Bismuth⋯π arene versus bismuth⋯halide coordination in heterocyclic diorganobismuth(iii) compounds with transannular N→Bi interaction

Abstract

New diorganobismuth(III) bromides of type [RN(CH₂C₆H₄)₂]BiBr [R = C₆H₅CH₂ (1), C₆H₅CH₂CH₂ (2), and CH₃OCH₂CH₂ (3)], based on the heterocyclic butterfly-like tetrahydro-dibenzo[c,f][1,5]azabismocine framework, were prepared starting from the corresponding RN(CH₂C₆H₄Br-2)₂ in a succession of reactions including ortho-lithiation and treatment of the dilithio derivative with BiBr₃ in a 1 : 1 molar ratio. Further exchange reactions between bromides and appropriate metal halides or ammonium fluoride resulted in the formation of [RN(CH₂C₆H₄)₂]BiX [X = Cl and I for R = C₆H₅CH₂ (4 and 5) and C₆H₅CH₂CH₂ (6 and 7) and X = F (8), Cl (9), and I (10) for R = CH₃OCH₂CH₂]. All ten compounds were structurally characterized in solution by NMR and in the solid state by single-crystal X-ray diffraction. Strong transannular N→Bi interactions were observed in all the investigated diorganobismuth(III) halides, thus giving rise to hypervalent 10–Bi–4 species in 1, 2, 4–7 and 12–Bi–5 species in 3, 8–10, where the oxygen atom in the pendant arm is intramolecularly coordinated to bismuth. The molecules are associated in dimeric units by strong Bi⋯π arene interactions in 3, 4, and 10 (approx. 3.50 Å) and by Bi⋯X interactions in 1, 5, and 7. Bromide 1, chloride 4, and iodide 5 are isostructural, but stronger polarization of the Bi–Cl bond favors Bi⋯π arene interaction in 4 over Bi⋯halide interactions, as observed in 1 and 5. In the isostructural series [RN(CH₂C₆H₄)₂]BiX (R = CH₃OCH₂CH₂), Bi⋯oxygen interactions compensate the electron deficiency at bismuth in fluoride 8 and chloride 9, whereas the coordination sphere of bismuth is completed by a combination of Bi⋯π arene and Bi⋯halide interactions in bromide 3 and only by Bi⋯π arene interactions in iodide 10. Moreover, weak H⋯π arene and H⋯X intermolecular interactions, mainly of dispersion type, contribute to supramolecular networks in all three series of compounds.