Electrochemistry, Charge Transfer Properties, and Theoretical Investigation of a Macrocyclic Boronate Dimer of 1′,1‴-Biferrocenediboronic Acid and Related Ferrocenyl Boronate Complexes

Abstract

The target compound of this study is the macrocyclic tetraferrocenyl boronate complex CP 2 C, which has two types of metal connections (i.e., Fe II –CpCp–Fe II and Fe II –CpBO 2 C 5 H 8 O 2 BCp–Fe II (Cp = cyclopentadienyl)) in the finite structure ( C = 1′,1‴-biferrocenediboronic acid, P = pentaerythritol). The electrochemical behavior of CP 2 C in dichloromethane was compared with that of the related boronate complexes APA and BP 2 B, having Fe II –CpBO 2 C 5 H 8 O 2 BCp–Fe II, and Cester, having Fe II –CpCp–Fe II . The effects of the counteranion of the supporting electrolyte on potential splitting revealed that CP 2 C exhibits an intrabiferrocenyl through-bond interaction through the CpCp ligand, as well as an interbiferrocenyl through-space interaction across the CpBO 2 C 5 H 8 O 2 BCp ligand. Chemical oxidation of CP 2 C with AgSbF 6 produced the one- and two-electron-oxidized species CP 2 C + and CP 2 C 2+, 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 CP 2 C 2+; the positive charges are localized on each biferrocenium unit, especially on the longer diagonal, to minimize the electrostatic repulsion over the CpBO 2 C 5 H 8 O 2 BCp ligand.