Formation of Lewis Acidic Support Materials via Chemisorption of Trimethylaluminum on Mesoporous Silicate MCM-41

The chemisorption of trimethylaluminum on dehydrated mesoporous MCM-41 is described. The sorption capacity of the silicate material was examined by addition of various amounts of the organoaluminum reagent and monitored by elemental analysis, FTIR spectroscopy, and nitrogen physisorption measurements. Multinuclear ( 1 H, 13 C, 27 Al) solid-state NMR studies reveal a methyl surface population with a SiCH 3 /AlCH 3 ratio of approximately 0.45 and suggest a highly distorted geometry and polarized charge density, respectively, at the aluminum centers. Air-exposed samples indicate the formation of four- and six-coordinate aluminum. The AlMe 3 -modified MCM-41 materials exhibit a strong Lewis acidic behavior, as derived from a novel “test reaction”, involving an intermetallic Lewis acid-base competition reaction between the support system and the spectroscopically versatile, n -hexane-soluble complex Y[N(SiHMe 2 ) 2 ] 3 (THF) 2 . Additionally, the rare earth dimethylsilylamide reagent seems to be a promising probe molecule for examining the alkylation capability of such organoaluminum-modified support materials.