Arenediazonium salts palladium complexes

There are three areas of activity in the field of arenediazonium salts in interaction with metals and transition elements which have some similarities to metals. First is the use of copper in the reactions of Sandmeyer (1884), Pschorr (1896), Gomberg-Bachmann (1924), and Meerwein (1939). Other transition metal catalysts (Ti and Pd) have been used for such reactions since the 1970s (see Secs. 10.8 and 10.9). Up to now only one intermediate has been directly identified, the aryldiazenido palladium complex (ArN2Pd(PPh3)3]+BF4 (Yamashita et al., 1980 see Sec. 10.9, Scheme 10-64). 

The reaction between aryl or alkenyl halides or arenediazonium salts and al-kenes catalyzed by palladium complexes, the so-called Heck reaction, has been performed in aqueous media. Arylation of styrene or acryHc acid derivatives occurred in high yields in the presence of a free-ligand palladium complex as catalyst and a base (Na2C03 or K2CO3) [96-98] and, eventually, a quaternary ammonium salt [Eq. (14)] [99,100]. 

The complex [AuCl(tht)] (tht, tetrahydrothiophene) can be used instead of Cu(I) as cocatalyst in the Sonogashira reactions catalyzed by [PdCl2(PPh3)2], although this Au(I) complex is inactive in the absence of palladium [320]. Gold and palladium have also been used as catalysts in the Sonogashira reactions of arenediazonium salts [321]. 

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