Reactions of group 3 metal alkyls in the gas phase. Part 9.—Addition of propene to trimethylaluminium

Abstract

The thermal gas phase reaction of propene with monomeric trimethylaluminium has been studied at temperatures from 455 to 549 K using a static reaction system and Teflon coated reaction vessels. Initial propene pressures ranged from 190 to 370 Torr (25.33 to 49.33 kN m^–2) and the ratio of propene to AlMe₃ varied from 4.9 to 24.1. Overall conversions between 0.4 and 12.4 % with respect to alkyl groups were observed. In excess propene the overall reaction involves the rate determining addition of propene to the Al—CH₃ bond (k₁) to give Me₂AlBuⁱ followed by the fast elimination of isobutene and subsequent addition of propene to Me₂AlH, yielding Me₂AlPrⁿ.

The rate constant k₁, corrected for path degeneracy, is given (with standard errors) by the Arrhenius relationship log(k₁/l. mol^–1 s^–1)= 5.60 ± 0.18 –(20.35 ± 0.44)/θ where θ= 2.303 RT/kcal mol^–1.

These results when compared with earlier data for the systems AlEt₃+ ethylene and AlMe₃+ ethylene appear to support a one-step 4-centre concerted process rather than the concept of olefinaluminium alkyl complexes as intermediates formed in these reactions, as proposed earlier.