What is the role of the dimeric salen ligand derived from L-tartaric acid in the asymmetric addition of trimethylsilyl cyanide to aldehydes?
Label:chem
Topic
The dimeric salen ligand derived from L-tartaric acid is synthesized by linking two salen units with 1,6-dibromohexane. This ligand is used to form a Ti complex, which acts as a catalyst for the asymmetric addition of trimethylsilyl cyanide (TMSCN) to aldehydes, producing optically active trimethylsilyl ethers of cyanohydrins.
Answer
The dimeric salen ligand plays a crucial role in enhancing the catalytic activity and enantioselectivity of the Ti complex for the asymmetric addition of TMSCN to aldehydes. The ligand's structure promotes the formation of intramolecular bimetallic Ti-salen centers, which are essential for activating the cyanide and aldehyde groups, leading to the production of chiral cyanohydrins with moderate to good enantiomeric excesses and excellent yields under relatively low catalyst loading conditions.
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