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Ancillary Ligand and Olefin Substituent Effects on Olefin Dissociation for Cationic Zirconocene Complexes Bearing a Coordinated Pendant Olefin

Brandow, Christopher G. and Mendiratta, Arjun and Bercaw, John E. (2001) Ancillary Ligand and Olefin Substituent Effects on Olefin Dissociation for Cationic Zirconocene Complexes Bearing a Coordinated Pendant Olefin. Organometallics, 20 (20). pp. 4253-4261. ISSN 0276-7333. https://resolver.caltech.edu/CaltechAUTHORS:20170808-082527490

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Abstract

A series of zirconocene complexes bearing 2,2-dimethyl-2-sila-4-pentenyl substituents (and methyl-substituted olefin variants) ((η^5-C_5H_5)_2Zr(CH_3)(CH_2SiMe_2CH_2CR^1═CR^2R^3) (R^1, R^2, R^3 = H, CH_3, 1, 5−7), (η^5-C_5H_4CMe_3)_2Zr(CH_3)(CH_2SiMe_2CH_2CH═CH_2) (2), {Me_2Si(η^5-C_5H_4)_2}Zr(CH_3)(CH_2SiMe_2CH_2CH═CH_2) (3), and {1,2-(SiMe_2)_2(η^5-C_5H_3)_2Zr(CH_3)(CH_2SiMe_2CH_2CH═CH_2) (4)) have been prepared. Methide abstraction with B(C_6F_5)_3 results in reversible coordination of the tethered olefin to the cationic zirconium center. The kinetics of olefin dissociation have been examined using NMR methods, and the effects of ligand variation for unlinked, singly [SiMe_2]-linked, and doubly [SiMe_2]-linked bis(cyclopentadienyl) arrangements have been compared (ΔG^⧧ values for olefin dissociation vary from 11.4 to 15.6 kcal·mol^(-1) measured over the temperature range 223−283 K). For the cation derived from 4 the kinetics for olefin dissociation and site epimerization (inversion at zirconium) can be distinguished. Additionally, with this ligand system competitive binding of the olefin and the [CH_3B(C_6F_5)_3] anion is observed. Methide abstraction from {1,2-(SiMe_2)_2(η^5-C_5H_3)_2}Zr(CH_3)(CH_2CMe_2CH_2CH═CH_2) results in rapid β-allyl elimination with loss of isobutene to cleanly afford the allyl cation [{1,2-(SiMe_2)_2(η^5-C_5H_3)_2}Zr(η^3-CH_2CH═CH_2)]^+.


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http://dx.doi.org/10.1021/om010363nDOIArticle
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http://pubs.acs.org/doi/suppl/10.1021/om010363nPublisherSupporting Information
Additional Information:© 2001 American Chemical Society. Received 4 May 2001. Published online 5 September 2001. Published in print 1 October 2001. This work has been funded by the USDOE Office of Basic Energy Sciences (Grant No. DE-FG03-88ER13431). The authors thank Professor Charles Casey and Donald Carpenetti for helpful discussions of their similar results and Mr. Lawrence Henling for obtaining the X-ray crystal structure.
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Department of Energy (DOE)DE-FG03-88ER13431
Issue or Number:20
Record Number:CaltechAUTHORS:20170808-082527490
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20170808-082527490
Official Citation:Ancillary Ligand and Olefin Substituent Effects on Olefin Dissociation for Cationic Zirconocene Complexes Bearing a Coordinated Pendant Olefin Christopher G. Brandow, Arjun Mendiratta, and John E. Bercaw Organometallics 2001 20 (20), 4253-4261 DOI: 10.1021/om010363n
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:79907
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:09 Aug 2017 20:37
Last Modified:03 Oct 2019 18:25

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