Cyclodextrin Cavity-Induced Mechanistic Switch in Copper-Catalyzed Hydroboration

Area of Science:

• Organometallic Chemistry
• Supramolecular Chemistry
• Catalysis

Background:

• N-heterocyclic carbenes (NHCs) are versatile ligands in catalysis.
• Cyclodextrins (CDs) are known for their host-guest chemistry and ability to modify ligand properties.
• Combining NHCs with CDs creates novel ligand architectures with tunable properties.

Purpose of the Study:

• To investigate the regioselectivity of copper-catalyzed hydroboration using N-heterocyclic carbene-capped cyclodextrin (ICyD) ligands.
• To elucidate the mechanistic pathways governing the observed regioselectivity.
• To explore the influence of cyclodextrin cavity size on catalytic outcomes.

Main Methods:

• Synthesis of α-ICyD and β-ICyD ligands derived from α- and β-cyclodextrins.
• Copper-catalyzed hydroboration reactions.
• Mechanistic studies to differentiate reaction pathways.

Main Results:

• α-ICyD and β-ICyD ligands exhibited opposite regioselectivities in copper-catalyzed hydroboration.
• The observed regioselectivity switch was attributed to two distinct mechanisms: a conventional parallel pathway and a novel orthogonal pathway.
• The cavity shape of the cyclodextrin core was identified as the key factor inducing both the regioselectivity and mechanistic switch.

Conclusions:

• The study demonstrates that the cavity dimensions of ICyD ligands can control both regioselectivity and reaction mechanisms in copper catalysis.
• This work expands the understanding of host-guest interactions in catalysis and broadens the scope for designing selective catalysts.
• ICyD ligands represent a promising platform for fine-tuning catalytic performance through supramolecular control.