Ring opening metathesis polymerisations of norbornene and norbornadiene derivatives containing oxygen: a study on the regeneration of Grubbs catalyst

Abstract

Ring opening metathesis polymerisation (ROMP) of norbornene and norbornadiene derivatives containing oxygen are investigated using Grubbs well-defined ruthenium initiator. A series of 7-alkoxy norbornadiene monomers ( 2b– d ), containing alkoxy groups with decreasing steric hindrance in the 7-position have been prepared. The ROMP reactions of monomers showed that as the reaction proceeds the initiator is consumed first and then is partially regenerated at the expense of the propagating species. A small amount of another carbene species X, giving a broad signal at 17.44 ppm, is also formed which is extremely stable in solution. The species X is an active metathesis species and is able to perform ROMP on strained cyclic olefins. ROMP of monomers without alkoxy groups in the 7-position ( 3 , 4a , 4b , 5a and 5b ) and also monomers with alkoxy groups in the 5 and/or 6 positions of norbornene ( 6 and 7 ) have been performed under similar conditions. None of these systems exhibited regeneration of the initiator and no resonances due to species X can be seen in the 1H NMR spectra. The results confirm that the presence of oxygen in the 7-position of the norbornadiene monomer plays an important role in the process of regeneration of the initiator. It is found that the steric bulk and the position of substituents of the monomer have a pronounced influence on the extent of regeneration of the initiator.