Synthesis of molecular motors incorporating para-phenylene-conjugated or bicyclo[2.2.2]octane-insulated electroactive groups.

The insulating role of the bicyclo[2.2.2]octane fragment has been theoretically evaluated by comparing the electronic coupling parameter (V(ab)) in 1,4-bis(ferrocenyl)benzene (1) and 1,4-bis(ferrocenyl)bicyclo[2.2.2]octane (2). The geometries were optimized by DFT and an extended Hückel calculation was performed to evaluate V(ab) by the dimer splitting method. The calculations showed a 12-fold decrease of the electronic coupling from 60 meV for 1 to 5 meV for 2. The second part describes the synthesis of two potential molecular motors with one incorporating the insulating bicyclo[2.2.2]octane fragment. These molecules are based on a ruthenium complex bearing a tripodal stator functionalized to be anchored onto surfaces. The ferrocenyl electroactive groups and the cyclopentadienyl (Cp) rotor are connected through a p-phenylene spacer (5) or through a spacer incorporating an insulating bicyclo[2.2.2]octane moiety (6).