Sulfur difluoride and sulfur monofluoride as ligands in iron carbonyl chemistry

Abstract

Density functional theory predicts a binuclear Fe₂(μ-SF₂)₂(CO)₈ octacarbonyl structure with two bridging SF₂ groups and a long Fe⋯Fe distance of ∼3.5 Å indicating a lack of a direct iron–iron bond. In addition, three Fe₂(μ-SF₂)(SF₂)(CO)₇ stereoisomers of similar energies are found with one bridging SF₂ group and one terminal SF₂ group and an even longer Fe⋯Fe distance of ∼3.9 Å likewise indicating a lack of a direct iron–iron bond. In contrast to the binuclear Fe₂(SF₂)₂(CO)_n (n = 8, 7) derivatives, the mononuclear Fe(SF₂)(CO)_n (n = 4, 3) are disfavored by ∼10 kcal mol⁻¹ for n = 4 to ∼30 kcal mol⁻¹ for n = 3, respectively, with respect to fluorine shift from sulfur to iron to give the corresponding Fe(SF)(F)(CO)_n derivatives. The SF ligands in the tetracarbonyls Fe(SF)(F)(CO)₄ are one-electron donor ligands with Fe–S distances of ∼2.3 Å. However, the SF ligands in the tricarbonyls Fe(SF)(F)(CO)₃ are three-electron donor ligands with significantly shorter FeS distances of ∼2.1 Å.