Taming a Blue Gas-Structure and Chemistry of Hexafluorothioacetone

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 CF₃ groups, the polarity of the C═S bond is reversed to C^δ-═S^δ+, running contrary to their electronegativities. The ¹³C NMR spectrum of neat 1 collected at 193 K shows resonances at 205.4 ppm (²J_CF = 37.7 Hz) and 116.7 ppm (¹J_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 (η²) 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.