ACTIVATION OF AROMATIC CARBON HYDROGEN-BONDS OF METHYL-SUBSTITUTED BENZENES BY THE PALLADIUM(II)ACETATE-DIISOBUTYL SULFIDE SYSTEM

Aromatic C-H bond activation of various methyl-substituted benzenes by the Pd(MeCO2)2-SBu2i system have been studied. In the case of p-xylene the new and unusual compound [(SBu2i)(2,5-Me2C6H3)Pd(mu-MeCO2)2Pd(mu-MeCO2)2Pd(2,5-Me2C6H3)(SBu2i)] (1) has been isolated. Complex 1 reacts with styrene and carbon monoxide to afford (E)-1-(2,5-dimethylphenyl)-2-phenylethene and 2,5-dimethylbenzene carboxylic acid, respectively. It has also been found that coupling products, biaryls, are formed in the reaction between Pd(MeCO2)2-SBu2i and methyl-substituted benzenes. The isolated aryl-palladium(II) complexes and the coupling products have been characterized and identified by means of H-1 NMR, GC-MS, and elemental analysis. On the basis of the isomer distribution of both isolated arylpalladium(II) complexes and the coupling products, the effect of the methyl groups on the benzene nucleus towards aromatic C-H bond activation is discussed.