Bimetallic Cu/Pd(ppm)-catalyzed Suzuki-Miyaura couplings: DFT studies on mechanism, roles of Pd(ppm) and ligands

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Transition metal-catalyzed Suzuki-Miyaura coupling (SMC) reaction is an important method to constructe the C-C bond. In this work, the mechanisms of SMC between ArI and ArB(OH)2 (Ar=C6H4(OCH3)) catalyzed by single [Cu] catalyst and bimetallic [Cu]/[Pd] catalysts have been studied by DFT calculations. Comparing to the N, O-bidentate ligand, the N, P-bidentate ligand coordinated [L12-Cu] catalyst is not efficient for the above reaction, due to the high energy barrier of the C-C coupling procedure. The different coordination mode of the N, O-bidentate ligand increases the positive charge of coupling C atom, lowering the energy barrier when catalyzed by [L13-Cu]. The [Cu]/[Pd] catalyzed process involves two cycles: LCuAr is obtained from the [Cu] catalyzed cycle by the reaction between ArB(OH)2 and [L12Cu]. The [Pd] catalyzed cycle consists of four steps: L12Pd(0) insertion into C-I bond by oxidation addition, coordination transformation, transmetallation between LCuAr and ArPdI, and C-C coupling by reductive elimination. In these two cycles, the coordination transformation of the Pd is the rate-determining step. The participation of [Pd] catalyst changes the C-C coupling process from the Cu center to the Pd center, which lowers the energy barrier and makes the reaction become easier.