Cross-Bridging Reaction of 5,20-Diethynyl Substituted Hexaphyrins to Vinylene-Bridged Hexaphyrins
2007-01-24T00:00:00Z (GMT) by
5,20-Diethynyl substituted hexaphyrins(18.104.22.168.1.1) undergo a thermal or spontaneous cross-bridging reaction to provide trans-vinylene-bridged hexaphyrins, probably through strongly folded conformations. Facile aromatic−antiaromatic switching of vinylene-bridged hexaphyrins has been demonstrated upon two-electron redox processes. Curiously, a resonance contributor of the vinylene-bridged hexaphyrins is regarded as diazaannulenodiazaannulene but its contribution should be minor because of the perpendicular geometry of the bridge. Vinylene-bridged hexaphyrin serves as an effective ligand that coordinates two zinc(II) ions using the central vinylene double bond in a η2-fashion along with the three pyrrolic nitrogen atoms.