An unprecedented reversible inhibition/activation procedure for Grubbs-type olefin metathesis catalysts will be presented. Their metathesis activity was investigated in the presence of N-donor ligands (1-methylimidazole [MIM], 4-(N,N-dimethylamino)pyridine [DMAP], pyridine and 1-octylimidazole [OIM]). Ring Opening Metathesis Polymerization (ROMP) reactions of cyclooctene (COE), bulk-ROMP reactions of COE and norbornadiene (NBD) and Ring Closing Metathesis (RCM) reactions of diethyl diallylmalonate (DEDAM) were conducted containing various equivalents of N-donor in respect to catalyst. ROMP reactions could be entirely inhibited using MIM (1-5 equiv.) and DMAP (2-5 equiv.), and strongly inhibited with pyridine in benzene solution for 24 h. Completely inhibited ROMP reactions could be reactivated with excess phosphoric acid and the reactions proceeded faster than with uninhibited Grubbs' catalyst. ROMP reactions in neat COE and NBD could be inhibited for 72 h using 2 equiv. MIM, DMAP or OIM, and activated with phosphoric acid to give polymer gels within minutes or less. RCM reactions could be completely inhibited with MIM (1-5 equiv.), but upon activation with H3PO4 the initial activity of the uninhibited catalyst could not be restored. Detailed kinetic studies and findings on the inhibited species will be presented.
- Grubbs-type olefin metathesis catalysts,
- Ring opening metathesis polymerization,
- Ring closing metathesis,
Available at: http://works.bepress.com/hans-joerg_schanz/65/