Non-metallocene ETM catalysts

Substituted cyclopentadienyl ligands are extremely effective for a variety of polymerisation reactions, but they are not unique. Both from a point of view of scientific interest and from a patent point of view, in attempts to acquire one s 

Increased steric bulk of the diimine aryl substituents leads to faster reactions This is because the ground state of the resting state is destabilised relative to the transition state and the barrier to insertion thus becomes lower. 

Another typical feature of these catalysts is the socalled chain walking . Prior to insertion of the next ethene molecule a series of P-hydride elimination and re-insertions can take place, which looks like a metal atom running along the chain. Insertion of ethene in a secondary alkyl chain leads to the formation of branches. During the isomerisation process palladium can even cross tertiary carbon atoms, since branches on branches are obtained. 

When the ethene pressure is raised the number of branches decreases, while the productivity of the catalyst remains the same (the reaction is zero order in ethene pressure). Chain walking requires an open site at the metal and obviously the competition between ethene complexation and chain walking determines the number of branches formed. 

Highly branched ethene-methyl acrylate polymers. The cationic palladium diimine complexes are remarkably tolerant towards functional groups, although the rates decrease somewhat when polar molecules are added. In ETM catalysis addition of polar molecules or monomers kills the catalyst and therefore it was very interesting to see what the new palladium catalysts would do in the presence of polar monomers. Indeed, using methyl acrylate a copolymerisation 

---