanes tested, triethyl- and triphenylsi-lane, are not effective reagents in this system. A variety of aldehydes are good substrates for the reaction, including benzaldehyde, substituted benzaldehydes, and heterocyclic aldehydes. Aliphatic aldehydes also yield a-siloxy aldehyde products, but the reaction must be run at higher CO pressure (1000 psi) to avoid hydrosilylation. The reaction does not tolerate substrates bearing strong electron-withdrawing substituents, such as p-nitrobenzaldehyde. 

PtRu, the current choice for HOR catalysts, exhibits excellent CO tolerance, which could be ascribed to a decrease in CO binding energy on R due to electronic substrate effects and to the oxidation of chemisorbed carbon monoxide being catalyzed at low potentials by the activation of H2O [82], Ternary Pt-based catalysts have also been investigated in which a third oxophilic component such as Sn, Ir, Rh, Os, Mo, W, WO3, or Re is added to promote CO oxidation at lower potentials [83]. 

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