Olefin metathesis catalysts (H 2 ITap)(PCy 3 )Cl 2 Ru=CHPh ( 4 ) and (H 2 ITap)Cl 2 Ru=CH‐(C 6 H 4 ‐O‐ i Pr) ( 5 ) [H 2 ITap = 1,3‐bis(2′,6′‐dimethyl‐4′‐dimethylaminophenyl)‐4,5‐dihydroimidazol‐2‐ylidene] were used for the ring‐opening metathesis polymerization (ROMP) of exo ‐7‐oxanorbornene derivative 7 in the presence of various amounts of acid. Upon gradual protonation of the NMe 2 groups of the H 2 Tap ligand, the metathesis activity of both catalysts were gradually reduced due to electronic changes of the N‐heterocyclic carbene (NHC) ligand donor capability. The investigation of the ROMP polymer 8 , DFT calculations and measurements of the initiation kinetics prove that the reduced activity is solely due to reduced rates of propagation.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
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Balof et al. (2009) studied this question.
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