Historical Perspective of the Heck Reaction

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Phosphorus-, nitrogen-, and sulfur-containing palladacycles are among the most active catalyst precursors for the promotion of such reactions reported to date. All of the palladacycles shown in this scheme promote the Heck reaction of aryl iodides with acrylic esters (Table 1). 10
All of the palladacycles shown in the Scheme promote the Heck reaction of aryl iodides with acrylic esters (Table 1). In this reaction, the highest catalytic activity observed to date was achieved with the palladacycle 6 (Table 1, Entry 9). It is interesting to note that this palladacycle only promotes the Heck reaction between aryl iodides and acrylic esters. Only a few palladacycles are active catalyst precursors for electron-rich aryl bromides (Table 1). Moreover, in the case of aryl chlorides, complexes 1, 7, 8, and 11 were found to be the only active palladacycles (Entries 24-30, Table 1). In particular, 7 promotes the Heck reaction of electron-rich aryl chlorides, such as 4- chloroanisole (Entry 29, Table 1). In contrast with the other catalyst systems presented in Table 1, the PCP-pincer complex 7 does not require the use of additives to show good activity, even with electronically, deactivated aryl chlorides. This may imply that here the active catalyst is not colloidal palladium but rather is a well defined molecular species, and currently it is not possible to rule out a Pd(II)/Pd(IV) catalytic manifold. It was proposed a catalytic cycle that proceeds via the C- H activation of the olefin at a Pd(II) centre(s) followed by oxidative addition. Complex 7 Proposed mechanism for Heck coupling catalysed by complex 7. 11
Page 1 and 2: Dimitra Kovala-Demertzi Section of
Page 3 and 4: Aryl and vinyl halides- Aryl and vi
Page 5 and 6: Solvents-Heck reactions are conduct
Page 7 and 8: Oxidative addition is often the rat
Page 9: Amino-Heck reaction In the amino-He
Page 13 and 14: The monoanionic HSal4Et ligand is c
Page 15 and 16: 3.3 Palladium nanoparticles as cata
Page 17: Figure 2. Possible pathways involve

Historical Perspective of the Heck Reaction

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