Modified N-Heterocyclic Carbene Ligand for the Recovery of Olefin Metathesis Catalysts via Noncovalent Host-Guest Interactions

A general method, focusing upon olefin metathesis, was developed for the recovery of homogeneous olefin metathesis catalysts from crude reaction solutions. This method utilizes the supramolecular host-guest interaction between an azobenzene-modified N-heterocyclic carbene ligand and a silica-grafted beta-cyclodextrin to remove homogeneous catalyst in a heterogeneous manner, allowing for the recovery of more than 97% of ruthenium in solution. The robust and simple nature of the guest molecule allows for the application of this method to a wide range of homogeneous catalysts. This study reports the synthesis and characterization of the said precatalyst and host compound as well as proof-of-concept recovery trials for a number of common substrates, with the residual ruthenium content of reaction mixtures evaluated by inductively coupled plasma mass spectrometry.