A tetraimido sulfuric acid

A tetraimido sulfuric acid
03 March 2021 - Chemical Zoo

tetraimido sulfuric acid Jung 2021.PNGThe Stalke group (University of Göttingen) has recently reported the synthesis and isolation of a tetraimido sulfuric acid (Jung et al. DOI). Where regular sulfuric acid has a central sulfur atom, two hydroxyl groups and two oxo groups, in the new compound the substituents are two formal amino NHtBu groups and two formal imido NtBu groups. Both compounds are therefore structurally related and because the arrangement of valence electrons is unchanged you can regard the compounds as isoelectronic.

The starting compound for the 2021 synthesis has been sitting on a shelf in the Stalke lab since 1998 (DOI). The synthetic route can be sourced back to sulfur chloride which in a well-known reaction reacts with tert-butylamine to the sulfur diimide di-t-butyl-sulfurdiimide. Addition of lithium tert-butylamide followed by oxidation with bromine gives access to an compound S(NtBu)3 and another round with the lithium amide gives butterfly compound dilithium-N,N',N,N'-tetrakis(tert-butyl)tetra-imidosulfate.

In the new work this compound was stirred in THF for 2 minutes with tert-butylammonium chloride to yield the tetraimido sulfuric acid compound. Sometimes developing new chemistry can be that simple. The new compound is stable if kept below 35 degrees below zero otherwise it's fate is conversion back to S(NtBu)3 which is an equivalent of sulfur trioxide.

Structural analysis: from the crystal structure the bond lengths of the amido S-N bonds and the imido bonds are not surprising. From QTAIM computations, the shorter imido bonds are also found to be more polarized towards nitrogen. It is tempting to draw the imido bond as a double bond e.g. S=N but, surprise, according to the analysis, it is a polar single bond just as the amido bond.