Intramolecular Methylacridan-Methylacridinium Complexes with a Phenanthrene-4,5-diyl or Related Skeleton: Geometry-Property Relationships in Isolable C-H Bridged Carbocations

摘要

The isolation and low-temperature X-ray analyses of a series of intramolecular methylacridan-methylacridinium complexes have been achieved. The two chromophores are in close proximity due to an arylene spacer, such as a phenanthrene-4,5-diyl or biphenyl-2.2'-diyl unit. These bridged carbocations prefer the C-H localized structure both in solution and in the solid state. The bridging hydrogen atom undergoes a facile intramolecular hydride shift from one carbon atom to another in solution, and the energy barrier is linearly correlated with the intramolecular C center dot center dot center dot C+ distance in the solid state geometry, as determined by single-crystal X-ray analyses. By extrapolation from the data, the delocalized three-center bond of [C-H-C](+) would be formed when the C center dot center dot center dot C+ distance is less than 2.7 angstrom.