Synthesis of Diaryl Ethers by CuI-Catalyzed C-O Bond Formation via Ullman Coupling: Assessing the Reactivity of Aryl Halides

Using cuprous iodide as the catalyst, aryl halides reacted with phenols to form diaryl ethers. The reaction conditions were optimized: aryl halides (1 equiv) reacted with phenol (1 equiv) at 130 °C in DMF for 16 h with cuprous iodide (10 mol %), cesium carbonate (2.5 equiv) as the base, and tetramethylenediamine (5 mol %) as the ligand. Under the optimum conditions, reaction conversion with time was summarized. The structural parameters of four types of aryl halides and the ionization energy of various C-X bond lengths in all aryl halides-CuI π-complexes were calculated at the B3LYP/LANL2MB level by using the Gaussian 03 program and the corresponding Ullman reaction conversion was determined by HPLC. Results suggested that different relationships existed between reactivity and the energy of the lowest unoccupied molecular orbital ELUMO, mean polarizability α and dipole moment μ. Both experimental and theoretical results, all displayed Ullman coupling reactivity order of the four aryl halides: fluorobenzene << chlorobenzene < bromobenzene < iodobenzene.