The influence of the negative neighboring group has been quantified kinetically using hydrocarbon monomers containing oxygen and sulfur. Rate constants were determined for the ADMET polymerization of bis(4-pentenyl) ether (3), bis(5-hexenyl) ether (4), bis(4-pentenyl) sulfide (5), and bis(5-hexenyl) sulfide (6) using both Schrock's catalyst Mo( CHCMe 2 Ph)( N -2,6-C 6 H 3 - i -Pr 2 )(OCMe(CF 3 ) 2 ) 2 [Mo] and Grubbs' phenyl version of the ruthenium metathesis catalyst RuCl 2 ( CHPh)(PCy 3 ) 2 [Ru] . Both catalysts experience the effect of functional group presence. Further, a pure hydrocarbon version of the negative neighboring group effect has also been demonstrated using the monomer 1,5-hexadiene. In this 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 the dissociation of phosphine ligands, thermodynamic parameters, and π complexation with the adjacent olefin in the monomer, a phenomenon similar to heteroatom nonbonded electron complexation.
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Wagener et al. (1997) studied this question.
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