Mechanistic Insights on Pd/Cu-Catalyzed Dehydrogenative Coupling of Dimethyl Phthalate

Despite its industrial importance, very limited mechanistic information on the dehydrogenative coupling of dimethyl phthalate has been reported. Herein we report the detailed mechanism for dehydrogenative coupling of dimethyl phthalate catalyzed by [Pd­(OAc)2]/[Cu­(OAc)2]/1,10-phenanthroline·H2O (phen·H2O). The solution-phase analysis of the catalytic system by XANES shows the active species to be Pd­(II), and EXAFS supports the formation of an (acetato)­(dimethyl phthalyl)­(phen)­palladium­(II) complex from [Pd­(OAc)2]. A formation pathway of tetramethyl 3,3′,4,4′-biphenyltetracarboxylate via disproportionation of independently prepared [Pd­(OAc)­{C6H3(CO2Me)2-3,4}­(phen)] is observed with regeneration of [Pd­(OAc)2(phen)].