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:
 * Thiazyl fluoride decomposition syntheses.webp

Reactions with electrophiles and Lewis acids
Lewis acids remove fluoride to afford thiazyl salts:
 * NSF + BF3  ->  [NS]BF4

Thiazyl fluoride functions as a ligand in [Re(CO)5NSF]+. and [M(NSF)6](2+) (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:
 * NSF + 2 H2O  ->  SO2  +  HF  +  NH3



Nucleophilic attack on thiazyl fluoride occurs at sulfur atom:.
 * NS\sF + Nu-  ->  NS\sNu  +  F-

Fluoride gives an adduct:
 * NS\sF + F-  ->  NSF2-

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 multiple bonding:


 * NSF-trimerization.webp

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.


 * NSF-pi-rxn3.webp

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


 * NSF Resonance-Lewis Structure2.webp

The NSF molecule has 18 total valence electrons and is isoelectronic to sulfur dioxide. Thiazyl fluoride adopts Cs-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 bond by 0.11 Å and a decrease in the $$\measuredangle$$NSF by 15.3$$^\circ$$.