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Dimeric n-Alkyl Complexes of Rare-Earth Metals Supported by a Linked Amido−Cyclopentadienyl Ligand: Evidence for β-Agostic Bonding in Bridging n-Alkyl Ligands and Its Role in Styrene Polymerization

Voth, Peter and Arndt, Stefan and Spaniol, Thomas P. and Okuda, Jun and Ackerman, Lily J. and Green, Malcolm L. H. (2003) Dimeric n-Alkyl Complexes of Rare-Earth Metals Supported by a Linked Amido−Cyclopentadienyl Ligand: Evidence for β-Agostic Bonding in Bridging n-Alkyl Ligands and Its Role in Styrene Polymerization. Organometallics, 22 (1). pp. 65-76. ISSN 0276-7333. https://resolver.caltech.edu/CaltechAUTHORS:20170310-070935010

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Abstract

The dimeric rare-earth hydrides [Ln(η^5:η^1-C_5Me_4SiMe_2NCMe_3)(THF)(μ-H)]_2 (Ln = Y, Yb) react with excess α-olefin H_2C ═ CHR (R = Et, ^nPr, ^nBu) in a 1,2-insertion to give the series of THF-free dimeric n-alkyl complexes [Ln(η^5:η^1-C_5Me_4SiMe_2NCMe_3)(μ-CH_2CH_2R)]_2 as isolable crystals. Single-crystal X-ray diffraction studies on the five derivatives [Y(η^5:η^1-C_5Me_4SiMe_2NCMe_2R‘)(μ-CH_2CH_2R)]_2 (R‘ = Me, R = Et, ^nBu; R‘ = Et, R = Et, ^nPr) and [Yb(η^5:η^1-C_5Me_4SiMe_2NCMe_3)(μ-CH_2CH_2^nBu)]_2 revealed that the centrosymmetric dimeric complexes consist of two trans-arranged [Ln(η^5:η^1-C_5Me_4SiMe_2NCMe_2R‘)] fragments connected by two μ-alkyl ligands. Most strikingly, there is an agostic interaction of the n-alkyl groups' β-CH_2 hydrogen atoms with the formally 12-electron lanthanide metal center. Variable-temperature NMR spectroscopic data suggest a fluxional process that interconverts the diastereotopic protons of the α-CH_2 group and a dynamic β-agostic interaction. Addition of >10 equiv of THF per yttrium to a solution of [Y(η^5:η^1-C_5Me_4SiMe_2NCMe_3)(μ-CH_2CH_2Et)]_2 results in the formation of the highly reactive, nonisolable, monomeric THF adduct [Y(η^5:η^1-C_5Me_4SiMe_2NCMe_3)(CH_2CH_2Et)(THF)]. Reaction of 1,2-dimethoxyethane (DME) with [Y(η^5:η^1-C_5Me_4SiMe_2NCMe_3)(μ-CH_2CH_2Et)]_2 forms the crystalline compound [Y(η^5:η^1-C_5Me_4SiMe_2NCMe_3)(CH_2CH_2Et)(DME)] with a terminal n-butyl group that contains a slightly distorted α-carbon atom according to a crystallographic study. α-Olefins having two or more substituents on the γ-carbon do not react with the hydride complexes. The role of these n-alkyl complexes in the controlled polymerization of styrene is discussed.


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http://dx.doi.org/10.1021/om0206599DOIArticle
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http://pubs.acs.org/doi/suppl/10.1021/om0206599PublisherSupporting Information
Additional Information:© 2003 American Chemical Society. Received 13 August 2002. Published online 2 December 2002. Published in print 1 January 2003. Generous financial support by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie is gratefully acknowledged. We thank Dr. B. Mathiasch and Dr. N. Rees for obtaining various NMR spectroscopic data and S. Hennig for collecting the diffraction data of 2a and 9a.
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Deutsche Forschungsgemeinschaft (DFG)UNSPECIFIED
Fonds der Chemischen IndustrieUNSPECIFIED
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Official Citation:Dimeric n-Alkyl Complexes of Rare-Earth Metals Supported by a Linked Amido−Cyclopentadienyl Ligand:  Evidence for β-Agostic Bonding in Bridging n-Alkyl Ligands and Its Role in Styrene Polymerization Peter Voth, Stefan Arndt, Thomas P. Spaniol, Jun Okuda, Lily J. Ackerman, and Malcolm L. H. Green Organometallics 2003 22 (1), 65-76 DOI: 10.1021/om0206599
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:75013
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:10 Mar 2017 15:39
Last Modified:03 Oct 2019 16:45

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