Synthesis and properties of tetraphenyltriafulvene

Abstract

The reaction of the 1,2-diphenylcyclo propenium ion ( 5) with benzhydrylmagnesium bromide exclusively affords 1,2-diphenyl-3-benzhydrylcyclo propene ( 4), though the reaction of 5 with benzhydryllithium in the presence of lithium chloride yields no cyclopropene 4 but 1,3-diphenyl-3-benzhydryl-cyclopropene ( 6) via the intermediate formation of 1,2-diphenyl-3-chlorocyclopropene ( 7). The hydride abstraction from the cyclopropene 4 followed by deprotonation gives tetraphenyltriafulvene ( 2) as dark red crystals. The 13C NMR spectrum, as well as a bathochromic shift of the longest-wavelength absorption in the electronic spectrum with decrease in solvent polarity, indicates a considerable contribution of the dipolar structure at the ground state of 2. The cyclic voltammetry on 2 reveals that 2 can be readily oxidized to a stable cation radical and a less stable dication. The cation radical was also generated by chemical oxidation with silver tetrafluoroborate or antimony pentafluoride, and was investigated by ESR spectroscopy.