Intramolecular Binaphthyl Formation from Radical Cations of Tri-1-naphthyl Phosphate and Related Compounds in Photoinduced Electron-Transfer Reactions Sensitized by 9,10-Dicyanoanthracene.
The photoinduced electron transfer of tri-1-naphthyl phosphate and related compounds sensitized by 9,10-dicyanoanthracene (DCA) in acetonitrile produces 1,1'-binaphthyl and the corresponding biaryl. The quenching rate constant of the DCA fluorescence is calculated to be equal to the diffusion-controlled rate constant from the Stern-Volmer analysis and the fluorescence lifetime measurement. The free energy change calculated from the redox potentials and excitation energy of the singlet excited DCA indicates that the quenching process occurs exergonically to give the tri-1-naphthyl phosphate radical cation and DCA radical anion through electron transfer from tri-1-naphthyl phosphate to the singlet excited DCA at the diffusion-controlled rate. On the basis of spectroscopic and kinetic studies with laser flash photolysis, pulse radiolysis, and gamma-radiolysis, the radical cation of tri-1-naphthyl phosphate forms an intramolecular pi-dimer radical cation with face-to-face interaction between the two naphthyl groups within 8 ns of the electron pulse. The 1,1'-binaphthyl radical cation is eliminated at the rate constant of k(r) = 5.3 x 10(5) s(-)(1) from the intramolecular pi-dimer radical cation. Branching ratios of the reaction pathways are estimated for the reactive intermediates such as the tri-1-naphthyl phosphate radical cation and its intramolecular pi-dimer radical cation from the rate constants and quantum yields. The electron-withdrawing character of the P(O) group in the O-P(O)-O spacer is responsible for the elimination of the binaphthyl radical cation. The DCA-sensitized photoinduced electron-transfer reaction of the tri-1-naphthyl phosphate is compared with the direct photoreaction.
Nakamura
Mitsunobu
M
Department of Engineering Science, Himeji Institute of Technology, Shosha 2167, Himeji, Hyogo 671-2201, Japan, and The Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan.
Dohno
Reizo
R
Majima
Tetsuro
T