Formation of Other C-X bonds

Care must be taken in evaluating claims of activity for many metals, as traces of other metals may be the responsible catalyst Buchwald, S. L. Bohn, C. Angew. Chem., Int. Ed. 2009, 48, 5586 Bedford, R. B. Nakamura, M. et al. 

Similarly this order of reactivity is not usually observed in nucleophilic aromatic substitution reactions as loss of the leaving group is usually not the r.d.s. 

Other copper-free methods have also been reported Alami, M. Ferri, F. Linstrumelle, G. Tetrahedron Lett. 1993, 34, 6403. 

For a discussion of other metals in the Sonogashira reaction see, Plenio, H. Angew. Chem., Int. Ed. 2008,47, 6954. 

Boonsombat, J. J. Chem. Soc., Perkin Trans I IWil, 654. 

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