Coupling reactions Grignard reagents/palladium complexes

The metal-catalyzed cross-coupling of Grignard reagents with organylhalides is mostly referred as "Kumada reaction". In most cases. Nickel catalysts have been employed, but they are not subject of this chapter. However, there are many cases based on the pioneering works of Sekiya and Ishikawa, Kumada and Hayashi, where palladium complexes are used with success " (Scheme 5-102, Scheme 5-103, Experimental Procedure below ). The POPd2 system (see also Figure 5-12) delivers... 

In a Kumada-Corriu reaction, an aryl halide is oxidatively coupled with a homogeneous nickel(ll)-phosphine catalyst [2], This species reacts with a Grignard reagent to give biaryl or alkylaryl compounds. Later, palladium-phosphine complexes were also successfully applied. By this means, stereospecific transformations were achieved. 

Unactivated aryl iodides undergo the conversion Arl — ArCHj when treated with tris(diethylamino)sulfonium difluorotrimethylsilicate and a palladium catalyst.131 A number of methods, all catalyzed by palladium complexes, have been used to prepare unsymmetrical biaryls (see also 3-16). In these methods, aryl bromides or iodides are coupled with aryl Grignard reagents,152 with arylboronic acids ArB(OH)2,153 with aryltin compounds Ar-SnR3,154 and with arylmercury compounds.155 Unsymmetrical binaphthyls were synthesized by photochemically stimulated reaction of naphthyl iodides with naphthoxide ions in an SrnI reaction.156 Grignard reagents also couple with aryl halides without a palladium catalyst, by the benzyne mechanism.157 OS VI, 916 65, 108 66, 67. 

C. Cross-coupling Reactions of Grignard Reagents in the Presence of Palladium Complexes... 

Similar to nickel catalysts, palladium complexes that have a chiral phosphine ligand enable asymmetric-coupling reactions of secondary-alkyl Grignard reagents and organic halides [246,256,257]. A study giving excellent e.e.s was selected [Eq. (173) 408] from relevant works [359,363,369]. 

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