Reactivity of Tetramethylphosphonium Fluoride in Acetonitrile Solutions

Anhydrous tetramethylphosphonium fluoride dissolved in acetonitrile reacts slowly with the solvent under formation of (E)-2-amino-1-cyano-propene which was characterized by infrared and NMR spectroscopy. An attempted preparation of [Me3PF3]− by addition of Me3PF2 to Me4PF/acetonitrile solutions has shown that the desired reaction does not occur, but prolonged reaction times and small acetonitrile concentrations lead to the formation of the iminophosphorane Me3P=NC(Me)=CH2 and [Me4P]+HF2−. Me3P=NC(Me)=CH2 was characterized by infrared spectroscopy and a single-crystal structure determination. N-(2-propenyl)trimethyliminophosphorane crystallizes in the monoclinic space group P21/c with a = 1006.8(2), b = 1523.5(3), c =1180.3(2) pm, β = 111.72(6)◦ and Z = 8. The two independent molecules per unit cell have nearly planar P=NC(C)=C skeletons with torsion angles P–N–C–C of 5.9(3)◦ and 7.1(4)◦ and an average P=N distance of 158.1(2) pm. The general ability of Me4PF as a fluoride donor was proven by the reaction with SO2 which results in the formation of [Me4P]+SO2F−. The colorless salt was characterized by infrared, Raman, and NMR spectroscopy.