Little MAO: Isolation of an {Al₄} Methylalumoxane Species from the Reaction of Trimethylaluminum with Water

Low-temperature hydrolysis of AlMe3 using THF as a solvent affords the isolable alumoxane “MAO” species [(Me2Al)2O(thf)]2. Solution NMR studies revealed the dissociation of [(Me2Al)2O(thf)]2 into two (Me2Al)2O(thf)2 molecules, in the presence of THF. The reaction of dimeric [(Me2Al)2O(thf)]2 with 2,6-diisopropylphenol leads to [Me2AlOAlMe(OC6H3iPr2-2,6)] and [Me2Al(μ-OC6H3iPr2-2,6)]2 as a side product. Both the [(Me2Al)2O(thf)]2 dissociation and the oxy/aryloxy exchange document highly fluxional alumoxane behavior involving Al–O bond breaking and bond formation. When combined with 10 equiv of AlMe3, MAO species [(Me2Al)2O(thf)]2 activates Cp2ZrMe2 to promote propylene polymerization.