KINETICS OF ACYCLIC DIENE METATHESIS (ADMET) POLYMERIZATION - INFLUENCE OF THE NEGATIVE NEIGHBORING GROUP EFFECT

The influence of the negative neighboring group has been quantified ki netically using hydrocarbon monomers containing oxygen and sulfur. Rat e constants were determined for the ADMET polymerization of bis(4-pent enyl) ether (3), bis(5-hexenyl) ether (4), bis(4-pentenyl) sulfide (5) , and bis(5-hexenyl) sulfide (6) using both Schrock's catalyst Mo(=CHC Me2Ph)(N-2,6-C6H3-i-Pr-2)(OCMe(CF3)(2))(2) [Mo] and Grubbs' phenyl ver sion of the ruthenium metathesis catalyst RuCl2(=CKPh)(PCy3)(2) [Ru]. Both catalysts experience the effect of functional group presence. Fur ther, a pure hydrocarbon version of the negative neighboring group eff ect has also been demonstrated using the monomer 1,5-hexadiene. In thi s case, [Mo] catalysis produces linear 1,4-polybutadiene in a reaction that exhibits a typical ADMET rate constant and activation energy. On the other hand, [Ru] catalysis leads principally to the formation of cyclic compounds rather than linear polymers. This change in mechanism for [Ru] catalysis can be attributed to multiple factors including th e dissociation of phosphine ligands, thermodynamic parameters, and pi complexation with the adjacent olefin in the monomer, a phenomenon sim ilar to heteroatom nonbonded electron complexation.