Synthesis and Reactivity of Thioether-Dithiolate-Bridged Multi-iron Complexes

The
novel thioether-dithiolate-bridged diiron complex [Cp*Fe­(μ-1κ3SSS′:2κ2SS-tpdt)­FeCp*] (1, Cp*
= η5-C5Me5; tpdt = S­(CH2CH2S−)2) has been
prepared by the reaction of [Cp*FeCl]2 with Li2(tpdt) in THF. Given the thermodynamic instability of 1, a one-electron oxidation was performed with Fc·PF6 (Fc = ferrocene) affording 1­[PF6]. Treatment of 1­[PF6] with CO or tBuNC
in CH2Cl2 gave complexes [Cp*Fe­(μ-1κ3SSS′:2κ2SS-tpdt)­{Cp*Fe­(η1-CO)}]­[PF6] (2­[PF6]) and [Cp*Fe­(μ-1κ3SSS′:2κ2SS-tpdt)­{Cp*Fe­(η1-tBuNC)}]­[PF6] (3­[PF6]). In addition, complex 1­[PF6] can be further oxidized into [Cp*Fe­(μ-1κ3SSS′:2κ2SS-tpdt)­FeCp*]­[PF6]2 (1­[PF6]2) by Fc·PF6 in THF, while in the presence
of MeCN resulting in the formation of complex [Cp*Fe­(μ-1κ3SSS′:2κ2SS-tpdt)­{Cp*Fe­(η1-MeCN)}]­[PF6]2 (4­[PF6]2). When the
solution of complex 1 in THF was warmed to room temperature,
thioether-dithiolate-bridged trinuclear iron complex [Cp*Fe­(μ-1κ3SSS′:2κ2SS-tpdt)­Fe­(μ-2κ2SS:3κ3SSS′-tpdt)­FeCp*] (5), which can be oxidized
into complex [Cp*Fe­(μ-1κ3SSS′:2κ2SS-tpdt)­Fe­(μ-2κ2SS:3κ3SSS′-tpdt)­FeCp*]­[PF6]2 (5­[PF6]2) with Fc·PF6, was
obtained accompanied by byproduct Cp*2Fe. Complex 5 is sensitive to air and upon exposure to air in THF gave
monoiron complex [Cp*Fe­(tpdt)] (6) in moderate yield.
Complex 6 is a good metallothiolato precursor for synthesis
of homo- and heterobimetallic or trimetallic complexes. The binuclear
complex [Cp*Fe­(μ-1κ3SSS′:2κ2SS-tpdt)­FeCl2] (7) can be prepared by the reaction of complex 6 with anhydrous FeCl2 in CH2Cl2. Complex 5­[PF6]2 can also be obtained by the reaction
of complex 6 with FeCl2 or complex 7 in the presence of NH4·PF6. These complexes
have been spectroscopically and crystallographically characterized.