Host-guest interaction is one of the defining concepts of supramolecular chemistry which describes an idea of molecular recognition and interactions through non-covalent bonding between two or more molecules or ions. Based on the specific recognition of host molecules towards guest molecules, host-guest chemistry has been widely studied for drug carriers, dye encapsulation, nanoreactors, recovery of catalysts, and etc. Cyclodextrin (CD) is one of a well-known host molecule, and its hydrophobic cavity provides a strong binding interaction with azo benzenes and adamantyl group via hydrophobic attraction in water solution. We have developed a highly recoverable method for a transition metal catalyst in aqueous media via host-guest interactions using a newly designed <i>N</i>-heterocyclic carbine (NHC) ligand. The NHC ligand possesses an adamantyl tethered ethylene glycol unit for hydrophobic interaction with the cavity of β-CD. We applied this ligand to a ruthenium olefin metathesis catalyst. The catalyst provided homogeneous reactions with high performance in ring-closing metathesis, cross metathesis, and ring opening metathesis polymerization in aqueous media as well as in organic solvent. After the reaction was complete, the catalyst was removed from aqueous solution with more than 99 % efficiency by simple filtration utilizing a host-guest interaction between silica-grafted β-CD and adamantyl moiety. Due to the water soluble property of the catalyst, the catalyst was easily recovered by aqueous extraction when the reaction was run in organic solvent.

Highly efficient removal of water soluble NHC-Ru catalyst by host-guest interaction

255th National Meeting (2018)

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