Pd/Cu-Catalyzed Dehydrogenative Coupling of Dimethyl Phthalate: Synchrotron Radiation Sheds Light on the Cu Cycle Mechanism

Abstract

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 ]•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 •H 2 O oxidizes the zerovalent "Pd(phen)" species to divalent [Pd(OAc) 2 (phen)], and (iv) the divalent [Cu(OAc) 2 ] 2 •2AcOH species is regenerated by the treatment of monovalent Cu(OAc) with AcOH in air.

Mechanistic Investigation into the Regio-Controllable Hydroallylations of Alkynes with Allylborons under Pd-Based Synergetic Catalyses

“…In this subsection, based on the theoretical calculations, we tentatively established a Cu­(OAc) 2 -assisted (Ac)­O-H activation/alkyne insertion mechanism in Figure , which has been rarely reported in previous Pd/Cu-catalyzed documents . In the newly proposed mechanism (black line), the AcOH combination with Md first gives adduct IM12 with a small energy increase of 2.2 kcal/mol, which follows the (Ac)­O-H cleavage via TS12–13 and generates IM13 .…”

Theoretical Exploration of Rh/Cu Cooperative Catalysis in C–H Allylation of Benzamide with 1,3-Diene

“…The translational entropy of the DMA molecule in solution is 16.9 cal mol –1 K –1 , corresponding to the free energy change of −5.8 kcal mol –1 due to the entropy contribution at the temperature of 343 K. Consequently, in a DMA solution, cupric acetate can exist in the state of Cu(OAc) 2 ·DMA, similar in structure to Cu(OAc) 2 ·H 2 O. In an aqueous solution, cupric acetate can exist as Cu(OAc) 2 ·2H 2 O, and a similar structure has been identified in DMA solution. The free energy change for the reaction involving 1 2 false[ C u false( normalO normalA normalc false) 2 false] 2 + 2DMA → Cu(OAc) 2 ·2DMA is −4.0 kcal mol –1 , as this reaction can also be approximated as a pseudo first-order reaction.…”

Synergic Palladium Catalysis for Aerobic Oxidative Coupling

“…More recently, Mitsudome, Takaya, Hirano and co‐worker reported a detailed mechanism for the Pd/Cu‐catalyzed dehydrogenative coupling of dimethyl phthalate based on solution‐phase XAFS analysis. This work demonstrated the role of a Cu salt in this reaction, which functioned not as a heteronuclear species with a direct Pd−Cu bond but rather as a catalyst re‐oxidant [72] …”

“…This work demonstrated the role of a Cu salt in this reaction, which functioned not as a heteronuclear species with a direct PdÀ Cu bond but rather as a catalyst reoxidant. [72] A stoichiometric reaction in which a [Pd(dba)(phen)] complex reacts with two equivalents of Cu(OAc) 2 • H 2 O under an inert atmosphere has been shown to generate a divalent palladium species. This prior work indicated the role of Cu(II) as a catalyst in the dehydrogenative coupling based on the reoxidation of palladium(0) species (Scheme 6a).…”