Thermal Transformation of Ring-Opened [2+2] C₆₀ Dimer into a Wide-Bridged C₁₂₀ Isomer. A Computational Evaluation of Fulvalene-Naphthalene Rearrangements

Abstract

As a continuation of the studies on thermal transformation of the [2+2] C₆₀ dimer (1), the consequence of the pyracylene-rearrangement-like valence isomerization of the fulvalene partial structure at the bridge of the ring-opened product from 1, namely 2, was searched by dynamic reaction coordinate /AM1 semiempirical MO calculations. It is predicted that the fulvalene bridge of 2 rearranges into naphthalene partial structure by the concerted ‘in-plane’ mechanism to give a wide-bridged C₁₂₀ intermediate having twenty five-membered rings and two ten-membered rings (3). The computed energy of activation (145 kcal/mol) is 40 kcal/mol lower than those computed for pyracylene rearrangements. In contrast, the recently reported analogous rearrangement of indigo (13) to dibenzonaphthyridindione (14) is computed to occur by the stepwise ‘sp³’ mechanism.

Notes

There is some controversy as to the computed length of this bond. We will address this problem elsewhere.

When C-H vibrational modes were included in the dynamic reaction coordinate analysis, a pathway leading to azulene was found: Ōsawa, E. and Honda, K. manuscript in preparation.

These names were coined by Murry et al., ref. 6.

MOPAC93 version 6.01 by J. J. P. Stewart was obtained from the Japan Chemistry Program Exchange, 1–7–12 Nishine-Nishi, Tsuchiura 300, Japan (FAX x-81–298–30–4162), program No. P049.