Reactions of Group 3 Metal Alkyls in the Gas Phase*: Part 8.—Homogeneous Thermal Unimolecular Elimination of Ethylene from Triethylaluminium

Abstract

The kinetics of the homogeneous gas-phase elimination of ethylene from triethylaluminium have been studied in the presence of excess propene in the temperature range 426-488 K. The observed first-order rate constants based on the loss of ethyl groups fit the Arrhenius relationship, log k'o/s"1 10.93 ±0.13-(30.05 ±0.27)/0, where 0 = 4.58 x 10-3 Tin units of kcal mol"1t [= 10.93 ± 0.13 —(125.7 ±1.1)/19.15 x 10-3 T in units of kJ mol-1]- These activation parameters arc compatible with the 4-centrc polar transition state proposed for olefin eliminations from other Group 3 metal alkyls, and the ctTect of ^-substitution on the rate of elimination is additive. The activation energy for the back-addition of ethylene to dialkylaluminium hydride is estimated to be 4.9 kcal mol-1.