Interaction Modes Between SF₄ and Ketones; Study of Intermediates in Deoxofluorination Reactions

Interactions between ketones and SF₄ are studied for the simplest ketone, acetone, and the bulky polycyclic 2-adamantanone. Acetone forms the 1 : 2 adduct SF₄  ⋅ [O=C(CH₃ )₂ ]_2, as well as the dimeric 1 : 1 adducts [SF₄  ⋅ O=C(CH₃ )₂ ]₂ as identified by low-temperature Raman spectroscopy and, for the latter, X-ray crystallography. In both adducts, SF₄ acts as a double chalcogen-bond donor to two keto groups. In contrast 2-adamantanone does not form an isolable solid adduct with SF₄ ; in the presence of HF, however, it forms SF₄  ⋅ O=C₁₀ H₁₄ O ⋅ HF, which comprises chains with weak S-O and S-FH chalcogen bonds in the crystal structure. Sulfur tetrafluoride in this compound is readily lost at -85 °C, leading to the isolation of C₁₀ H₁₄ O ⋅ HF at low temperature. Density functional theory (DFT) calculations aid in vibrational assignments and serve to describe the interactions of the keto group with SF₄ and HF, as well as interactions between SF₄ with HF. It is found that separate and combined CO-HF and CO-SF₄ chalcogen bonds do not polarize the C=O group to any significant degree.