Octamethyloctahydrodibenzofluorenyl: Electronic Comparisons between a Sterically Expanded Ligand and Its Cyclopentadienyl Analogues

Craig J. Price, Paul D. Zeits, Joseph H. Reibenspies and Stephen A. Miller*†
Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255
Organometallics, 2008, 27 (15), pp 3722–3727
DOI: 10.1021/om8001526
Publication Date (Web): July 8, 2008
Copyright © 2008 American Chemical Society
* To whom correspondence should be addressed. E-mail: miller@chem.ufl.edu.
,
†

Current address: Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200.

Abstract

Abstract Image

Incorporating the octamethyloctahydrodibenzofluorenyl (Oct) ligand into metallocene and constrained geometry olefin polymerization catalysts has profound catalytic consequences. The steric influences are undoubtedly important, but it is shown herein that electronics likely also play a crucial role. The electron richness of the Oct− anion was directly measured by competitive deprotonation experiments, which reveal that the pKa of OctH is 3.9 units higher than that of fluorene. The HOMO−LUMO gap decreases by about 0.6 kcal/mol for each additional tertiary alkyl group appended to the metallocene R2C(C5H4)(C13H8)ZrCl2 (R = Me or Ph) in the 2, 3, 6, and 7 positions of the fluorenyl moiety, indicating the ability of these groups to increase the HOMO energy by electron donation. The carbonyl stretching frequencies for η5-OctMn(CO)3 (2009, 1924 cm−1) demonstrated that the Oct ligand is the most electron donating in the series of CpMn(CO)3, Cp*Mn(CO)3, and (C13H9)Mn(CO)3. DFT calculations universally corroborate these experimental findings.

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History

  • Published In Issue August 11, 2008
  • Article ASAPJuly 08, 2008
  • Received: February 19, 2008

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