Synthesis of Molecular Motors Incorporating para‐Phenylene‐Conjugated or Bicyclo[2.2.2]octane‐Insulated Electroactive Groups

Abstract

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).

Nonconjugated Hydrocarbons as Rigid‐Linear Motifs: Isosteres for Material Sciences and Bioorganic and Medicinal Chemistry

“…DFT was used to optimize geometries and extended Hückel calculations were employed to calculate V ab by the dimer splitting method. Results of the calculations showed a 12‐fold decrease in electronic coupling with the BCO derivative (Figure ) …”

“…Results of the calculationss howeda12-fold decreasei ne lectronic coupling with the BCO derivative ( Figure 20). [232] Following this, ap otentials tar-shaped molecular motor 181 was synthesized that incorporates the BCO fragment. [233] The molecule is based on ar uthenium complex that bears at ripodal statorf unctionalized with ester groups to be anchored onto oxide surfaces.…”

Scorpionate Hydrotris(indazolyl)borate Ligands as Tripodal Platforms for Surface‐Mounted Molecular Gears and Motors

“…The desired piano‐stool ruthenium complex 9 , featuring a scorpionate ligand, was obtained in 20 % isolated yield. At that stage, the κ 3 ‐ N , N′ , N′′ coordination mode of the tripodal ligand was unambiguously confirmed by an X‐ray crystal structure …”

“…Replacing a bis‐ethynyl bridge with a trans ‐bisacetylide platinum(II) moiety resulted in a fourfold decrease in the calculated V ab parameter, thereby confirming the insulating nature of the latter group in accordance with the σ‐character of the Pt–C bonds . Comparison of systems incorporating either a p ‐phenylene or a bicyclo[2.2.2]octyl linker showed attenuation of the electronic communication between the iron centers by a factor of 12 in the case of the saturated alkyl scaffold …”

A family of electron-triggered molecular motors based on aromatic building blocks

“…In order to obtain a better insulation, we also synthesized the molecular motor 6 (Scheme 3) where the EGs are separated by bicyclo [2.2.2]octane spacers [19]. DFT and extended Hückel calculations showed in this case a 12-fold decrease of the electronic coupling.…”