On the Nature of the ‘Heterogeneous' Catalyst:  Nickel-on-Charcoal

Bruce H. Lipshutz,* Stefan Tasler, Will Chrisman, Bernd Spliethoff,§ and Bernd Tesche*§
Department of Chemistry & Biochemistry, University of California, Santa Barbara, California 93106-9510 and Max-Planck-Institut für Kohlenforschung, Elektronenmikroskopie, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany
J. Org. Chem., 2003, 68 (4), pp 1177–1189
DOI: 10.1021/jo020296m
Publication Date (Web): August 17, 2002
Copyright © 2003 American Chemical Society

Abstract

Abstract Image

Results from aromatic aminations and Kumada couplings, together with spectroscopic analyses (TEM, EDX, ICP-AES, React-IR), reveal that catalysis using nickel-on-charcoal (Ni/C) is most likely of a homogeneous rather than heterogeneous nature. In the course of a reaction with Ni/C, nickel bleed from the support was calculated to be as high as 78%. However, the existence of an equilibrium for this homogeneous species between nickel located inside vs outside the pore system of charcoal strongly favors the former, thus leaving only traces of metal detectable in solution. This accounts for virtually complete recovery of nickel on the charcoal following filtration of a reaction mixture and allows for recycling of the catalyst. TEM and EDX data were used to explain different reactivity profiles of Ni/C, which depended upon the method of reduction used to convert Ni(II)/C to Ni(0) as well as the level of nickel loading on the support.

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History

  • Published In Issue February 21, 2003
  • Received April 29, 2002

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