Synthesis of P-chlorophosphaethene and N-chloromethanimine: Estimation of Cl substitution on the electronic structure of heteroatomic double bonds
Résumé
Comparison between the electronic structure of N-chloroaldimines and P-chlorophosphaethene has been achieved by photoelectron spectroscopy. Whereas N-chloroaldimines have been synthetized in the gas phase by a new "one-line" reaction starting from α-cyanoamines (vacuum gas-solid reaction, VGSR), P-chlorophosphaethene has been generated by flash vacuum thermolysis (FVT) of dichloromethylphosphine. Chlorine substitution at the heteroatom destabilizes the double bond to a much greater extent for aldimines than for phosphaethene, thus reflecting a greater interaction between chlorine and πC=N than between chlorine and πC=P and a more diffuse character of the πC=P bond than the πC=N bond. For both series the heteroatom substitution does not modify the ionization energy of the heteroatom lone pair. This observation is evidence for a counterbalance between a stabilizing inductive effect of chlorine and a destabilizing interaction between the lone pairs. The discrepancy between the experimental results and the theoretical evaluation of the ionization potential is again pointed out for compounds bearing third-row atoms involved in double bonds. © 1989 American Chemical Society.