Intramolecular triarylmethane-triarylmethylium complex: Generation, properties, and X-ray structure of a C–H bridged carbocation

Abstract

A series of title carbocations was generated and isolated as stable salts. X-ray analyses revealed a preference for an unsymmetric structure in which the bridging hydrogen is localized on one of the two triarylmethane units. NMR spectroscopy showed a similar preference in solution. The bridging hydrogen fluctuates between the two chromophores in solution, and the energy barrier for the H shift is linearly correlated with the C···C+ separation determined by X-ray. According to an extrapolation, the energy barrier should decrease when the C···C+ separation is less than 2.7 Å, which suggests a new model for isolable pure organic species with a three-center–two-electron bond.