How does the Ti-salen complex derived from the dimeric salen ligand perform in the asymmetric addition of trimethylsilyl cyanide to various aldehydes?

The Ti-salen complex, prepared from the dimeric salen ligand, is tested for its efficiency in the asymmetric addition of trimethylsilyl cyanide (TMSCN) to various aldehydes, including aromatic and aliphatic derivatives. The study evaluates the impact of different substituents on the benzene ring and the steric properties of the aldehydes on the enantioselectivity and yield of the reaction.

The Ti-salen complex derived from the dimeric salen ligand shows moderate to good catalytic activity and stereoselectivity in the asymmetric addition of TMSCN to various aldehydes. Electron-rich aromatic aldehydes generally yield higher enantioselectivities compared to electron-withdrawing substituted aldehydes. Steric congestion significantly affects the enantioselectivity, with ortho-substituted aromatic aldehydes and aliphatic aldehydes like heptaldehyde showing lower enantioselectivities. The complex provides good chemical yields for most substrates, except for trimethylacetaldehyde, which is hindered by the tert-butyl group. The study concludes that the dimeric salen ligand-based Ti complex is a practical and effective catalyst for this reaction under mild conditions.