Ga[OSi(O^tBu)₃]₃·THF, a thermolytic molecular precursor for high surface area gallium-containing silica materials of controlled dispersion and stoichiometry

Abstract

The molecular precursor tris[(tri-tert-butoxy)siloxy]gallium, as the tetrahydrofuran adduct Ga[OSi(O(t)Bu)3]3·THF (), was synthesized via the salt metathesis reaction of gallium trichloride with NaOSi(O(t)Bu)3. This complex serves as a model for isolated gallium in a silica framework. Complex decomposes thermally in hydrocarbon solvent, eliminating isobutylene, water, and tert-butanol to generate high surface area gallium-containing silica at low temperatures. When thermal decomposition was performed in the presence of P-123 Pluronic as a templating agent the generated material displayed uniform vermicular pores. Textural mesoporosity was evident in untemplated material. Co-thermolysis of with HOSi(O(t)Bu)3 in the presence of P-123 Pluronic led to materials with Ga : Si ratios ranging from 1 : 3 to 1 : 50, denoted UCB1-GaSi3, UCB1-GaSi10, UCB1-GaSi20 and UCB1-GaSi50. After calcination at 500 °C these materials exhibited decreasing surface areas and broadening pore distributions with increasing silicon content, indicating a loss of template effects. The position and dispersion of the gallium in UCB1-GaSi materials was investigated using (71)Ga MAS-NMR, powder XRD, and STEM/EDS elemental mapping. The results indicate a high degree of gallium dispersion in all samples, with gallium oxide clusters or oligomers present at higher gallium content.

Silica-supported isolated gallium sites as highly active, selective and stable propane dehydrogenation catalysts

“…10 A high-quality X-ray diffraction experiment provides reliable bond distances and angles for this precursor (Fig. 1).…”

“…A two-step approach, involving both SOMC and the thermolytic molecular precursor approach has previously been implemented to generate isolated surface sites with controlled oxidation state and nuclearity. 9 Herein we describe the synthesis, structural characterization of the molecular complex [Ga(OSi(O t Bu) 3 ) 3 (THF)] ( 1 ) 10 and its utilization as a precursor for generating gallium single-sites on silica. These isolated gallium sites were achieved through grafting of 1 on silica followed by a thermolysis step at 500 °C under high vacuum.…”

Enhanced CH3OH selectivity in CO2 hydrogenation using Cu-based catalysts generated via SOMC from GaIII single-sites

“…We rst prepared well-dened Ga III sites on SiO 2 with ca. 1.0 Ga III nm À2 by graing and thermolysis of [Ga(OSi(O t Bu) 3 ) 3 (-THF)]: 41,42 Ga III @SiO 2 (ref. 42) (M x @SiO 2 denoted as isolated M surface sites in its x oxidation state) via an SOMC/TMP approach and then graed [Cu(O t Bu)] 4 on residual surface silanols present in Ga III @SiO 2 .…”

The Power of Non-Hydrolytic Sol-Gel Chemistry: A Review

“…Recently, the Tilley group reported a non-hydrolytic synthesis of high surface area gallium-containing silica materials via the thermal decomposition of a Ga[OSi(O t Bu) 3 ] 3 ·THF molecular precursor [174]. Thermal decomposition in the presence of Pluronic P123 as a templating agent led to a material containing uniform vermicular pores while non-templated samples gave broad pore size distributions.…”

“…The next type of synthetic method employing block copolymer templates was developed by the Tilley group [41,174]. In this case, the multicomponent metal oxides were prepared via the Reproduced with permission from [47].…”