A Molecular Precursor to Phosphaethyne and Its Application in Synthesis of the Aromatic 1,2,3,4-Phosphatriazolate Anion

Dibenzo-7-phosphanorbornadiene
Ph3PC­(H)­PA (1, A = C14H10, anthracene) is reported here as
a molecular precursor to phosphaethyne (HCP), produced together
with anthracene and triphenylphosphine. HCP generated by thermolysis
of 1 has been observed by molecular beam mass spectrometry,
laser-induced fluorescence, microwave spectroscopy, and nuclear magnetic
resonance (NMR) spectroscopy. In toluene, fragmentation of 1 has been found to proceed with activation parameters of ΔH⧧ = 25.5 kcal/mol and ΔS⧧ = −2.43 eu and is accompanied
by formation of an orange insoluble precipitate. Results from computational
studies of the mechanism of HCP generation are in good agreement with
experimental data. This high-temperature method of HCP generation
has pointed to new reaction chemistry with azide anion to produce
the 1,2,3,4-phosphatriazolate anion, HCPN3–, for which structural data have been obtained in a single-crystal
X-ray diffraction study. Negative-ion photoelectron spectroscopy has
shown the adiabatic detachment energy for this anion to be 3.555(10)
eV. The aromaticity of HCPN3– has been
assessed using nucleus-independent chemical shift, quantum theory
of atoms in molecules, and natural bond orbital methods.