Hetero-multimetallic Tetrakis(SCS-pincer palladium)−(Metallo)porphyrin Hybrids. Tunable Precatalysts in a Heck Reaction

Bart M. J. M. Suijkerbuijk, Sara D. Herreras Martínez, Gerard van Koten and Robertus J. M. Klein Gebbink*
Chemical Biology & Organic Chemistry, Department of Chemistry, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
Organometallics, 2008, 27 (4), pp 534–542
DOI: 10.1021/om7005613
Publication Date (Web): February 1, 2008
Copyright © 2008 American Chemical Society
* r.j.m.kleingebbink@uu.nl, Phone: +31-30-2531889 ; Fax: +31-30-2523615.

Abstract

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A series of meso-tetrakis(SCS-pincer PdCl)−(metallo)porphyrin hybrids have been synthesized using two distinct synthetic routes. Manganese and nickel were introduced into the porphyrin macrocycle prior to peripheral electrophilic palladation, whereas magnesium was introduced thereafter in light of its acid sensitivity. When these complexes were used as precatalysts in the Heck reaction between iodobenzene and styrene, different catalytic activities were observed for each hybrid complex. The catalytic activity increased for the metalloporphyrin series MnCl < 2H < Ni < Mg, which interestingly coincides with an increase of electron richness of the porphyrin ring. Control experiments on model compounds confirmed that an intramolecular effect rather than an intermolecular effect was responsible for this influence. We postulate that, in analogy with related NCN-pincer metal complexes, the electron density on the palladium atom in SCS-pincer palladium complexes is influenced by the electronic properties of the para-substituent, i.e., the metalloporphyrin in this case. This in turn influences the rate of palladium leaching and, hence, of catalysis.

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History

  • Published In Issue February 25, 2008
  • Article ASAPFebruary 01, 2008
  • Received: June 08, 2007

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