In the search for new ligands for the Ullmann diaryl ether synthesis, permitting the coupling of electron-rich aryl bromides at relatively low temperatures, 56 structurally diverse multidentate ligands were screened in a model system that uses copper iodide in acetonitrile with potassium phosphate as the base. The ligands differed largely in their performance, but no privileged structural class could be identified.
Otto, N., & Opatz, T. (2012). Screening of ligands for the Ullmann synthesis of electron-rich diaryl ethers. Beilstein Journal of Organic Chemistry, 8, 1105–1111. https://doi.org/10.3762/bjoc.8.122