Redox reactions of metallocenes with tungsten and molybdenum hexafluoride

Abstract

Tungsten and molybdenum hexafluoride react in acetonitrile with a series of metallocenes to give coloured salts. Oxidation of iodo-, bromo- and 1,1′-dibromo-ferrocene with both hexafluorides resulted in the formation of 1 : 1 halogenoferrocenium hexafluoro-tungstate(V) and -molybdate(V) compounds, [Fe(η-C₅H₅)(η-C₅H₄Br)][MF₆], [Fe(η-C₅H₅)(η-C₅H₄I)][MF₆] and [Fe(η-C₅H₄Br)₂][MF₆](M = W or Mo). Cobaltocene reduced MoF₆ in a two-electron step to give a 2 : 1 adduct, [Co(η-C₅H₅)₂·2MeCN]₂[MoF₆], while with WF₆ the 1 : 1 product [Co(η-C₅H₅)₂·2MeCN][WF₆] was formed. The redox reactions involving metallocenes and the hexafluorides are in agreement with the thermodynamic stabilities of their oxidation states found by electrochemical methods. The electrode potentials obtained for the metallocene hexafluorometalates consist of the two one-electron reduction steps for [MF₆]^0/–/2–(M = W or Mo) and the reversible one-electron steps for the metallocene–metallocenium couples.