C−O and C−S Bond Cleavage in Chelating Diethers and Thioethers Promoted by η9,η5-Bis(indenyl)zirconium Sandwich Complexes:  A Combined Experimental and Computational Study

Christopher A. Bradley,† Luis F. Veiros,‡ and Paul J. Chirik*†
Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, and Centro de Quimica Estrutural, Complexo I, Instituto Superior Tcnico, Avenida Rovisco Pais 1, 1049-001 Lisbon, Portugal
Organometallics, 2007, 26 (13), pp 3191–3200
DOI: 10.1021/om0701120
Publication Date (Web): May 22, 2007
Copyright © 2007 American Chemical Society
†

 Cornell University.

,
‡

 Instituto Superior Técnico.

,
*

 Corresponding author. E-mail:  pc92@cornell.edu.

Abstract

Abstract Image

Gently warming the η6,η5-bis(indenyl)zirconium dimethoxyethane compound (η6-C9H5-1,3-(SiMe3)2)(η5-C9H5-1,3-(SiMe3)2)Zr(DME) (1-DME) to 45 °C resulted in C−O bond scission to yield an equimolar mixture of the zirconocene ethylene compound (η5-C9H5-1,3-(SiMe3)2)2Zr(η2-CH2CH2) and the corresponding zirconium bis(methoxide) complex (η5-C9H5-1,3-(SiMe3)2)2Zr(OMe)2. Monitoring the relative rates of 1-DME versus 1-DME-d10 cleavage by 1H NMR spectroscopy established no kinetic isotope effect (kH/kD = 1.0(1)), eliminating the possibility of C−H activation in or prior to the rate-determining step. Computational studies support a pathway involving rate-determining DME dissociation from the η6,η5-bis(indenyl)zirconium complex followed by facile η6 to η5 indenyl haptotropic rearrangement and C−O bond scission. Corresponding C−S bond cleavage chemistry has been investigated for three thioethers and the mechanism of bond activation compared to the oxygen congeners.

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History

  • Published In Issue June 18, 2007
  • Received February 5, 2007

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