Parallel and perpendicular stacking of ferrocene rings.: Syntheses, X-ray structures, and electrochemistry of 1,8-bis-[1-(1′-phenylthio)ferrocenyl]naphthalene and 8,8′-bis-[1-(1′-phenylthio)ferrocenyl]-1,1′-binaphthyl

The parallel and perpendicular stacking of ferrocene rings in 1,8-bis-[1-(1′-phenylthio)ferrocenyl]naphthalene (1) and 8,8′-bis-[1-(1′-phenylthio)ferrocenyl]-1,1′-binaphthyl (2), respectively, were investigated. They were synthesized from the Suzuki coupling of 2,4,6-tris(1′-phenylthio-1-ferrocenyl)boroxin (3) with 1,8-diiodonaphthalene and 1,8-diiodo-1,1’-binaphthyl, respectively. Their structures were confirmed by single-crystal X-ray analyses. The two cyclopentadienyl (Cp) rings (C9C13 and C19C23) of the two respective ferrocenes Fe(1) and Fe(2) of 1 are not parallel, but are 21.3° away from parallel. The distance between the centroids of these two Cp rings is 3.336 Å. The two Cp rings (C9C13 and C9′C13′) of the two respective ferrocenes Fe(1) and Fe(2) of 2 are not perpendicular, but have a dihedral angle of 49.9°, and the distance between two centroids of these two Cp rings is 5.255 Å. The electrochemical behaviour of 1 and 2 in dichloromethane solution shows that they undergo reversibly two ferrocene-centred one-electron oxidations to the corresponding dications. The separation between the two anodic processes is greater for 1 with respect to 2, but the absolute value of the separation significantly depends upon the nature of the supporting electrolyte. In the presence of the classical [NBu4][PF6] the ΔE°′ value is 0.15 V for 1 and 0.07 V for 2. In the presence of the new [NBu4][B(C6F5)4] the ΔE°′ value increases to 0.45 V for 1 and 0.13 V for 2. In view of the low ion-pairing ability of the [B(C6F5)4]− counteranion, it is conceivable that the increased intramolecular electronic communication might essentially arise from the increased electrostatic repulsion (or through-space interaction) following the 0/+/2+ redox changes rather than from through-bond electron delocalization.