Electrochemistry, Charge Transfer Properties, and Theoretical Investigation of a Macrocyclic Boronate Dimer of 1′,1‴-Biferrocenediboronic Acid and Related Ferrocenyl Boronate Complexes
The target compound of this study is the macrocyclic tetraferrocenyl boronate complex CP2C, which has two types of metal connections (i.e., (FeCpCpFeII)-Cp-II and FeIICpBO2C5H8O2BCpFeII (Cp = cyclopentadienyl)) in the finite structure (C = 1',1?-biferrocenediboronic acid, P = pentaerythritol). The electrochemical behavior of CP2C in dichloromethane was compared with that of the related boronate complexes APA and BP2B, having (FeCpBO2C5H8O2BCpFeII)-Cp-II, and Cester, having FeIICpCpFeII. The effects of the counteranion of the supporting electrolyte on potential splitting revealed that CP2C exhibits an intrabiferrocenyl through-bond interaction through the CpCp ligand, as well as an interbiferrocenyl through-space interaction across the CpBO2C5H8O2BCp ligand. Chemical oxidation of CP2C with AgSbF6 produced the one- and two-electron-oxidized species CP2C+ and CP2C2+, which exhibit intervalence charge transfer transition bands through the CpCp ligand in the near-infrared region, giving one and two valence isomers, respectively. DFT calculations revealed the charge distribution of CP2C2+; the positive charges are localized on each biferrocenium unit, especially on the longer diagonal, to minimize the electrostatic repulsion over the CpBO2C5H8O2BCp ligand.