Monomeric and dendritic second generation Grubbs- and Hoveyda–Grubbs-type catalysts for olefin metathesis

The synthesis and characterization of monomeric and dendritic Grubbs II and Hoveyda–Grubbs II-based complexes are reported. These complexes were synthesized via a route based on the connection of monomeric or dendritic N-alkyl-N′-mesitylimidazol-2-ylidene pre-ligands to Grubbs I or Hoveyda–Grubbs I complexes. The immobilization of a modified Grubbs II type catalyst on a G0 carbosilane dendrimer was successfully carried out. Together with monomeric Grubbs II and Hoveyda–Grubbs-analogs and several commercially available olefin metathesis catalysts, the soluble, homogeneous G0-dendritic Grubbs II complex was tested as catalyst in the ring closing metathesis of diethyl diallylmalonate. The immobilized complex proved to outperform its monomeric analog in this reaction at room temperature, whereas it was found to be slightly slower at reflux temperature.