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 exam ined by addition of various amounts of the organoaluminum reagent and monitored by elemental analysis, FTIR spectroscopy, and nitrogen physi sorption measurements. Multinuclear (H-1, C-13, Al-27) solid-state NMR studies reveal a methyl surface population with a SiCH3/AlCH3 ratio o f approximately 0.45 and suggest a highly distorted geometry and polar ized charge density, respectively, at the aluminum centers. Air-expose d samples indicate the formation of four-and six-coordinate aluminum. The AlMe3-modified MCM-41 materials exhibit a strong Lewis acidic beha vior, as derived from a novel ''test reaction'', involving an intermet allic Lewis acid-base competition reaction between the support system and the spectroscopically versatile, n-hexane-soluble complex Y[N(SiHM e2)(2)](3)(THF)(2). Additionally, the rare earth dimethylsilylamide re agent seems to be a promising probe molecule for examining the alkylat ion capability of such organoaluminum-modified support materials.