Chlorination of p-substituted triarylpnictogens by sulfuryl chloride: Difference in the reactivity and spectroscopic characteristics between bismuth and antimony

Competitive oxidative chlorination of p-substituted triarylstibines 3 [(p-XC6H4)3Sb; a: X = OMe, c: Cl, d: CO2Et, e: CF3, f: CN, g: NO2] by sulfuryl chloride was carried out against 3b (X = H) and the electronic effect of these substituents on the chlorination of 3 was compared with that of homologous triarylbismuthanes 1. The relative ratios 4/4b (Ar3SbCl2/Ph3SbCl2) decreased with increasing electron-withdrawing ability of the substituents (a: 53/47, c: 49/51, d: 46/54, e: 44/56, f: 40/60, g: 37/63), but the tendency was not so pronounced as observed in the chlorination of 1. A Hammett plot of the 4/4b ratios against the σp constants exhibited a good linear relationship with a negative slope, the value of which was almost half of that deduced from the 2/2b (Ar3BiCl2/Ph3BiCl2) ratios. The difference in the reactivity between 1 and 3 may be explained by the effect of the electron-withdrawing substituents in the aromatic rings, which affects the p-character of the lone pair on the pnictogen atoms by increasing the positive metal charge and appears more remarkably in 1 than in 3. The 13C NMR study of 3 revealed that the chemical shifts of the ipso carbons (C1) attached to the antimony show a linear relationship against the σp constants with a positive slope (14.5). The value was smaller than that deduced from 1 (17.0), suggesting that the antimony center of 3 is less sensitive to the substituent effect. This is in accord with the tendency of the chlorination.

Oxidative chlorination of p-substituted triarylstibines was carried out and the effect of the p-substituents on the chlorination was compared with that of the bismuth congeners. The spectroscopic characteristics of the stibines and their dichlorides were studied by 13C NMR spectrum.Figure optionsDownload as PowerPoint slide