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Experimental and Theoretical Studies of Olefin Insertion foransa-Niobocene andansa-Tantalocene Ethylene Hydride Complexes

Ackerman, Lily J. and Green, Malcolm L. H. and Green, Jennifer C. and Bercaw, John E. (2003) Experimental and Theoretical Studies of Olefin Insertion foransa-Niobocene andansa-Tantalocene Ethylene Hydride Complexes. Organometallics, 22 (1). pp. 188-194. ISSN 0276-7333. https://resolver.caltech.edu/CaltechAUTHORS:20170310-064611489

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Abstract

Using dynamic NMR methods the rates of hydrogen exchange following intramolecular ethylene insertion into the metal−hydride bond have been measured for the following group 5 ansa-metallocene complexes:  [Me_2Si(η^5-C_5H_4)(η^5-C_5H_3-3-R)]Nb(CH_2CH_2)H (R = CHMe_2, CMe_3), rac- and meso-[Me_2Si(η^5-C_5H_3-3-CMe_3)_2]Nb(CH_2CH_2)H, and [(1,2-SiMe_2)_2(η^5-C_5H-3,5-(CHMe_2)_2)(η^5-C_5H_2-4-CMe_3)]Ta(CH_2CH_2)H. The singly bridged ansa-niobocenes exchange up to 3 orders of magnitude faster than unbridged complexes. However, the doubly bridged ansa-tantalocene complex exchanges at a rate comparable to that previously reported for (η^5-C_5Me_5)_2Ta(CH_2CH_2)H and much slower than a singly bridged complex, [Me_2Si(η^5-C_5Me_4)_2]Ta(CH_2CH_2)H. These “ansa-effects” were investigated by DFT calculations on model complexes. The computed exchange pathway showed the presence of an agostic ethyl intermediate. The calculated barriers for hydrogen exchange of model unbridged, singly bridged, and doubly bridged niobocenes correlate with the experimental results.


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http://dx.doi.org/10.1021/om0206296DOIArticle
http://pubs.acs.org/doi/full/10.1021/om0206296PublisherArticle
Additional Information:© 2003 American Chemical Society. Received 2 August 2002. Published online 7 December 2002. Published in print 1 January 2003. This work has been supported by the USDOE Office of Basic Energy Sciences (Grant No. DE-FG03-85ER13431) and Exxon Chemicals America. L.J.A. thanks the National Science Foundation for a predoctoral fellowship. We thank Dr. Nick Rees and Dr. Jeffrey Yoder for assistance with NMR experiments and Dr. Deanna Zubris for preparation of the tantalocene complex.
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Funding AgencyGrant Number
Department of Energy (DOE)DE-FG03-85ER13431
Exxon Chemicals AmericaUNSPECIFIED
NSF Predoctoral FellowshipUNSPECIFIED
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Record Number:CaltechAUTHORS:20170310-064611489
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20170310-064611489
Official Citation:Experimental and Theoretical Studies of Olefin Insertion for ansa-Niobocene and ansa-Tantalocene Ethylene Hydride Complexes Lily J. Ackerman, Malcolm L. H. Green, Jennifer C. Green, and John E. Bercaw Organometallics 2003 22 (1), 188-194 DOI: 10.1021/om0206296
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:75012
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:10 Mar 2017 15:41
Last Modified:03 Oct 2019 16:45

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