Preparation and properties of dimethyltetrafluorophosphate.

Dimethyltrifluorophosphorane reacts with strong fluoride donors, such as CsF, Me(4)NF, and Me(4)PF, under formation of dimethyltetrafluorophosphates. The salts were characterized by infrared and Raman spectroscopy and in acetonitrile solutions by NMR spectroscopy. The experimental results show that only the trans isomer is formed. Theoretical calculations (B3LYP/6-31+G* and RHF/6-31+G*) of the trans and cis isomer yielded a difference of the Gibbs free energy of 29.4 kJ/mol (B3LPY/6-31+G*). The Me(4)N(+)[Me(2)PF(4)](-) crystallizes in the orthorhombic space group Pnma with four formula units per unit cell and dimensions of a = 1303.5(3), b = 799.8(2), and c = 1023.8(4) pm. The phosphorus atom has an octahedral environment with P-C distances of 183.4(3) pm and P-F bond lengths in the range between 166.1(1) and 168.2(1) pm. In the crystal packing, anions and cations are linked via weak fluorine hydrogen contacts forming a three-dimensional network.