Fluorination of vanadates with organic fluorinating agents

Abstract

The organic fluorinating agents [bis(2-methoxyethyl)amino]sulfur trifluoride (Deoxo-fluor®), diethylaminosulfur trifluoride (DAST), and N-fluorobenzenesulfonimide (NFSI) were used to inspect the efficiency of fluorination of monovanadate, H_xVO₄^(3−x)− (V₁), and decavanadate, H_xV₁₀O₂₈^(6−x)− (V₁₀), in solution by ⁵¹V NMR spectroscopy. It was observed that either VOF₄⁻ or VO₂F₂⁻ can be generated in acetonitrile solutions at room temperature after one hour selectively for H_xVO₄^(3−x)−, while H_xV₁₀O₂₈^(6−x)− is more sensitive towards reduction and only NFSI can be used to generate VOF₄⁻. The differences in reactivity can be attributed to the electrophilicity of fluorine in Deoxo-fluor® and DAST, and its nucleophilicity in NFSI. Tetrabutylammonium fluoride, triethylamine trifluoride, and hydrogen fluoride–pyridine adduct were also used under the same conditions for comparison of the efficiency and selectivity of fluorination. It was observed that only HF.pyridine provided a complete transformation of V₁ and V₁₀ into VOF₄⁻. The pilot experiments introduced in this work are the first example of fluorination of polyoxometalates with organic fluorination agents and other less commonly used fluorides with organic cations and show their great potential in the synthesis of polyoxometalates with fluorido ligand.