Site-Directed Dimerization of Bowl-Shaped Radical Anions to Form a sigma-Bonded Dibenzocorannulene Dimer

摘要

Designed site-directed dimerization of the monoanion radicals of a pi-bowl in the solid state is reported. Dibenzo[a,g]corannulene (C28H14) was selected based on the asymmetry of the charge/spin localization in the C28H14 center dot- anion. Controlled one-electron reduction of C28H14 with Cs metal in diglyme resulted in crystallization of a new dimer, [{Cs+(diglyme)}(2)(C28H14-C28H14)(2-)] (1), as revealed by single crystal X-ray diffraction study performed in a broad range of temperatures. The C-C bond length between two C28H14 center dot- bowls (1.560(8)angstrom) measured at -143 degrees C does not significantly change upon heating of the crystal to +67 degrees C. The single sigma-bond character of the C-C linker is confirmed by calculations. The trans-disposition of two bowls in 1 is observed with the torsion angles around the central C-C bond of 172.3(5)degrees and 173.5(5)degrees. A systematic theoretical evaluation of dimerization pathways of C28H14 center dot- radicals confirmed that the trans-isomer found in 1 is energetically favored.