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Carboxylate-​assisted C(sp^3)​-​H activation in olefin metathesis-​relevant ruthenium complexes

Cannon, Jeffrey S. and Zou, Lufeng and Liu, Peng and Lan, Yu and O'Leary, Daniel J. and Houk, K. N. and Grubbs, Robert H. (2014) Carboxylate-​assisted C(sp^3)​-​H activation in olefin metathesis-​relevant ruthenium complexes. In: 248th American Chemical Society National Meeting & Exposition, August 10-14, 2014, San Francisco, CA.

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Ruthenium-based olefin metathesis catalysts that are selective for the synthesis of exclusively Z-olefins have advanced the utility and understanding of olefin metathesis reactions. These catalysts are synthesized with a key carboxylate-assisted C-H activation step. The study of this cyclometalation step would allow for the accelerated development of this important class of catalysts and would expand the understanding of C-H functionalization reactions in general. The mechanism of this C-H activation at metathesis-relevant ruthenium(II) benzylidene complexes was studied both exptl. and computationally. Synthesis of a ruthenium dicarboxylate at low temp. allowed for direct observation of the C-H activation step independent of initial anionic ligand exchange reactions. A first-order reaction order supports an intramol. concerted metalation-deprotonation (CMD) mechanism with ΔG‡298K = 22.2 ± 0.1 kcal×mol^(-1) for the parent N-adamantyl-N'-mesityl complex. An exptl. detd. ΔS‡ of -5.2 ± 2.6 eu supports a highly ordered transition state for carboxylate-assisted C(sp^3)-H activation. Exptl. results, including measurement of a large primary kinetic isotope effect (k_H/k_D = 8.1 ± 1.7), agree closely with a computed 6-membered carboxylate-assisted C-H activation mechanism where the deprotonating carboxylate adopts a pseudo-apical geometry, displacing the aryl ether chelate. The rate of cyclometalation was found to be influenced both by the electronics of the assisting carboxylate, and the ruthenium ligand environment.

Item Type:Conference or Workshop Item (Paper)
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URLURL TypeDescription Website
Liu, Peng0000-0002-8188-632X
Houk, K. N.0000-0002-8387-5261
Grubbs, Robert H.0000-0002-0057-7817
Alternate Title:Carboxylate-​assisted C(sp3)​-​H activation in olefin metathesis-​relevant ruthenium complexes
Additional Information:© 2014 American Chemical Society.
Record Number:CaltechAUTHORS:20140811-154233948
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48358
Deposited By: Tony Diaz
Deposited On:11 Aug 2014 23:16
Last Modified:03 Oct 2019 07:03

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