'I-I-NMR Spectra and Reaction of [n]Frrocenophan-6-ols and -7-ols in Triflu oroacetic Acid -Formation of Ferrocenophane 6-Carbocations

Abstract

The 1H-NMR spectra of several [3]ferrocenophane-6-ols [3], 4 lferrocenophane-6-ols[4] and 4 Nerrocenophane-7-ols [5] in trifluoroacetic acid-d (TFA-d) were measured, and the structures of the compounds obtained by hydrolysis of the solutions in TFA-d were examined. The spectra of [3] and [4] indicated formation of stable 6-carbocations; the chemical shifts of the 6-methine and 6-methyl protons, the splittings and coupling constants of the cyclopentadienyl rings, and the long-range spin-spin coupling constants between the 6-methine and ring protons are similar to those_ of 1-ferrocenylalkyl cations. The cationic species were formed with retention of the geometric structures of the alcohols. Rearrangement of the cationic center from the 7-position to the 6-position by 1, 2-hydride shift was observed in the strong acid for [5]containing a tertiary OH. Hydrolysis of these solutions gave the corresponding 6-ols, which were dissolved in the acid to show the same sp ectra as 7-ols in TFA-d. Dissolving [5], which contains a secondary OH, in the acid did not lea d to carbocations, but formation of the species stabilized by participation of ferrocene moi ety was suggested.