Controlled Reversible Immobilization of Ru Carbene on Single-Walled Carbon Nanotubes: A New Strategy for Green Catalytic Systems Based on a Solvent Effect on π−π Interaction

A pyrene-tagged ruthenium carbene 8 was synthesized and immobilized on single-walled carbon nanotubes (SWNTs) via π−π stacking. These π−π interactions were greatly affected by the reaction temperature and the solvent polarity, thus, offering a new reversible immobilization model that can be controlled by reaction temperature in polar solvents, such as acetone. SWNTs-supported ruthenium carbene 8 is a robust and recyclable catalyst system. Six to seven cycles were achieved for ring-closing metathesis of selected substrates. Importantly, after the complete loss of activity, the SWNTs can be easily recycled by washing with tetrahydrofuran. The recycled SWNTs can then be reloaded with 8. The reusability of the catalyst supported on recycled SWNTs is comparable with that supported on fresh SWNTs.