Extended hypervalent E′⋯E–E⋯E′ 4c–6e (E, E′ = Se, S) interactions: structure, stability and reactivity of 1-(8-PhE′C10H6)EE(C10H6E′Ph-8′)-1′

Abstract

The structure, stability and reactivity of E′⋯E–E⋯E′ (E₂E′₂) 4c–6e are examined employing naphthalene 1,8-positions in 1-(8-PhE′C₁₀H₆)EE(C₁₀H₆E′Ph-8′)-1′ [1 (E = Se, E′ = S), 2 (E = S, E′ = Se), 3 (E = E′ = Se) and 4 (E = E′ = S)], together with 1-C₁₀H₇EEC₁₀H₇-1′ [5 (E = Se) and 6 (E = S)]. Linear alignments of four Se₂S₂ atoms in 1 and 2 are confirmed by the X-ray analysis. 1 was not reduced by sodium borohydride, whereas 2 was, contrary to the expectation. Similarly, E–E in 3, 5 and 6 were cleaved, whereas that in 4 was not, when allowed to react with NaBH₄ in aqueous THF. The reactivity of the E–E bonds in E₂E′₂ in 1–4 is not controlled by the central E atoms but by the outside E′ atoms. Quantum chemical (QC) calculations are performed on 1-(8-MeE′C₁₀H₆)EE(C₁₀H₆E′Me-8′)-1′ (13–16: models of 1–4, respectively), 5 and 6, together with the related species. Conformers having E₂E′₂ 4c–6e (abbreviated by BA) are the global minima for 13, 15 and 16, which reproduces the observed structures: BA must be stabilized by the formation of E₂E′₂ 4c–6e. 14 (AB) with double n(S)⋯σ*(Se–C) 3c–4e interactions is the global minimum, which shows that σ*(Se–C) plays a crucial role to stabilize the 3c–4e in AB. The novel reactivity of E–E is considered based on the QC calculations.