Structures in 8-(methylselanyl)-1-(methylseleninyl)- and 1,8-bis(methylseleninyl)naphthalenes: Transition states involving simultaneous rotation around SeC bonds, together with stable structures

The energy profile of 8-(methylselanyl)-1-(methylseleninyl)naphthalene (1) is revealed to clarify how the Se(O)Me and SeMe groups control the stereochemistry of 1, through the nonbonded Se-SeO interaction. Six stable structures (SSs) and eight transition states (TSs) are optimized for 1. Frequency analysis is carried out for all SSs and TSs. The global minimum of 1 is the trans-form of 1 (1 (t-AA)), which reproduces the structure determined by the X-ray crystallographic analysis. Three Se-SeO atoms in 1 (t-AA) are on the naphthyl plane and two Me groups are in trans. Next stable one is the cis-form (1 (c-AC′)). Motions in the imaginary frequencies of six TSs correspond to the rotation around an SeCNap bond, whereas those of the two to the simultaneous rotations around the two SeCNap bonds. Attractive interactions must play an important but additional role in the simultaneous rotations in TS. The observed structure in 1,8-bis(methylseleninyl)naphthalene (2) is also reproduced by the global minimum, where the four OSe-SeO atoms align linearly. NBO analysis reveals that σ(3c-4e) of the nonbonded Se-SeO interaction controls the structure of 1 whereas σ(4c-4e) of the OSe-SeO interaction will not in 2.