Syntheses, Properties, and Redox Behaviors of Di(1-azulenyl)ferrocenylmethyl Cations and 1,3-Bis[(1-azulenyl)ferrocenylmethylium]azulene Dication

Abstract

The titled stable mono- and dications, di(1-azulenyl)ferrocenylmethyl cation ( 5a ) and its 3,3‘-dimethyl ( 5b ) and 3,3‘,6,6‘-tetra- tert -butyl ( 5c ) derivatives, as well as the corresponding dication, 1,3-bis[(1-azulenyl)ferrocenylmethylium]azulene dication ( 6 ), were prepared by hydride abstraction of the corresponding hydrocarbons, di(1-azulenyl)ferrocenylmethanes ( 7a − c ) and 1,3-bis[(1-azulenyl)ferrocenylmethyl]azulene ( 8 ), and their properties were fully characterized. These cations showed extreme stabilities with high p K R + values. The values of 5a − c were determined in 50% aqueous acetonitrile to be 12.2 ± 0.3, 12.2 ± 0.4, and 12.5 ± 0.4, respectively. The two cation units in the dication 6 were neutralized via two steps at the pH values of 8.8 ± 0.5 and 11.6 ± 0.5, which correspond to the p K R + values of the dication and the half-neutralized monocation, respectively. The redox properties of the ferrocene rings in the mono- and dications ( 5a − c and 6 ) were barely changed by the connection with extremely stable di(1-azulenyl)methylium units. The cyclic voltammetries of 5a − c indicated that these cations undergo a reversible one-electron oxidation (+0.42 to +0.47 V vs Ag/Ag + ), as well as a reversible one-electron reduction (−0.76 to −0.87 V) in acetonitrile. Similarly, the dication 6 showed a reversible one-step, two-electron oxidation (+0.51 V), which was ascribed to the oxidation of two ferrocene rings.