Frank Neumann

Vibrational spectra of the tetramethylpnikogenonium ions

Abstract The tetramethylpnikogenonium ions (CH 3 ) 4 X + (X = N, P, As, Sb) have been studied by infrared and Raman spectroscopy. Additionally, their structures and vibrational frequencies were ab initio calculated at the HF/6-31+G* and for (CH 3 ) 4 Sb + at the HF/6-31+G*/LANL2DZ level of theory. For the tetrahedral cations an assignment of the vibrational frequencies is discussed on the basis of a comparison of calculated and measured frequencies.

Struktur und Eigenschaften von Methyltrifluorphosphoran CH3PF3H

Methyldichlorphosphan reagiert mit drei aquivalenten HF zu Methyltrifluorphosphoran, das durch Massen-, NMR- und Schwingungsspektroskopie charakterisiert wird. Aus einer ab initio Rechnung (HF/6-31+G*) ergibt sich ein verzerrt trigonal bipyramidaler Aufbau fur CH3PF3H. Die Methylgruppe (r P—C = 180.2 pm), das Wasserstoffatom (r P—H = 137.1 pm) und ein Fluoratom (r P—Faq = 155.8 pm) nehmen aquatoriale Positionen ein. Der P—Fax-Abstand betragt 163.4 pm. Die Lewis-amphoteren Eigenschaften der Verbindung wurden durch Reaktionen mit CsF, [(CH3)4]NF und AsF5 belegt. Structure and Properties of Methyltrifluorophosphorane CH3PHF33 Methyldichlorophosphane reacts with three equivalents of HF under formation of Methyltrifluorophosphorane, which is characterized by mass, NMR, and vibrational spectroscopy. The ab intio calculation (HF/6-31+G*) yields a distorted trigonal bipyramidal structure for CH3PF3H. The methyl group (r P—C = 180.2 pm), the hydrogen (r P—H = 137.1 pm) and one fluorine atom (r P—Feq = 155.8 pm) are located at equatorial positions. The P—Fax-distance is 163.4 pm. The Lewis-amphoteric properties are shown by reactions with CsF, [(CH3)4]NF and AsF5.

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. Graphical Abstract Reactivity of Tetramethylphosphonium Fluoride in Acetonitrile Solutions

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.