Regiospecific C-H bond activation of aromatic hydrocarbons by gold(III) species and its application for cataytic reactions1

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It was found that C-H bond activation of aromatic hydrocarbons by anhydrous gold(III) chloride proceeded heterogeneously in hexane and homogeneously in diethyl ether to afford arylgold(III) complexes. As the complexes [{AuCl_2Ar}2] obtained by the above reactions are fairly unstable and gradually decomposed even in the solid state, the arylgold(III) complexes were isolated as mononuclear complexes of [AuCl_2Ar(2,6-lutidine)]. Reactions of anhydrous gold(III) chloride with aromatic hydrocarbons were investigated using nitrobenzene, acetophenone, dichlorobenzenes, chlorobenzene, benzene, toluene, xylenes, mesitylene, cumene, anisole and. As the results, it was revealed that C-H bond activation by gold(III) species proceeds electrophilically and regiospecifically. The X-ray structural analysis showed that complex [AuCl_2Ar(2,6-lutidine)] has trans configuration and both the benzene and pyridine rings stand nearly perpendicular to the co-ordination plane of gold.The reactions of arylgold(III) complexes of [AuCl_2Ar(2,6-lutidine)] with unsaturated compounds such as styrene, diphenylacetylene, dimethyl acetylenedicarboxylate, phenylacetylene, methyl propiolate and so on were investigated. It was found that alkene (styrene) as well as inner alkynes (diphenylacetylene and dimethyl acetylenedicarboxylate) did not react at all. On the contrary, a terminal alkyne phenylacetylene produced an arylated alkyne diphenylacetylene, whereas a terminal alkyne methyl propiolate yielded chlorinated methyl cinnamate derivatives ArCH = CCI(CO_2Me). Moreover, these compounds were obtained in fairly good yields by using arylgold(III) species generated in situ by the reactions of anhydrous gold(III) chloride with corresponding aromatic compounds. Concerning catalytic reactions, we could not investigate for the short period of research time.