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Platinum Metals Rev., 2004, 48, (1), 15

Palladium Perovskite Catalysts for Suzuki Couplings

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Palladium (Pd)-containing perovskites have the ability to self-regenerate under oxidative and reductive conditions, while suppressing growth of metallic Pd particles, so could be useful in automotive emissions control (1). These properties could also promote activity and long life in catalysts used in organic synthesis, where similar problems in catalyst deactivation occur.

Now researchers from the University of Cambridge, U.K., have studied Pd perovskites, such as LaFe0.57Co0.38Pd0.05O3, as catalysts for cross- coupling reactions, during Suzuki reactions of aryl halides and boronic acids (2). It was found that aryl bromides cross-coupled with boronic acids in the presence of 0.05 mol% Pd catalyst with K2CO3 as base to give the requisite biaryls in high yields (95%). Aqueous alcohols were identified as effective solvents and heating to 80°C. The catalyst was removable from the reaction mixture.

In order to study the scope and limitations of the catalyst, a reaction using 1 g of 4-methoxybromobenzene and 1 mg of (0.0038 mol% Pd) catalyst was performed. This resulted in a 93% conversion corresponding to a turnover number of 27,000.

ICP-MS showed particularly low levels of residual Pd which suggests that the catalyst may operate by a 'release and capture' mechanism, with the perovskite acting as a reservoir and scavenger for the active catalytic species. This perovskite functioned as an air-stable, reusable catalyst for Suzuki cross-coupling under mild conditions, with low levels of Pd leaching.

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References

  1.  Y. Nishihata, et al.Nature, 2002, 418, (6894), 164
  2.  M. D. Smith, A. F. Stepan, C. Ramarao, P. E. Brennan and S. V. Ley, Chem. Commun., 2003, (21), 2652

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