Tuning the Anomeric Effect in Sulfamide with Superacids.

This study shows that the anomeric effect (negative hyperconjugation) that arises in sulfamide, as a result of the relatively short S−N bonds, can be tuned by the utilization of superacidic media. Sulfamide was reacted in binary superacidic systems XF/MF5 (M=As, Sb; X=H, D) and HF/BF3. The colorless salts formed, [X2NSO2NX3]+[MF6]− and [H2NSO2NH3]+[BF4]− were characterized by low‐temperature vibrational spectroscopy. In the case of [H2NSO2NH3]+[BF4]−, a single crystal X‐ray diffraction study was performed. The salt crystallizes in the monoclinic space group P21/c with four formula units per unit cell. An exclusive N,N′‐diprotonation was observed in the superacidic system HF/SbF5 when using several equivalents of the Lewis acid. Low‐temperature vibrational spectra as well as a single‐crystal X‐ray structure of [H3NSO2NH3]2+2 [SbF6]−⋅2 HF are reported. The salt crystallizes in the orthorhombic space group Pna21 with four formula units per unit cell. Upon mono‐ or diprotonation of sulfamide, remarkable structural changes of the sulfur–nitrogen bond lengths were observed. Herein, these changes are discussed together with quantum chemical calculations. Structural effects: Sulfamide undergoes remarkable structural changes upon protonation. Dependent on the amount of the Lewis acids AsF5 or SbF5 with respect to sulfamide, salts containing [H2NSO2NH3]+ (I) and [H3NSO2NH3]2+ (II) are isolable. The structural changes are discussed in the context of the anomeric effect. [ABSTRACT FROM AUTHOR]