A theoretical study of the substituent effects on the P-X (X = H, F, Cl) bond dissociation energies in para- and meta-substituted aromatic phosphines

The P-X (X = H, F, and Cl) bond dissociation energies (BDEs) for a number of para- and meta-substituted aromatic phosphines were calculated using R(O)MP2/6-311++g(d, 2p)//(U)B3LYP/6-31g(d) method. The results showed the importance of the radical effect as well as the ground effect on the BDEs. For X=H case, because the substituent affected the neutral phosphine to the same extent as it affected the radical, substituent, effects on the P-H BDE were small (rho(+) = 0.28 kJ/mol). In comparison, for X = F or Cl case, because the substituent affected the neutral phosphine much more strongly than it affected the radical, substituent effects on the P-F (rho(+) = -3.25 kJ/mol) or P-Cl (rho(+) 1.31 kJ/mol) BDEs were significant. Therefore, the substituent effects on BDEs of the Z-X, bonds in compounds of the general formula 4-YC(6)H(4)Z-X varied when X changed, which meant that a recent proposal (J. Am. Chem. Soc., 123, 5518 (2001)) was unfortunately not supported.