Enhancing Electron Accepting Ability of Triarylboron via π-Conjugation with 2,2‘-Bipy and Metal Chelation: 5,5‘-Bis(BMes2)-2,2‘-bipy and Its Metal Complexes

Abstract

The synthesis of a new diboron compound, 5,5‘-bis(BMes2)-2,2‘-bipy (B2bipy, 1), has been accomplished. The conjugation of the 2,2‘-bipy unit with the two BMes2 groups in 1 has been found to greatly enhance the electron-accepting ability of the boron centers, compared to the biphenyl analogue. 1 is an effective chelate ligand for metal ions and three metal complexes; namely, [CuI(B2bipy)(PPh3)2][BF4], 2, PtII(B2bipy)Ph2, 3a, and PtII(B2bipy)Me2, 3b, have been synthesized. The binding of metal ions to B2bipy was found to further significantly increase the electron-accepting ability/Lewis acidity of the boron centers. Cyclic voltammetry diagrams revealed that the free ligand and all three complexes display two reversible reduction peaks that are separated by 0.31−0.40 V. The first reduction potential (E1/2) for 1, 2, 3a, and 3b was found to be −1.69, −1.36, −1.34, and −1.38 V, respectively, versus FeCp2+/0 in DMF, which supports that the electron-accepting ability of the metal complexes is much greater than ...