Theoretical Insights into Mechanisms for Copper(I)-Catalyzed C–P Coupling of Diarylphosphines with Aryl Halides: A Combined Solvent and Ancillary Ligand Effect on the Identity of Active Catalyst and Reaction Mechanism

Abstract

A theoretical study on reaction mechanisms for copper-catalyzed Ullmann-type C–P coupling of diphenylphosphine with aryl halides is reported herein. The equilibria and consequent relative concentrations of possible copper species in the reaction solution were evaluated to determine probable active catalytic species in the presence of several typical ancillary ligands in toluene and DMSO solvents. Subsequently, reactivity of these key copper species with aryl halides were studied in the context of commonly proposed mechanisms for copper(I)-catalyzed Ullmann reactions, including oxidative addition/reductive elimination, σ-bond metathesis, single electron transfer (SET), and halogen atom transfer (HAT) mechanisms. On the basis of these studies, we propose that for phenanthroline and 1,2-ethylenediamine types of bidentate ligands, the active catalyst should be the neutral form LCu(I)-PPh2 in nonpolar toluene, while the Cu(PPh2)2– anion should be significant in highly polar DMSO. In contrast, for phosphine typ...