Intramolecular triarylmethane-triarylmethylium complexes with a naphthalene-1,8-diyl skeleton: isolation, structure, and reactivities of the C--H-bridged carbocations.

Isolation and low-temperature X-ray analyses of intramolecular triarylmethane-triarylmethylium complexes with a naphthalene-1,8-diyl-type skeleton have been achieved. These bridged cations prefer a C--H localized structure both in solution and in the solid state. The bridging hydrogen undergoes a facile intramolecular 1,5-hydride shift from one carbon to another in solution. The C--H delocalized geometry is suggested to be the transition-state structure of the degenerate rearrangement. Charge-transfer interaction from the triarylmethane to the triarylmethylium units is evident in the electronic spectra. This interaction stabilizes the present cations. Low reactivity toward Brønsted acids indicates that these species are not the reaction intermediates in the acid-assisted long-bond cleavage of 1,1,2,2-tetraarylacenaphthene derivatives.