Development of homogeneous and heterogeneous alkylalumoxane catalysts
Obrey, Stephen J.
Barron, Andrew R.
Doctor of Philosophy
A new type of heterogeneous alkylalumoxane olefin polymerization catalyst, n-MAO, has been synthesized using carboxylate-alumoxane nanoparticles as the support material. This new catalyst has a comparable activity for ethylene polymerization to those of traditional heterogeneous catalysts with similar Al:Zr ratios, but shows a better catalytic activity per unit mass of catalyst. In an effort to develop alternative routes for the formation of methylalumoxane, MAO, the reaction of trimethylaluminum with tertiary group 14 hydroxides (Ph 3EOH) has been investigated. Two distinct mechanisms are observed depending on the relative basicity of the hydroxide. In the case of the basic hydroxides, Ph3SnOH and Ph3PbOH, a hydroxide/alkyl exchange reaction results in the formation of MAO. In contrast, reaction of AlMe3 with acidic hydroxides, Ph3EOH (E = C, Si, Ge), results in alkane elimination and the formation of [Me2Al(mu-OEPh3)] 2. The thermal decomposition of [Me2Al(mu-OCPh3)] 2 to yield MAO is found to be catalyzed by the addition of a Lewis acid, AlClxMe3-x (x = 0--3), however, the MAO product is also an efficient catalyst for the reaction. The overall rate of MAO formation is dependent on the concentration of the Lewis acid and the product (MAO), as well as the nature of the tertiary alcohol. In contrast to the reaction of [Me2Al(mu-OCPh3)]2 with a Lewis acid, the reaction of [Me2Al(mu-OCPh3)]2 with a Lewis base, THF, results in ligand disproportionation to yield MeAl(mu-OCPh 3)2(THF). A new hydrogen bond stabilized gallium alkoxide complex, [Ga2(tBu)4(neol-H)2] (Neol-H2 = 2,2-dimethyl-1,3-propanediol) has been synthesized. This complex has been shown to act as a flexible, strong ligand field, bifunctional (two OH) tetradentate (4O) ligand to first row transition metals in square planar environments.