Charge-compensated nido-carborane derivatives in the synthesis of iron(ii) bis(dicarbollide) complexes

Abstract

A series of stable iron(II) bis(dicarbollide) derivatives [8,8′-(RNHC(Et)HN)₂-3,3′-Fe(1,2-C₂B₉H₁₀)₂] (R = Pr, R = Ph, (CH₂)₂OH, (CH₂)₃OH, (CH₂)₂NMe₂) was prepared starting from FeCl₂ or [FeCl₂(dppe)] and the corresponding nido-carboranyl amidines [10-RNHC(Et)HN-7,8-C₂B₉H₁₁]. In a similar way, the reactions of the oxonium derivatives of nido-carborane with FeCl₂ in tetrahydrofuran in the presence of t-BuOK lead to the corresponding stable oxonium derivatives iron(II) bis(dicarbollide) [8,8′-(RR′O)₂-3,3′-Fe(1,2-C₂B₉H₁₀)₂] (RR′ = (CH₂)₄, (CH₂)₂O(CH₂)₂, (CH₂)₅; R = R′ = Et), which can be alternatively prepared by the reaction of the parent iron(II) bis(dicarbollide) with tetrahydrofuran or 1,4-dioxane in the presence of Me₂SO₄. The cyclic voltammetry studies of the synthesized iron(II) bis(dicarbollide) derivatives revealed that the introduction of amidinium and oxonium substituents leads to a significant increase in the Fe²⁺/Fe³⁺ redox potential relative to the parent iron(II) bis(dicarbollide). The redox potentials of the oxonium derivatives are close to the redox potential of ferrocene and somewhat lower than redox potentials of sulfonium and phosphonium derivatives of iron(II) bis(dicarbollide).