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DFT calculations have been used to explore the full catalytic cycle of the Suzuki–Miyaura coupling between PhBr and PhB(OH)3− with four different palladium monophosphine catalysts derived from Pd(PMe3)2, Pd(P(CF3)3)2, Pd(PPh3)2 and Pd(PtBu3)2. All the steps of the reaction have been studied and the differences between the ligands have been analyzed; special attention has been devoted to the ligand dissociation and catalyst regeneration processes, as well as the typical cross-coupling steps of oxidative addition, transmetallation and reductive elimination. Multiple linear regressions of the computationally derived energy barriers have been carried out in order to quantify the ligand effects of the different phosphines on the key steps of the reaction. These ligand effects, relevant to the catalytic activity, are described in terms of the phosphine donor/acceptor and steric features. The regression models show that oxidative addition is mainly governed by electronic effects whereas the transmetallation and the reductive elimination processes are controlled by a mixture of both ligand effects. For transmetallation, electron-withdrawing ligands lower the energy barrier. |
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