Methylaluminoxane (MAO) is a key activator for olefin polymerization catalysts, making its chemistry of ongoing interest. Strong and bidentate neutral donors such as 2,2′-bipyridine are effective abstractors of the dimethylaluminum cation, [Me 2 Al] + , from methylaluminoxane (MAO), while monodentate, weaker donors such as THF appear most prone to adduct formation with both free and bound trimethylaluminum. The ionization process can be readily investigated using electrospray [a]

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 (Me3Al) in the presence of donors such as octamethyltrisiloxane (OMTS). Ionization by both methide ([Me]−) and [Me2Al]+ 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 [Me2Al]+ abstraction, while [Me]− abstraction from Me3Al‐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(Me3Al)4Me]−=[7,4]− are especially stable compared to higher homologues, even though their neutral precursors are unstable.

Ionized methylalumoxane exchanges alkyl groups rapidly with trialkylaluminums in solution, generating statistical mixtures of modified methylalumoxane anions.

Methylalumoxane (MAO), a perennially useful activator for olefin polymerization precatalysts, is famously intractable to structural elucidation, consisting as it does of a complex mixture of oligomers generated from hydrolysis of...

Kinetic profiles obtained from monitoring the solution phase substitution chemistry of [Ru(η 5 -indenyl)(NCPh)(PPh 3 ) 2 ] + (1) by both ESI-MS and 31 P{ 1 H} NMR are essentially identical, despite an