Site‐Directed Dimerization of Bowl‐Shaped Radical Anions to Form a σ‐Bonded Dibenzocorannulene Dimer

Designed site‐directed dimerization of the monoanion radicals of a π‐bowl in the solid state is reported. Dibenzo[a,g]corannulene (C 28 H 14 ) was selected based on the asymmetry of the charge/spin localization in the C 28 H 14 .− anion. Controlled one‐electron reduction of C 28 H 14 with Cs metal in diglyme resulted in crystallization of a new dimer, [{Cs + (diglyme)} 2 (C 28 H 14 −C 28 H 14 ) 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 C 28 H 14 .− bowls (1.560(8) Å) measured at −143 °C does not significantly change upon heating of the crystal to +67 °C. The single σ‐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)° and 173.5(5)°. A systematic theoretical evaluation of dimerization pathways of C 28 H 14 .− radicals confirmed that the trans‐isomer found in 1 is energetically favored.