An original approach involving a coupling in the gas phase between flash vacuum thermolysis (FVT) and UV-photoelectron spectroscopy (UV-PES) allowed the transient terminal electrophilic phosphanylidene complex [MeP=W(CO)5] to be characterized; this is the first direct observation of this P–Me derivative. This approach also permitted the electronic structure of [PhP=W(CO)5] to be revisited and confirmed the results obtained with the methylated analogues. In contrast, [p-NC–C6H4P=W(CO)5] proved to be too reactive to be detected under our experimental conditions. These [RP=W(CO)5] phosphanylidene complexes (R: Me, Ph) were identified by their ionization potentials, which are real “fingerprints”. These experimental data, supported by density functional calculations, give an overall electronic cartography of these transient species. For generation in the gas phase of these phosphanylidene complexes, the thermal degradation of two kinds of precursors were investigated. The joint experimental/theoretical approach allowed us to conclude that phosphanorbornadiene complexes are more suitable precursors than phosphirane complexes.