Reaction of the 1,8-bis(diphenylmethylium)naphthalenediyl dication with fluoride: formation of a cation containing a C-F-->C bridge.
Additional Document Info
Treatment of 1,8-bis(diphenylhydroxymethyl)naphthalene with a mixture of [HBF(4)](aq) and (CF(3)CO)(2)O affords the corresponding dication, 1,8-bis(diphenylmethylium)naphthalenediyl (1(2+)), which was isolated as the [BF4]- salt. This dication has been fully characterized, and its structure has been studied computationally. The (13)C NMR resonance of the methylium centers appears at 207.7 ppm. As indicated by an X-ray single-crystal analysis, the vicinal methylium centers are separated by 3.112(4) A. Dication (1(2+)) reacts with fluoride to afford [1-F]+ which has been isolated as the [BF4]- salt. The fluorine atom of [1-F](+) is connected to one of the former methylium centers through a typical C-F bond of 1.424(2) A and forms a long interaction of 2.444(2) A with the other methylium center. While the structure of [1-F]+ can be largely accounted for by considering a simple methylium formulation, density functional calculations followed by an Atom In Molecules analysis as well as a calculation of the Boys localized orbitals indicate that the long C-F interaction of 2.444(2) A corresponds to a dative bond. Hence, formulation of [1-F]+ as an unsymmetrical fluoronium must also be considered. As indicated by 1H NMR spectroscopy, the structure of this ion is fluxional; the fluorine atom oscillates between the former methylium centers with apparent activation parameters of DeltaH++ = 52(+/-3) kJ mol(-1) and DeltaS++ = -18(+/-9) J K(-1) mol(-1) as derived from line shape analysis. This dynamic process, which has also been studied theoretically by B3LYP density functional theory and Mller-Plesset second-order perturbation theory methods, involves symmetrical fluoronium ions as low-energy transition states.