Formation of difluorosulfane complexes of the third row transition metals by sulfur-to-metal fluorine migration in trifluorosulfane metal complexes: The anomaly of trifluorosulfane iridium tricarbonyl

The stability of the experimentally known complex (Et₃P)₂Ir(CO)(Cl)(F)(SF₃) of the third row transition metal iridium suggests that SF₃ complexes of the third row transition metals might be viable species in contrast to the SF₃ complexes of the first row transition metals previously studied by theoretical methods. However, the metal complexes [M](SF₃) ([M] = Ta(CO)₅, Re(CO)₄, CpW(CO)₂, CpOs(CO), and CpPt) containing three-electron donor tetrahedral SF₃ ligands are thermodynamically disfavored relative to the isomeric [M](SF₂)(F) derivatives with predicted energy differences ranging from -19 to -44 kcal/mol. The one exception is an Ir(SF₃)(CO)₃ isomer containing a one-electron donor pseudo-square-pyramidal SF₃ ligand having essentially the same energy as the lowest energy Ir(SF₂)(F)(CO)₃ isomer. This, as well as the stability of the known (Et₃P)₂Ir(CO)(Cl)(F)(SF₃), suggests that metal complexes containing one-electron donor pseudo-square-pyramidal SF₃ ligands might be viable synthetic objectives in contrast to those containing three-electron donor tetrahedral SF₃ ligands. The [M](SF₂)(F) derivatives formed by sulfur-to-metal fluorine migration from isomeric [M](SF₃) complexes are predicted to be viable toward SF₂ dissociation to give the corresponding [M](F) derivatives. This suggests the possibility of synthesizing metal complexes of the difluorosulfane (SF₂) ligand via the corresponding metal trifluorosulfane complexes with the SF₃⁺ cation as the ultimate source of the SF₂ ligand. Such a synthetic approach bypasses the need for the very unstable SF₂ as a synthetic reagent.