Ru-based olefin metathesis catalysts bearing ph-responsive n-heterocyclic carbene (NHC) ligands: Activity control via degree of protonation

Balof, S. and Yu, B. and Lowe, A. and Ling, Y. and Zhang, Y. and Schanz, H. 2009. Ru-based olefin metathesis catalysts bearing ph-responsive n-heterocyclic carbene (NHC) ligands: Activity control via degree of protonation. European Journal of Inorganic Chemistry (13 SPEC. ISS.): pp. 1717-1722.

Source Title

European Journal of Inorganic Chemistry

DOI

10.1002/ejic.200801145

ISSN

1434-1948

School

Nanochemistry Research Institute

URI

http://hdl.handle.net/20.500.11937/5682

Collection

Curtin Research Publications

Abstract

Olefin metathesis catalysts (H2ITap)(PCy3)Cl2Ru=CHPh (4)and (H2ITap)Cl2Ru=CH-(C6H4-O-iPr) (5)[H2ITap = 1,3-bis-(2-,6-dimethyl-4- dimethylaminophenyl)-4,5-dihydroimid-azol-2-ylidene] were used for the ring-opening metathesispolymerization (ROMP) of exo-7-oxanorbornene derivative 7in the presence of various amounts of acid. Upon gradualprotonation of the NMe2 groups of the H2Tap ligand, the me-tathesis activity of both catalysts were gradually reduced dueto electronic changes of the N-heterocyclic carbene (NHC)ligand donor capability. The investigation of the ROMP poly-mer 8, DFT calculations and measurements of the initiationkinetics prove that the reduced activity is solely due to re-duced rates of propagation. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009.