The He I and He II photoelectron spectra of two
proazaphosphatranes were recorded and interpreted by
correlated
ab initio quantum chemical calculations. The first ionization
energy of the compounds investigated is among the
lowest reported hitherto for phosphorus compounds. Geometry
optimization of the ionic states of the parent
proazaphosphatrane (at the HF and MP2 levels) revealed that there are
two minima on the potential energy surface
at different P−Nax distances representing two
bond-stretch isomers. The structure with the long
P−Nax distance
(3.3 Å) is similar to that of the neutral molecule and thus has a
favorable Frank−Condon factor for the ionization
process. The other structure, with a short P−Nax
distance (2.07 Å), is as much as 1 eV lower in energy than
the
other. Due to the unfavorable Frank−Condon factor, however, the
corresponding adiabatic ionization energy
cannot be seen in the spectrum. The short P−Nax
distance in the more stable bond-stretch isomer is
characteristic
for azaphosphatranes. Its stability can thus be related to the
formation of the dative P ← N bond. The unobserved
adiabatic ionization energy should be about 1 eV lower than that of the
observed one (ca. 5.6 eV), in full agreement
with the strong basicity of proazaphosphatranes.
Aus den Isothiocyanaten (II) und Cyclohexyl‐1,3‐diamino‐propan (I) entstehen die Thioharnstoffe (III), die mit den Säurechloriden (IV) zu (V) acyliert werden.
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