Cross-coupling reactions mechanism

Figure 2.1. Cross-coupling reactions - mechanism and name reactions...

Scheme 14. (a) Sonogashira cross-coupling reaction mechanism, (b) Click chemistry [2 + 3]... 

M. Garcia-Melchor, A. A. C. Braga, A. Lledos, G. Ujaque, F. Maseras. Computational Perspective on Pd-Catalyzed C-C Cross-Coupling Reaction Mechanisms . Acc. Chem. Res. 2013. doi 10.1021/ar400080r. 

Scheme 26 Two different mechanisms for cross-coupling reactions [9]...

The mechanism of a typical cross-coupling reaction catalyzed by Pd° or Ni° complexes can be represented by a standard catalytic cycle (Scheme 1, shown for Pd ancillary ligands not given, for simplicity). 

It proceeds by the standard mechanism for cross-coupling reactions oxidative addition of Pd(0) to the C-I bond, transmetallation to give the C-Pd(II)-C compound, and reductive elimination. 

Fig. 2 Plausible mechanism for the cross-coupling reaction of organobismuth compounds with organic halides and triflates...

Because of their frequent use, some late transition metal catalyzed carbon-carbon bond forming reactions evolved into name reactions. The most prominent examples are cross-coupling reactions, where distinction is usually made on the basis of the transmetalating agent used. The common mechanism of cross-coupling reactions and its name variants are discussed in Chapter 2.1. 

Fig. 14. Proposed mechanism for nickel-catalyzed cross-coupling reaction 66).

The formation of spirolactams 47-49 could be rationalized in terms of a sequence domino cyclization of a-allenols-cross coupling reactions. A palladium (Il)-catalyzed mechanism for the domino sequence leading to spiranic adducts 47-49 is proposed in Scheme 17. It could be presumed that the initially formed allenepalladium complex 50 undergoes an intramolecular attack by the hydroxyl group (oxypalladation), giving rise to the spirocyclic vinylic palladium species 51. 

It is assumed that the mechanism of the palladium-catalyzed cross-coupling reactions of iodonium salts involves the initial oxidative addition step, followed by ligand coupling at the iodine and then at the palladium centers analogously to the mechanism shown in Scheme 31 [63,66]. 

Reactions of alkynyliodonium salts 119 with nucleophiles proceed via an addition-elimination mechanism involving alkylidenecarbenes 120 as key intermediates. Depending on the structure of the alkynyliodonium salt, specific reaction conditions, and the nucleophile employed, this process can lead to a substituted alkyne 121 due to the carbene rearrangement, or to a cyclic product 122 via intramolecular 1,5-carbene insertion (Scheme 50). Both of these reaction pathways have been widely utilized as a synthetic tool for the formation of new C-C bonds. In addition, the transition metal mediated cross-coupling reactions of alkynyliodonium salts are increasingly used in organic synthesis. 

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