Abstract
Exchange of benzylidene ligand of commercially available Grubbs catalysts 1a or 1b with an appropriate soluble-polymer supported ligand leads to new boomerang type catalysts either of the Grubbs (3) or the Hoveyda type (4a or 4b). These catalysts, supported on poly-(ethylene glycol) (PEG), were fully characterized by solution NMR and MALDI mass spectrometry. They were tested in ring-closing metathesis (RCM), and 1 H NMR analysis provided key information concerning the recovery of the catalyst at the end of the reaction. While in the case of 3 the active ruthenium did not hook back to the ligand, catalysts 4a and 4b can be recovered and recycled. 4b owning a N-heterocyclic carbene ligand is particularly active and was used in the parallel synthesis of cyclic amino esters.