Structure and Reactivity of Al-O(H)-Al Moieties in Siloxide Frameworks: Solution and Gas-Phase Model Studies.

Even though aluminas and aluminosilicates have found widespread application, a consistent molecular understanding of their surface heterogeneity and the behavior of defects resulting from hydroxylation/dehydroxylation remains unclear. Here, we study the well-defined molecular model compound, [Al (μ -OH) (THF) (PhSi(OSiPh O) ) ], 1, to gain insight into the acid-base reactivity of cyclic trinuclear Al (μ -OH) moieties at the atomic level. We find that, like zeolites, they are sufficiently acidic to catalyze the isomerization of olefins.

Trapping Aluminum Hydroxide Clusters with Trisilanols during Speciation in Aluminum(III)-Water Systems: Reproducible, Large Scale Access to Molecular Aluminate Models.

To gain molecular level insights into the properties of certain functions and units of extended oxides/hydroxides, suitable molecular model compounds are needed. As an attractive route to access such compounds the trapping of early intermediates during the hydrolysis of suitable precursor compounds with the aid of stabilizing ligands is conceivable, which was tested for the aluminum(III)/water system. Indeed, trisilanols proved suitable trapping reagents: their presence during the hydrolysis of Al(i) Bu2 H in dependence on the amount of water used allowed for the isolation of tri- and octanuclear aluminum hydroxide cluster complexes [Al3 (μ2 -OH)3 (THF)3 (PhSi(OSiPh2 O)3 )2 ] (1) and [Al8 (μ3 -OH)2 (μ2 -OH)10 (THF)3 (p-anisylSi(OSiPh2 O)3 )4 ] (2).