Abstract
Density functional theory calculations on neutral sheet models for methylaluminoxane (MAO) indicate that these structures, containing 5-coordinate and 4-coordinate Al, are likely precursors to ion-pairs seen during the hydrolysis of trimethylaluminum (Me(3) Al) in the presence of donors such as octamethyltrisiloxane (OMTS). Ionization by both methide ([Me](-) ) and [Me(2) Al](+) abstraction, involving this donor, were studied by polarizable continuum model calculations in fluorobenzene (PhF) and o-difluorobenzene (DFB) media. These studies suggest that low MW, 5-coordinate sheets ionize by [Me(2) Al](+) abstraction, while [Me](-) abstraction from Me(3) Al-OMTS is the likely process for higher MW 4-coordinate sheets. Further, comparison of anion stabilities per mole of aluminoxane repeat unit (MeAlO)(n) , suggest that anions such as [(MeAlO)(7) (Me(3) Al)(4) Me](-) =[7,4](-) are especially stable compared to higher homologues, even though their neutral precursors are unstable.