The reaction of mesoporous silica (SBA15) dehydroxylated at 700 °C, with di-isobutyl aluminum hydride, i- Bu2AlH, gives after thermal treatment single site tetrahedral aluminum hydride with high selectivity. The starting aluminum isobutyl and the final aluminum hydride are fully characterized by FT-IR, advance SS-NMR spectroscopy [1H, 13C, multiple quanta (MQ) 2D 1H-1H and 27Al] and elemental analysis, while DFT calculations provide a rationalization of the occurring reactivity. Trimeric i-Bu2AlH reacts selectively with surface silanols without affecting the siloxane bridges. Its hydride analogous catalyzes ethylene polymerization. Interestingly, the weakly coordinated siloxane bridge of the surface plays the role of a precise ligand, which most likely exchanges with the C=C bond during the catalysis. Indeed, catalytic tests show that this single aluminum hydride site is active in the production of low-density polyethylene. By comparison, monomeric triisobutylaluminum (i-Bu3Al) leads to a very complex surface coordination of aluminum on the surface and the production of linear high-density polyethylene.

Single site tetra-coordinated aluminium hydride supported on mesoporous silica. From dream to reality!

253rd National Meeting (2017)

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