Activation of Aromatic Carbon-Hydrogen Bonds by Palladium(II) Acetate-Dialkyl Sulfide Systems. Formation and Characterization of Novel Diphenyltripalladium(II) Complexes

Article abstract of DOI:10.1246/bcsj.62.1081

Palladium(II) acetate reacts wuth benzene in the presence of dialkyl sulfides at 70 deg C to afford novel diphenyltripalladium(II) complexes of <(R¹SR²)PhPd(μ-MeCO2)2Pd(μ-MeCO2)2PdPh(R¹SR²)> (1a; R¹=Bu^t, R²=CH2Bu^t; 1b; R¹=R²=Bu^t: 1c; R¹=R²=Prⁱ; 1d; R¹=R²=Et) Adducts, tSCH2Bu')2> and i2)2>, prepared by the reactions of palladium(II) acetate and the corresponding dilakyl sulfides in benzene at 5-10 deg C, change to 1a and 1c, respectively, on heating in benzene at 70 deg C.In contrast, reactions of palladium(II) acetate with toluene or thiophene in the presence od diisopropyl sulfide afford no isolable tolyl- or thienyl-palladium species, but coupling products, i.e. bitolyls or bithienyls, are detected by GLC analysis.Treatment of 1b with styrene produces trans-stilbene, whereas 1c reacts with carbon monoxide as well as carbon dioxide to yield benzoic acid.When palladium(II) acetate and t-butyl phenethyl sulfide are heated at 80 deg C in benzene, an adduct tSCH2CH2Ph)2> is formed, in sharp contrast with the case of benzyl t-butyl sulfide, which gives a cyclopalladated complex under the same reaction conditions.