Isolation and crystal and molecular structures of [(C5H2Br3)2Fe], [(C5HBr4)2Fe] and [(C5Br5)(C5Br4HgBr)Fe]

Abstract

The reaction of [(C₅H₃Br₂)₂Fe] with lithium tetramethylpiperidinide (LiTMP) in a 1:10 molar ratio in tetrahydrofuran yields, after quenching with C₂H₂Br₄, a mixture of the polybromoferrocenes [C₁₀H_10-nBr_nFe] with n = 4-9, from which single crystals of bis(1,2,3-tribromocyclopentadienyl)iron(II), [Fe(C₅H₂Br₃)₂], and bis(1,2,3,4-tetrabromocyclopentadienyl)iron(II), [Fe(C₅HBr₄)₂Fe], were obtained by a combination of chromatography and fractional crystallization. Treatment of `[C₁₀(HgOAc)₁₀Fe]' with KBr₃ yields a mixture of polybromoferrocenes [C₁₀H_10-nBr_nFe] with n = 8-10 and bromomercurioferrocenes [C₁₀H_9-nBr_n(HgBr)Fe] with n = 7-9, from which single crystals of (1-bromomercurio-2,3,4,5-tetrabromocyclopentadienyl)(1,2,3,4,5-pentabromocyclopentadienyl)iron(II), [FeHgBr(C₅Br₄)(C₅Br₅)], were obtained by fractional crystallization. The crystal structures of all the compounds show Br...Br, Br...H and sometimes Br...Cp...π (Cp is a ring centroid) interactions, as well as π-π interactions. The findings are supported by Hirshfeld analyses.

Keywords: Hirshfeld analysis; bromoferrocene; crystal structure; halogen bonding; noncovalent interactions.