Synthesis and Reactivity of [SF₃]⁺ Adducts with Organic Bases

The 1:1 adduct of [SF₃]⁺ with pyridine was obtained from the reaction of SF₄ with [(CH₃)₃Si(NC₅H₅)][O₃SCF₃] ([(CH₃)₃Si(py)][OTf]) as the [SF₃(py)][OTf] salt in near quantitative yields. The analogous reaction of SF₄ with [(CH₃)₃Si(4-NC₅H₅N(CH₃)₂)][OTf] ([(CH₃)₃Si(dmap)][OTf]) results in the formation of a small amount of [SF₃(dmap)][OTf], which was found to undergo facile dismutation to [SF₂(dmap)₂][OTf]₂ and SF₄ as the major products of the reaction. NMR spectroscopic data suggest that [SF₃(dmap)]⁺ adopts a seesaw structure with DMAP in the equatorial position, which is in contrast to the axial position of pyridine in [SF₃(py)]⁺. Quantum chemical calculations show that in the gas-phase the axial isomer of [SF₃(py)]⁺ is the more stable configuration by 28 kJ mol^-1, whereas the axial and equatorial isomers of [SF₃(dmap)]⁺ were predicted to be essentially isoenergetic with <2 kJ mol^-1 difference between the two isomers. The reaction of [SF₃][SbF₆] with DMAP allowed for the isolation of [SF₂(dmap)₂][SbF₆]₂ without any evidence of the monocation. In CH₃CN solutions, [SF₂(dmap)₂]²⁺ was found to undergo further ligand scrambling leading to the precipitation of [SF(dmap)₄]³⁺ salts. Attempts to form a 1:1 adduct between [SF₃]⁺ and OPPh₃ result instead in the deoxofluorination of OPPh₃ forming [FPPh₃]⁺ salts.