Y. Kawasaki, Tsunenori Takahashi, Atsushi Fujioka
May 10, 1977
Journal of Organometallic Chemistry
Abstract The rate constants, k, and activation parameters, Ea, △H≠, △S≠ and △G≠, were determined by the 1H NMR line broadening technique for the following halogen exchange reactions: (CH3)n(C6H5)3−nSb(L) [Cl↔Br] (L = 8-quinolinolato ligand and its 2−, 4−, 5−, 7-methyl, 5-chloro, 5-acetyl, 5-nitro and 5,7-di- chloro derivative; n = 1−3). The rate constant and activation energy for these halogen exchange reactions were found to decrease as the number of the phenyl groups increased. The value of the activation entropy became increasingly negative in the above order. The halogen exchange reactions of the above system were found to proceed through a bridging intermediate. In the (CH3)2C6H5Sb(L) [Cl↔Br] system, the rate constant decreased and the activation energy became large when an electron-withdrawing group was introduced into the 5-position of the 8-quinolinolato ligand. Linear relations were obtained between Taft's σ° value and log(k/k0 ), and the activation entropy and activation enthalpy. In CH3(C6H5CH2)C6H5Sb(2-MeOx)O2CCH3, a pentacoordinate antimony atom was found to be a chiral center (Ox = oxinato ligand).