Electrochemical and Theoretical Studies of the Impact of the Chelating Ligand on the Reactivity of [Fe<sub>2</sub>(CO)<sub>4</sub>(κ<sup>2</sup>-LL)(μ-pdt)]<sup>+</sup> Complexes with Different Substrates (LL = I<sub>Me</sub>-CH<sub>2</sub>-I<sub>Me</sub>, dppe; I<sub>Me</sub> = 1-Methylimidazol-2-ylidene)
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The reactivity of [Fe2(CO)4(κ2-LL)(μ-pdt)]+ complexes (pdt = S(CH2)3S, propanedithiolate) with different substrates L′ (L′ = CO, MeCN, P(OMe)3) was investigated electrochemically in order to assess the influence of the chelating ligand κ2-LL (LL = IMe-CH2-IMe (1+), dppe (2+); IMe = 1-methylimidazol-2-ylidene). This latter ligand is effectively shown to affect the reactivity of the cations in different ways: when L′ = CO, the adduct [Fe2(CO)4(μ-CO)(κ2-dppe)(μ-pdt)]+ (2-CO+) was clearly observed by cyclic voltammetry, whereas [Fe2(CO)4(μ-CO)(κ2-IMe-CH2-IMe)(μ-pdt)]+ (1-CO+) was not detected, although DFT calculations show that the energies of the products and the activation barriers to their formation are similar. When L′ = MeCN, the adducts X-MeCN+ with X = 1, 2 are both observed, but the formation is easier when LL = dppe. Finally, the reaction of [Fe2(CO)4(κ2-IMe-CH2-IMe)(μ-pdt)]+ (1+) with P(OMe)3 produces the disubstituted dication [Fe2(CO)2{P(OMe)3}2(κ2-IMe-CH2-IMe)(μ-CO)(μ-pdt)]2+ (42+) via a disproportionation reaction, while previous studies demonstrated that monocationic derivatives were obtained when LL = dppe. Complex 4[PF6]2 was fully characterized, and its X-ray crystal structure confirms the presence of a carbonyl ligand in a bridging position, which did not exist in the related P(OMe)3-substituted κ2-dppe cations.
