The organocatalytic activity of the recently synthesized diaminoferrocenophanes and the related thioaminoferrocenophane was investigated in the benzoin condensation computationally. The nucleophilicity of these compounds is slightly increased compared to the imidazolidin-2-ylidene, as a consequence of the increased bond angle at the carbene center. Among the possible isomers of the carbene–aldehyde adducts, we have located a hitherto unexplored structure with an oxirane moiety. The isomers of the related carbene–aldehyde adducts including the Breslow intermediates have similar stability in comparison with the imidazolidin-2-ylidene and thiazolidin-2-ylidene, respectively; moreover, the barriers of the interconversion of these adducts are also similar; however, the oxirane-type compound formed from benzaldehyde and the diaminoferrocenophane is significantly stabilized with respect to its isomers. The barrier of the addition of the second aldehyde to the Breslow intermediate increased by 9–15 kcal/mol in case of the ferrocenophanes compared to the 5-membered analogues, which could partly be explained by the higher stabilization of the van der Waals adduct of the Breslow intermediate and the second aldehyde. Since the addition of the second aldehyde is blocked, these carbenes could be suitable for the experimental investigation of the carbene–aldehyde adducts.
- Benzoin condensation
ASJC Scopus subject areas
- Condensed Matter Physics
- Physical and Theoretical Chemistry