Catalytic hydrosilylation of olefins with organolanthanide complexes: A DFT study. Part II: Influence of the substitution on olefin and silane
Résumé
The reaction mechanism of the catalytic hydrosilylation of olefins in the presence of the samarium hydride (η5-C5H5)2SmH has been investigated for several silanes and olefins with DFT calculations. For any substrate, the active species is the silyl complex, formed in situ from the reaction of the metal hydride with the silane. In agreement with the experimental data, the substitution of hydrogen by methyl groups in the silane decreases the catalytic turn-over. This result is shown to have electronic origins: the methyl group decreases the electron density on the silicon atom, which weakens the Sm–Si bond and decreases the ability for the silyl group to stabilise the positively charged group in a σ-bond metathesis transition state. Substituting hydrogen by alkyl groups on the olefin modifies mostly steric effects, and, depending on the position of the substituting group, it can result in an increase or a decrease of the catalytic yield.