Electrochemical and Theoretical Studies of the Impact of the Chelating Ligand on the Reactivity of [Fe-2(CO)(4)(kappa(2)-LL)(mu-pdt)](+) Complexes with Different Substrates (LL = I-Me-CH2-I-Me, dppe; I-Me=1-Methylimidazol-2-ylidene)

The reactivity of [Fe-2(CO)(4)(kappa(2)-LL)(mu-pdt)](+) complexes (pdt = S(CH2)(3)S, propanedithiolate) with different substrates L' (L' = CO, MeCN, P(OMe)(3)) was investigated electrochemically in order to assess the influence of the chelating ligand kappa(2)-LL (LL = I-Me-CH2-I-Me (1(+)), dppe (2(+)); I-Me = 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 [Fe-2(CO)(4)(mu-CO)(kappa(2)-dppe)(mu-pdt)](+) (2-CO+) was clearly observed by cyclic voltammetry, whereas [Fe-2(CO)(4)(mu-CO)(kappa(2)-I-Me-CH2-I-Me)(mu-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 [Fe-2(CO)(4)(kappa(2)-I-Me-CH2-I-Me)(mu-pdt)](+) (1(+)) with P(OMe)(3) produces the disubstituted dication [Fe-2(CO)(2){P(OMe)3}(2)(kappa(2)-I-Me-CH2-I-Me)(mu-CO)(mu-pdt)](2+) (4(2+)) 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 kappa(2)-dppe cations.