Taming a Blue Gas—Structure and Chemistry of Hexafluorothioacetone

ABSTRACT Hexafluorothioacetone ( 1 ), a blue gas at r.t. and unusually prone to dimerization, was synthesized and characterized by single‑crystal x‑ray diffraction, NMR spectroscopy, and density functional theory (DFT) calculations. The C═S bond lengths in 1 were determined to be 1.583–1.595 Å, representing the shortest C═S bond lengths reported for a non‐cumulene system. DFT calculations indicate an only mildly polar covalent C═S bond. Furthermore, due to the strongly electron withdrawing CF 3 groups, the polarity of the C═S bond is reversed to C δ– ═S δ+ , running contrary to their electronegativities. The 13 C NMR spectrum of neat 1 collected at 193 K shows resonances at 205.4 ppm ( 2 J CF = 37.7 Hz) and 116.7 ppm ( 1 J CF = 278.7 Hz), with the thiocarbonyl resonance shifted unusually far up‐field, further underscoring the inverted polarity of the C═S bond. Nickel complexes with 1 as side‐on ligand (η 2 ) and ancillary ligands (COD, pyridine, TMEDA) were obtained, in which the nickel atom adopts a pseudo square‑planar geometry. The C–S bond lengths in these complexes (1.735–1.762 Å) lie between typical single (1.78 Å) and double (1.61 Å) bonds.