Kinetics and mechanism of the reactions of triethylaluminium with phenylacetylene

Abstract

The kinetics of the reactions between triethylaluminium and phenylacetylene have been studied in cyclohexane between 313 and 333 K. Two reactions are observed; metallation, which proceeds by the bimolecular reaction of dimeric triethylaluminium and phenylacetylene with a rate coefficient k₂= 10^{6.8 ± 1.5} e^{–(64000 ± 2900K/8.314T}) dm³ mol^–1 s^–1, and addition which proceeds by way of an alkyne π-complex (I). The equilibrium constant for the formation of (I) has been estimated. The rate controlling step of the addition reaction is a rearrangement of (I), through a four-centre transition state, with a rate coefficient k₁= 10^{11.6 ± 0.9} e^{–(94000 ± 2500K)/8.314T)} s^–1.