Issue 5, 2010

Ni-, Pd-, or Pt-catalyzed ethylenedimerization: a mechanistic description of the catalytic cycle and the active species

Abstract

Two key mechanistic possibilities for group 10 transition metal [M(η3-allyl)(PMe3)]+ catalyzed (where M = Ni(II), Pd(II) and Pt(II)) ethylene dimerization are investigated using density functional theory methods. The nature of the potential active catalysts in these pathways is analyzed to gain improved insights into the mechanism of ethylene dimerization to butene. The catalytic cycle is identified as involving typical elementary steps in transition metal-catalyzed C–C bond formation reactions, such as oxidative insertion as well as β-H elimination. The computed kinetic and thermodynamic features indicate that a commonly proposed metal hydride species (LnM–H) is less likely to act as the active species as compared to a metal–ethyl species (LnM–CH2CH3). Of the two key pathways considered, the active species is predicted to be a metal hydride in pathway-1, whereas a metal alkyl complex serves as the active catalyst in pathway-2. A metal-mediated hydride shift from a growing metal alkyl chain to the ethylene molecule, bound to the metal in an η2 fashion, is predicted to be the preferred route for the generation of the active species. Among the intermediates involved in the catalytic cycle, metal alkyls with a bound olefin are identified as thermodynamically stable for all three metal ions. In general, the Ni-catalyzed pathways are found to be energetically more favorable than those associated with Pd and Pt catalysts.

Graphical abstract: Ni-, Pd-, or Pt-catalyzed ethylene dimerization: a mechanistic description of the catalytic cycle and the active species

Supplementary files

Article information

Article type
Paper
Submitted
14 Oct 2009
Accepted
20 Nov 2009
First published
11 Jan 2010

Org. Biomol. Chem., 2010,8, 1040-1051

Ni-, Pd-, or Pt-catalyzed ethylene dimerization: a mechanistic description of the catalytic cycle and the active species

D. Roy and R. B. Sunoj, Org. Biomol. Chem., 2010, 8, 1040 DOI: 10.1039/B921492E

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