Spectroscopic Studies of Synthetic Methylaluminoxane: Structure of Methylaluminoxane Activators |
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| Authors: | Dr Anuj Joshi Dr Scott Collins Prof Mikko Linnolahti Dr Harmen S Zijlstra Elena Liles Prof J Scott McIndoe |
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| Institution: | 1. Department of Chemistry, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 5C2 Canada;2. C/o Department of Chemistry, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 5C2 Canada;3. Department of Chemistry, University of Eastern Finland, Joensuu Campus, Yliopistokatu 7, 80100 Joensuu, Finland |
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| Abstract: | Hydrolysis of trimethylaluminum (Me3Al) in polar solvents can be monitored by electrospray ionization mass spectrometry (ESI-MS) using the donor additive octamethyltrisiloxane (Me3SiO)2SiMe2, OMTS]. Using hydrated salts, hydrolytic methylaluminoxane (h-MAO) features different anion distributions, depending on the conditions of synthesis, and different activator contents as measured by NMR spectroscopy. Non-hydrolytic MAO was prepared using trimethylboroxine. The properties of this material, which contains incorporated boron, differ significantly from h-MAO. In the case of MAO prepared by direct hydrolysis, oligomeric anions are observed to rapidly form, and then more slowly evolve into a mixture dominated by an anion with m/z 1375 with formula (MeAlO)16(Me3Al)6Me]?. Theoretical calculations predict that sheet structures with composition (MeAlO)n(Me3Al)m are favoured over other motifs for MAO in the size range suggested by the ESI-MS experiments. A possible precursor to the m/z 1375 anion is a local minimum based on the free energy released upon hydrolysis of Me3Al. |
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| Keywords: | ESI-MS methylaluminoxane NMR sheet structures synthesis |
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