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

Abstract

Abstract Palladium(II) acetate reacts with benzene in the presence of dialkyl sulfides at 70 °C to afford novel diphenyltripalladium(II) complexes of [(R1SR2)PhPd(μ-MeCO2)2Pd(μ-MeCO2)2PdPh(R1SR2)] (1a; R1=But, R2=CH2But: 1b; R1=R2=Bui: 1c; R1=R2=Pri: 1d; R1=R2=Et). Adducts, [Pd(MeCO2)2(ButSCH2But)2] and [Pd(MeCO2)2(SPri2)2], prepared by the reactions of palladium(II) acetate and the corresponding dialkyl sulfides in benzene at 5–10 °C, change to 1a and 1c, respectively, on heating in benzene at 70 °C. In contrast, reactions of palladium(II) acetate with toluene or thiophene in the presence of 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 °C in benzene, an adduct [Pd(MeCO2)2(ButSCH2CH2Ph)2] is formed, in sharp contrast with the case of benzyl t-butyl sulfide, which gives a cyclopalladated complex under the same reaction conditions.