How does non-covalent Se⋯SeO interaction stabilize selenoxides at naphthalene 1,8-positions: structural and theoretical investigations

Abstract

Bis-selenides (LL), such as 8-[MeSe(X)]-1-[MeSe(Z)]C₁₀H₆ (1 (LL)), 8-[EtSe(X)]-1-[EtSe(Z)]C₁₀H₆ (2 (LL)), 8-[p-YC₆H₄Se(X)]-1-[MeSe(Z)]C₁₀H₆ (3 (LL)) and 8-[p-YC₆H₄Se(X)]-1-[p-YC₆H₄Se(Z)]C₁₀H₆ (4 (LL)) were oxidized with ozone at 0 °C, where (X, Z) = (lone pair, lone pair) for LL. Bis-selenoxides, 1 (OO), 3 (OO) and 4 (OO) where (X, Z) = (oxygen, oxygen), were obtained in the oxidation of 1 (LL), 3 (LL) and 4 (LL), respectively, via corresponding selenide-selenoxides, 1 (LO), 3 (LO) and 4 (LO), respectively. A facile Se–C bond cleavage was observed in 2 (LL). The structures of 1 (LO) and 1 (OO) were determined by the X-ray analysis. Three Se⋯SeO atoms in 1 (LO) and four OSe⋯SeO atoms in 1 (OO) align linearly. While the non-covalent Se⋯SeO 3c–4e interaction operates to stabilize 1 (LO), the non-covalent OSe⋯SeO 4c–4e interaction would not stabilize 1 (OO). The 3c–4e interaction must play an important role to control the stereochemistry of selenoxides. The 8-G-1-[MeSe(OH)₂]C₁₀H₆ (n (OH·OH)) are the key intermediates in the racemization of 8-G-1-[MeSe(O)]C₁₀H₆ (n (O)) in solutions, where G = SeMe (1), H (5), F (6), Cl (7) and Br (8). Energies of n (OH·OH), relative to n (O), are evaluated based on the theoretical calculations. G of SeMe is demonstrated to operate most effectively to protect from racemization of selenoxides among n = 1 and 5–8, since the relative energies for G of cis- and trans-SeMe are largest.