Evidence for “Halogen‐Dance” and Ring‐Exchange Reactions in Chloro‐methylthio‐ferrocenes

• Published in: European journal of organic chemistry Vol. 2020; no. 42; pp. 6576 - 6587
• Main Authors: Blockhaus, Tobias, Bernhartzeder, Stefanie, Kempinger, Werner, Klein‐Heßling, Christian, Weigand, Stefan, Sünkel, Karlheinz
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 15.11.2020; Wiley Subscription Services, Inc
• Subjects: Chemistry; Chemistry, Organic; Chloroaromatics; Chloroferrocenes; Crystal structure; Cyclopentadienyl ring exchange; Dance; Exchanging; Ferrocenes; Ferrocenyl thioethers; Halogen dance; Molecular structure; Physical Sciences; Science & Technology; Halogen dance; PERHALOGENATED CYCLOPENTADIENES; COMPLEXES; CHEMISTRY; Chloroferrocenes; Cyclopentadienyl ring exchange; Ferrocenyl thioethers; Crystal structure
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.202001032

The pentachloroferrocenes [C5Cl5]Fe[C5H4X] (X = H, Br, SMe) react with LiTMP and MeSSMe to form mixtures of compounds, that contain besides the expected products of deprotonation also one or more complexes with a [C5Cl4(SMe)] ligand. This latter observation makes the otherwise rarely observed occurrence of “halogen dance reactions” in chloroaromatics very probable. 1,2,3‐Trichloroferrocene yields with BuLi and MeSSMe products of both halogen‐metal‐exchange and of deprotonation. Additionally, in all examined systems, the observation of some highly‐substituted complexes with eight or more substituents hints to the involvement of cyclopentadienyl exchange reactions, which has also rarely been observed under such mild conditions. The molecular structures of [C5Cl4(SMe)]Fe[C5H3BrX] (X = SMe or SOMe), [C5Cl4(SMe)]Fe[C5H2Cl(SMe)2], [C5Cl2(SMe)3]2Fe, and [C5HCl3(SMe)]2Fe have been determined by X‐ray diffraction. Deprotonation of pentachloroferrocenes [C5Cl5]Fe[C5H4X] (X = H, Br, SMe) and quench with MeSSMe produces complex product mixtures, which include compounds with [C5Cl4(SMe)] ligands or compounds which contained six or more chlorine atoms. The occurrence of such products can only be explained by halogen‐dance and/or cyclopentadienyl ring exchange reactions. Herein, some of the key compounds could be characterized by X‐ray diffraction.