Naphthoquinone palladium complexes

A series of palladium(O) mono-imidazolylidene complexes have also been prepared and used for the Heck reaction of aryl chlorides in [NBu4]Br.29 The authors report that two of their catalysts, (1,3-dimesi-tylimidazolylidene)(naphthoquinone)palladium(0) and (1,3-dimesitylimida-zolylidene)(benzoquinone)palladium(0) (Fig. 5) remain stable throughout the reaction and will couple even non-activated aryl chlorides in good yields. Clearly, the authors believe that the imidazolylidene complex is responsible for this activity. 

An improved method for the synthesis of hydrogen peroxide from carbon monoxide, water and oxygen catalyzed by palladium complexes in presence of a quinone co-catalyst is described. The use of 1,4-naphthoquinone and 1,10-phenanthroline as palladium ligand resulted in a marked catalyst stabilization against deactivation processes such as polynuclear species formation and Pd-black precipitation, which are very fast operating in the absence of quinone. 

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