1-ARYL-8-TROPYLIONAPHTHALENE PERCHLORATES - SYNTHESIS AND INTRA-MOLECULAR CHARGE-TRANSFER INTERACTION

A series of 1-aryl-8-tropylionaphthalene cations [aryl = phenyl (4a), p-methylphenyl (4b), m, m-dimethylphenyl (4c), p-methoxyphenyl (4d), p-(trifluoromethyl)phenyl (4e), and m, m-bis(trifluoromethyl)phenyl (4f)] have been synthesized by nickel(II)-catalyzed coupling of 1-bromo-8-cycloheptatrienylnaphthalene with the corresponding arylmagnesium halides followed by hydride abstraction. The 1H NMR spectra of 4a-f indicated that the two aromatic rings at the peri positions are in a face-to-face arrangement. The absorption band at 373 nm observed in the electronic spectrum of 4a in acetonitrile was assigned to the intramolecular charge-transfer band between the phenyl and tropylium rings based on the solvent and substituent effects. This intramolecular electronic interaction results in stabilization of the cation 4a by 2.1 pKR+ units and the increase in its reduction potential by 0.182 V as compared with the reference cation, 1-tropylionaphthalene (5). A better linear correlation was obtained when the values of ppKR+ and reduction potential for 4a-f were plotted against the substituent constant σm+ rather than against σp+. This result together with the substituent effect upon the 1H NMR chemical shift of the tropylium ring protons suggests that the electronic effect of the substituents would be transmitted inductively through the σ overlap of p orbitals of the two aromatic rings facing each other. © 1979, American Chemical Society. All rights reserved.