Ethenylphosphine. Synthesis by Flash-Vacuum Thermolysis and Characterization by Photoelectron Spectroscopy

Article abstract of DOI:10.1021/ja00217a006

Ethenylphosphine and prop-1-en-2-ylphosphine, obtained by flash-vacuum thermolysis of the corresponding Diels-Alder adducts, have been characterized by their photoelectron spectra.In both cases, the broad shape of the first two bands respectively at 9.65 and 10.85 eV for ethenylphosphine and at 9.50 and 10.3 eV for prop-1-en-2-ylphosphine can only be accounted for if we assume a free-rotating P-C bond.This conclusion was inferred from a complete theoretical study of the rotation process of the PH2 group around the P-C bond.Two privileged forms were found: a syn form (Φ = o, the lone pair of the phosphorus eclipsing the P-C bond) and a gauche form 3.5 kJ*mol^-1 less stable (Φ = 127^o), separated by low rotation barriers (8.19 and 10.74 kJ*mol^-1).Evaluation of the accurate ionization potentials according to a configuration interaction formalism has been achieved for ethenylphosphine in different conformations.The results of these calculations clearly indicate that during the rotation process the energy of the first two ionic states extends over a 0.4 eV interval.