A Novel Carbodication Composed of Two Tris(bicyclo[2.2.2]octeno)tropylium Units Connected by a Triple Bond: Synthesis, Structure, and Properties
摘要:
The titled dication, bis[tris(bicyclo[2.2.2]octeno)tropyliumyl] acetylene dication 3, which is the first example of the acetylene having two tropylium ion units at both ends, has been synthesized by stepwise introduction of the tris(bicyclo[2.2.2]octeno)cycloheptatrienyl unit to acetylene followed by hydride abstraction. The results of X-ray crystallography indicated that the two tropylium rings are twisted with each, other by the angle of 44 degrees and the tropylium ring is slightly bent into a boat form. The dication 3 was neutralized in 50% aqueous acetonitrile via two steps at the pH values of 7.0 and 11.5, which correspond to the pK(R+) values of the dictation and the half-neutralized monocation, respectively. Thus, the dication 3 is 6 pK(R+) units destabilized compared with the corresponding monocation (pK(R+) 13.0) due to the intramolecular electrostatic repulsion of the positive charge. The cyclic voltammetry indicated that the dication 3 undergoes two reversible one-electron reductions consecutively in dichloromethane. The electrochemical reduction of 3 as well as chemical reduction with zinc powder in dichloromethane-acetonitrile afforded a blue solution of the corresponding cation radical 3(.+), but not the diradical, as shown by ESR experiments.
The titled dication, bis[tris(bicyclo[2.2.2]octeno)tropyliumyl] acetylene dication 3, which is the first example of the acetylene having two tropylium ion units at both ends, has been synthesized by stepwise introduction of the tris(bicyclo[2.2.2]octeno)cycloheptatrienyl unit to acetylene followed by hydride abstraction. The results of X-ray crystallography indicated that the two tropylium rings are twisted with each, other by the angle of 44 degrees and the tropylium ring is slightly bent into a boat form. The dication 3 was neutralized in 50% aqueous acetonitrile via two steps at the pH values of 7.0 and 11.5, which correspond to the pK(R+) values of the dictation and the half-neutralized monocation, respectively. Thus, the dication 3 is 6 pK(R+) units destabilized compared with the corresponding monocation (pK(R+) 13.0) due to the intramolecular electrostatic repulsion of the positive charge. The cyclic voltammetry indicated that the dication 3 undergoes two reversible one-electron reductions consecutively in dichloromethane. The electrochemical reduction of 3 as well as chemical reduction with zinc powder in dichloromethane-acetonitrile afforded a blue solution of the corresponding cation radical 3(.+), but not the diradical, as shown by ESR experiments.