Interaction of Neutral Donors with Methylaluminoxane

Methylaluminoxane (MAO) is a key activator for olefin polymerization catalysts, making its chemistry of ongoing interest. Neutral donors such as octamethyltrisiloxane (OMTS) are effective abstractors of the dimethylaluminum cation, [Me₂Al]⁺, from methylaluminoxane (MAO), and this process can be readily investigated using electrospray ionization mass spectrometry (ESI-MS) in fluorobenzene (PhF) solution. Complementary studies employing 1D and 2D ¹H NMR spectroscopic studies in bromobenzene-d₅ solution provide details on the extent of ionization vs. donor-acceptor complex formation. DFT studies employing different neutral model precursors and mono- vs. bi-dentate donors shed light on possible mechanisms for ion-pair formation.