Electronic Dissymmetry in Chiral Recognition

Seth N. Brown,* Everett T. Chu, Michael W. Hull, and Bruce C. Noll
Department of Chemistry and Biochemistry, 251 Nieuwland Science Hall, University of Notre Dame, Notre Dame, Indiana 46556-5670
J. Am. Chem. Soc., 2005, 127 (46), pp 16010–16011
DOI: 10.1021/ja055598v
Publication Date (Web): October 29, 2005
Copyright © 2005 American Chemical Society
*

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

, Seth.N.Brown.114@nd.edu

Abstract

Abstract Image

The π-bonding of the β-diketonate ligands in C2-symmetric (dike)2TiX2 complexes engenders a significant electronic dissymmetry, with the LUMO of the complex resembling a “tipped” dz2 orbital whose tilt with respect to the plane containing the metal and the two X groups is determined by the configuration at titanium. The ability of this electronic dissymmetry to promote chiral recognition has been probed in 1,1‘-bi-2-naphtholate complexes (RCOCHCOR)2Ti(BINOL) (R = CH3, Ph, or tBu). The complexes show exclusively one diastereomer by NMR, which has been established as the one predicted on electronic grounds by crystallography of the dibenzoylmethane and 2,2,6,6-tetramethylheptanedione complexes. Confirmation that the selectivity is due to electronic rather than steric factors is given by the behavior of the tin analogues, which are structurally similar but show much smaller diastereoselectivities.

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History

  • Published In Issue November 23, 2005
  • Received August 16, 2005

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