Pd/Cu-catalyzed dehydrogenative coupling of dimethyl phthalate is an important industrial process for the production of aromatic polyimide precursors. Nonetheless, the detailed mechanism of the Cu cycle has remained unclear. The present study describes the detailed mechanism of the Cu cycle in the [Pd(OAc)(2)]/Cu(OAc)(2)/1,10-phenanthroline (phen) system. The solution-phase X-ray absorption fine structure analysis of the catalyst solutions and the FEFF fitting as well as the evaluation of the catalytic and stoichiometric reactions reveal the following observations: (i) the major intermediate in the catalytic cycle is a mononuclear divalent [Cu(OAc)(2)]center dot 2H(2)O species, (ii) coordination of the phen ligand to the Cu catalyst significantly inhibits the catalytic activity, (iii) 2 equiv of Cu(OAc)(2)center dot H2O oxidizes the zerovalent "Pd(phen)" species to divalent [Pd(OAc)(2) (phen)], and (iv) the divalent [Cu(OAc)(2)](2)center dot 2AcOH species is regenerated by the treatment of monovalent Cu(OAc) with AcOH in air.