124088-77-3Relevant academic research and scientific papers
Aluminum alkoxides as synthons for methylalumoxane (MAO): Product-catalyzed thermal decomposition of [Me2Al(μ-OCPh3)]2
Obrey, Stephen J.,Bott, Simon G.,Barron, Andrew R.
, p. 5162 - 5170 (2008/10/08)
The thermal decomposition of [Me2Al(μ-OCPh3)]2, to yield Ph3CMe and methylalumoxane ([MeAlO]n, MAO), is initially catalyzed by the addition of AlMe3; however, the reaction is also catalyzed by the MAO product. The overall reaction rate takes the form: rate = kTMA[{Me2Al(μ-OCPh3)}2][AlMe 3] + kMAO[{Me2Al(μ-OCPh3)}2][MAO], where kMAO ? kTMA. The ΔH? for the AlMe3- and MAO-catalyzed reactions have been determined as 175 ± 8 and 190 ± 15 kJ·mol-1, respectively. Both reactions show a large positive value of ΔS? (41 ± 8 eu and a dissociative reaction. The thermal decomposition of [Me2Al(μ-OCPh3)]2 is also catalyzed by Lewis acids, including AlCl3, AlCl2Me, and AlClMe2. On the basis of the relative rates of the AlMe3-catalyzed thermal decomposition of [Me2Al-(μ-OCPh3)]2, [Me2Al(9-Ph-fluoroxy)]2 (1), and [Me2Al(9-Me-fluoroxy)]2 (2) and the MAO-catalyzed C-methylation of [Me2Al(μ-OR)]2 [R = CMePh2 (3), CMe2Ph (4), CH2Ph, C6H11, C6H4-4-tBu (5)], it is proposed that the rate-determining step for C-methylation involves heterolytic cleavage of the O-C bond and the formation of a carbonium ion. The more stable the carbonium ion, the faster the reaction. Additionally, it is proposed that Lewis acid catalysis is due to the formation of an asymmetrically bridged hemi-alkoxide, whose formation is an equilibrium process such that the observed rate of the reaction will be dependent on the equilibrium for the reaction of [Me2Al(μ-OCPh3)]2 with the Lewis acid.
