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Multivalent, Sulfur-Rich PyBox Asterisk Ligands in Asymmetric Metal Catalysis

  1. Catherine Aubert1,
  2. Carol Dallaire1,
  3. Gérard Pèpe2,
  4. E. Levillain3,
  5. Guy Félix2,
  6. Marc Gingras2

Article first published online: 20 JUL 2012

DOI: 10.1002/ejoc.201200416

Issue

European Journal of Organic Chemistry

European Journal of Organic Chemistry

Volume 2012, Issue 31, pages 6145–6154, November 2012

Additional Information

How to Cite

Aubert, C., Dallaire, C., Pèpe, G., Levillain, E., Félix, G. and Gingras, M. (2012), Multivalent, Sulfur-Rich PyBox Asterisk Ligands in Asymmetric Metal Catalysis. Eur. J. Org. Chem., 2012: 6145–6154. doi: 10.1002/ejoc.201200416

Author Information

  1. 1

    Laboratory of Supramolecular Chemistry and Catalysis, Faculty of Sciences, Université Libre de Bruxelles, 50 Ave. F. D. Roosevelt, 1050 Brussels, Belgium

  2. 2

    CNRS, UMR 7325, Aix-Marseille Univ, CINaM, 163 Ave de Luminy, 13288 Marseille, France, Fax: +33-4-91829155, http://www.cinam.univ-mrs.fr/cinam/index.php

  3. 3

    Laboratoire Moltech Anjou, UMR CNRS 6200, Université d'Angers, 2, bd. Lavoisier, 49045 Angers Cedex, France, Fax: +33-2-41735405

Publication History

  1. Issue published online: 22 OCT 2012
  2. Article first published online: 20 JUL 2012
  3. Manuscript Received: 31 MAR 2012

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Keywords:

  • Dendrimers;
  • Sulfur;
  • PyBox;
  • Assymetric catalysis;
  • Hydrosilylation

Abstract

Multivalent PyBox asterisk ligand 1 and monovalent ligand 2 are reported. The innovative feature in 1 is a sulfur-rich persulfurated benzene core as a template joining six PyBox units in close proximity. An efficient persulfuration of C6Cl6 with p-methoxybenzenethiol (95 %, >99 % per C–S bond) and deprotection led to hexaphenol 4. Six O-arylations of 4 with Cl-PyBox 3 (94 %, >99 % per C–O bond) provided 1. The electronic delocalization of 1 and 2 was analyzed by UV/Vis spectroscopy and cyclic voltammetry. PyBox ligands 1 and 2 were successfully used for Rh-catalyzed hydrosilylation of acetophenone, in spite of competitive bindings from six proximal sulfur atoms. The concept of multivalency and the presence of donating and oxidizable sulfur atoms in asymmetric metal catalysis were tested. The reactivities and the enantiocatalytic behavior of 1 and 2 with varying rhodium content were determined. Lability of the Rh complexes under certain conditions, was demonstrated by some crossover experiments with other PyBox ligands. Conformational and competitive metal binding studies of 1 with the aid of molecular modeling (GenMol™) helped to explain the results. This work suggests new directions for simple multivalent ligands in metal-mediated catalysis.

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