6533b86efe1ef96bd12cac13

RESEARCH PRODUCT

Reactivity of dialkoxydibutylstannanes toward carbon dioxide: A DFT study of electronic and steric effects

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Abstract DFT calculations were performed for the reaction of CO 2 with the monomeric species, R′ 2 Sn(OR) 2 , (R = R′ = CH 3 ; R = CH 3 , CH 2 CH 3 , CH(CH 3 ) 2 , R′ =  n -Bu) for assessing the role of electronic and steric effects in the kinetics and thermodynamics of CO 2 insertion into Sn–OR bonds. The reaction pathways are exothermic and involve the successive insertion into the two Sn–OR bonds. The driving force for insertion is ascribed to a charge-transfer between the HOMO of the complexes, mainly localized on the oxygen atom of the alkoxy ligands, and the LUMO of CO 2 . Interestingly enough, the energy barrier of the second insertion is much lower by around 27 kJ mol −1 , and quite similar whatever the alkyl and alkoxy groups studied. The thus-formed alkylcarbonato complexes undergo rotation around the Sn–O bonds which involve energy barriers sensitive to the steric hindrance of the alkyl and alkoxy groups. In the n -butyl series, the energy barriers for rotation are significantly higher than those for CO 2 insertion. As a result, the isopropylcarbonato ligand is thermodynamically and kinetically more stable toward extrusion of CO 2 , as found experimentally. The present study highlights that steric effects play a significant role on the reaction pathways for the successive insertion of CO 2 into the two Sn–O bonds. Moreover, dialkylcarbonato tin (IV) species may play a key role in the formation of dialkyl carbonate which takes place experimentally under high CO 2 pressure.