Kb. Wagener et al., KINETICS OF ACYCLIC DIENE METATHESIS (ADMET) POLYMERIZATION - INFLUENCE OF THE NEGATIVE NEIGHBORING GROUP EFFECT, Macromolecules, 30(24), 1997, pp. 7363-7369
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.