Thiazyl fluoride

Thiazyl fluoride, NSF, is a colourless, pungent gas at room temperature and condenses to a pale yellow liquid at 0.4 °C. Along with thiazyl trifluoride, NSF₃, it is an important precursor to sulfur-nitrogen-fluorine compounds. It is notable for its extreme hygroscopicity.

Synthesis

Thiazyl fluoride can be synthesized by various methods, such as fluorination of tetrasulfur tetranitride with silver(II) fluoride or mercuric fluoride. It can be purified by vacuum distillation. However, because this synthetic pathway yields numerous side-products, an alternative approach is the reaction of imino(triphenyl)phosphines with sulfur tetrafluoride by cleavage of the bond to form sulfur difluoride imides and triphenyldifluorophosphorane. These products readily decompose yielding thiazyl fluoride.

For synthesis on a preparative scale, the decomposition of compounds already containing the moiety is commonly used:

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Reactivity

Reactions with electrophiles and Lewis acids

Lewis acids remove fluoride to afford thiazyl salts:

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Thiazyl fluoride functions as a ligand in Template:Chem2. and Template:Chem2 (M = Co, Ni). In all of its complexes, NSF is bound to the metal center through nitrogen.

Reactions with nucleophiles

Thiazyl fluoride reacts violently with water:

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2D contour plot of the electron density using the Laplacian function of thiazyl fluoride.

Nucleophilic attack on thiazyl fluoride occurs at sulfur atom:.

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Fluoride gives an adduct:

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The halogen derivatives XNSF₂ (X = F, Cl, Br, I) can be synthesized from reacting Hg(NSF)₂ with X₂; whereby, ClNSF₂ is the most stable compound observed in this series.

Oligomerization and cycloaddition

At room temperature, thiazyl fluoride undergoes cyclic trimerization via the $\mathrm{N}-\mathrm{S}$ multiple bonding:

1,3,5-trifluoro-1${\lambda }^4$,3${\lambda }^4$,5${\lambda }^4$,2,4,6-trithiatriazine is the yielded cyclic trimer, where each sulfur atom remains tetravalent.

Thiazyl fluoride also reacts via exothermic cycloaddition in the presence of dienes.

Structure and bonding

Frontier molecular orbitals of thiazyl fluoride calculated at the r2SCAN-3c level of theory

The N−S bond length is 1.448 Å, which is short, indicating multiple bonding, and can be represented by the following resonance structures:

The NSF molecule has 18 total valence electrons and is isoelectronic to sulfur dioxide. Thiazyl fluoride adopts C_s-symmetry and has been shown by isotopic substitution to be bent in the ground state. A combination of rotational analysis with Franck-Condon calculations has been applied to study the electronic excitation from the A''$-$A' states, which results in the elongation of the nitrogen-sulfur bond by 0.11 Å and a decrease in the $\measuredangle$NSF by 15.3${\circ }^{}$.