Stabilization of [WF₅]⁺ by Bidentate N-Donor Ligands

Transition-metal hexafluorides do not exhibit fluoride-ion donor properties in the absence of donor ligands. We report the first synthesis of donor-stabilized [MF₅]⁺ derived from a transition-metal hexafluoride via fluoride-ion abstraction using WF₆(L) (L=2,2′-bipy, 1,10-phen) and SbF₅(OSO) in SO₂. The [WF₅(L)][Sb₂F₁₁] salts and [WF₅(1,10-phen)][SbF₆]⋅SO₂ have been characterized by X-ray crystallography, Raman spectroscopy, and multinuclear NMR spectroscopy. The reaction of WF₆(2,2′-bipy) with an equimolar amount of SbF₅(OSO) reveals an equilibrium between [WF₅(2,2′-bipy)]⁺ and the [WF₄(2,2′-bipy)₂]²⁺ dication, as determined by ¹⁹F NMR spectroscopy. The geometries of the cations in the solid state are reproduced by gas-phase geometry optimizations (DFT-B3LYP), and NBO analyses reveal that the positive charges of the cations are stabilized primarily by compensatory σ-electron donation from the N-donor ligands.