23.07.2026 Taming a Blue Gas

Hexafluorothioacetone (F₂C)₂C=S is a reactive blue gas that dimerizes so readily its crystal structure required non stop liquid nitrogen temperature while handling. The result: the shortest C=S bond reported for a non-cumulene thioketone. The CF₃ groups flip the bond's polarity, reversing the usual C=S dipole - confirmed by an unusually upfield ¹³C NMR shift for the thiocarbonyl carbon, far outside the typical range. η²-coordination to Ni(0) with various ancillary ligands (COD, pyridine, TMEDA) gives C–S bonds between single- and double-bond character, pointing to a metallacyclopropane-skewed Dewar–Chatt–Duncanson description - more pronounced with weaker π-acceptor ligands.

The whole story is now published in Angew. Chem. Int. Ed. (doi:10.1002/anie.1044664).