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Pure Appl. Chem., 2010, Vol. 82, No. 4, pp. 1033-1044

Published online 2010-03-20

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

Takanori Suzuki1*, Takashi Takeda1, Yasuyo Yoshimoto1, Takayuki Nagasu1, Hidetoshi Kawai1,2 and Kenshu Fujiwara1

1 Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan
2 PRESTO, Japan Science and Technology Agency (JST), Kawaguchi, Saitama, Japan

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.