Cyclopalladations, palladium® chloride

Methylphenyl)benzothiazole (80IC762) and 2-benzylbenzothiazole (95ICA(239)125) can be cyclopalladated. In the latter case, cylopalladation occurs upon reaction with palladium(II) acetate and gives the product 80. With lithium chloride, sodium bromide, or sodium iodide, a series of three products of substitution of the acetate group 81 (X = C1, Br, I) results. Pyridine, 2- and 3-methylpyridine, 2,6- and 3,5-dimethylpyridine cause the transformation of the chelate complexes 81 (X = C1, Br, I) and formation of the mononuclear products 82 (R = z= R" = = R = H, X = Cl, Br, I ... 

Milstein and co-workers were the first to introduce catalysts capable of activating various aryl chlorides in 1992 [175]. By using palladium complexes of highly basic and sterically demanding chelating bisphosphines, for example, dippb [l,4-bis(di-isopropylphosphinyl) butane], even chlorobenzene was coupled with alkenes in high yields (Table 1, 70-95% yield TON = 70-95) [175]. However, these catalysts are extremely sensitive to air. Herrmann, Beller, and co-workers introduced more robust palladacycles [cyclopalladated... 

These inserted compounds 7.23-7.25 showed unexpected thermal stability so that no reaction performed to recover the modified palladium-free ligand led to clean products. However, the stability of these compounds is very much dependent upon the nature of the other ligands on the Pd atom. Thus, changing the chloride for an iodide led to a dramatic decrease in the thermal stability of the cyclopalladated compounds [82-84]. In reactions of this latter type, the total or partial dealkylation of the NMe2 group occurs to produce compound 7.26 or compound 121, respectively, as shown in Eq. (7.24). In a related reaction, it was possible to detect the presence of Mel together with an amount of CH4 [82]. 

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