Catalytic Reactions

Abstract

The second type of reactions involving palladium compounds are catalytic reactions. Reactions of this type proceed by the use of a catalytic amount of palladium compounds sometimes with certain ligands, but without reoxidants. Often Pd(PPh₃)₄ is used, but more conveniently, PdCl₂ or Pd(OAc)₂ is used with PPh₃ as catalyst. In many cases, these Pd²⁺ species are reduced in situ to a Pd⁰ state, which behaves as a true catalyst. Ligands such as PPh₃ seem to stabilize a low valent state of palladium. Sometimes metallic palladium is used as a catalyst. Different palladium species show different catalytic activity. Proper selection of palladium species and ligands is essential for attaining maximum activity. Since only a tiny amount of palladium is required, the catalytic reactions are more useful than the stoichiometric reactions described in Chap. III. In the following, various catalytic reactions are classified and surveyed. The well established palladium-catalyzed simple hydrogenation of olefins is not treated. Also the palladium catalyzed double bond migration reaction from terminal to internal positions is omitted with few exceptions.