Allen W. Apblett

From minerals to materials: synthesis of alumoxanes from the reaction of boehmite with carboxylic acids

Reaction of pseudo-boehmite, [Al(O)(OH)]n, with carboxylic acids (RCO2H) results in the formation of the carboxylatoalumoxanes, [Al(O)x(OH)y(O2CR)z]n where 2x + y + z = 3 and R = C1–C13. The physical properties of the alumoxanes are highly dependent on the identity of the alkyl substituents, R, and range from insoluble crystalline powders to powders which readily form solutions or gels in hydrocarbon solvents, from which films may be readily spin-coated. The physical and chemical changes that occur during the reaction of boehmite with carboxylic acids, and the resulting alumoxanes, have been characterized by scanning electron and transmission electron microscopy (SEM and TEM), IR and multinuclear NMR spectroscopy, and thermogravimetric/differential thermal analysis (TG/DTA). The carboxylatoalumoxanes reported herein are spectroscopically similar to analogues prepared from small molecule precursors. Based on the IR and NMR spectra of the alumoxanes as well as comparison with the aluminium carboxylate compounds [Me2Al(µ-O2CR)]2 and Al(O2CR)(salen)(R = CH3, n-C5H11), a model structure of the alumoxanes is proposed, consisting of a boehmite-like core with the carboxylate substituents bound in a bridging mode. Furthermore, the alumoxane particles appear as rod or sheet-like particles, not linear polymers. This is proposed to be due to the destruction of hydrogen bonding within the mineral as hydroxide groups are removed and replaced with acid functionalities. All of the alumoxanes decompose under mild thermolysis to yield alumina. Mass spectral studies indicate that upon thermolysis the volatile decomposition products are water and the carboxylic acid.

Oxidation and hydrolysis of tris-tert-butylgallium

Abstract The oxidation of GaBu3t with oxygen leads to the formation of [Bu3tGa(μ-OOBut)]2 (1). The thermolysis of 1 yields the alkoxide complex [Bu2tGa(μ-OBut)]2 (2), which may also be prepared directly from GaBu3t and ButOH. The reaction of [ButGaCl(μ-Cl)]2 (3) with oxygen does not result in its oxidation, but may be used in its purification due to the oxidation of the GaBu3t impurities. The hydrolysis of GaBu3t in thf solution, in which it exists as the solvated complex 4, results in the formation of the monomeric hydroxide complex Bu2tGa(OH)(thf) (5). In contrast, the use of non-coordinating solvents results in the trimeric hydroxide [Bu2tGa(μ-OH)]3 (6). Compound 6 is also isolated from the reaction of Bu2tGaCl(thf) (7) with KOH in refluxing thf. The solid state pyrolysis of 6 gives the polymeric oxide [ButGa(O)]x (8). All the compounds have been characterized by NMR, IR and mass spectroscopy, while the structures of 1, 2 and 3 have been confirmed by X-ray crystallography. Compound 1 crystallizes in the monoclinic space group C2/m with a = 16.375(2), b = 11.323(2), c = 8.895(2) A and β = 116.710(12)°, Z = 2, R = 0.042 and Rw, = 0.038. Compound 2 crystallizes in the orthorhombic space group Pbca with a = 15.0072(17), b = 9.8399(8), c = 18.3840(15) A, Z = 4, R = 0.037 and Rw = 0.041. Compound 3 crystallizes in the monoclinic space group P21/c with a = 6.816(4), b = 6.743(5), c = 17.062(10)A and β = 95.87(4)°, Z = 2, R = 0.042, Rw = 0.049.

Siloxy-substituted alumoxanes: synthesis from polydialkylsiloxanes and trimethylaluminium, and application as aluminosilicate precursors

The interaction of AlMe3 with the polydialkylsiloxanes (OSiRMe)x and (OSiPh2)3 for long periods at elevated temperatures leads to the rupture of the silicon–oxygen framework and yields dimeric dimethylaluminium siloxides [Me2Al(OSiMe2R)]2, R = Me (1), n-C6H13(2), n-C8H17(3), n-C14H29(4), n-C18H37(5), -CH2CH2CF3(6), Ph (7), and [Me2Al(OSiMePh2)]2(8), respectively. Hydrolysis of the dimethylaluminium siloxides results in the formation of oligomeric siloxy-substituted alumoxanes having the composition [Al(O)(OH)x(OSiMe2R)1–x]n, R = Me (9), n-C6H13(10), n-C8H17(11), n-C14H29(12), n-C18H37(13), –CH2CH2CF3(14), Ph (15), and [Al(O)(OH)x(OSiMePh2)1–x]n(16). The extent of hydrolysis, physical properties, and the ceramic yield of aluminosilicate upon their pyrolysis are highly dependent on the nature of the alkyl substituent, R, on silicon. The aluminium siloxides and siloxy-alumoxanes have been characterised by IR, 1H, 13C, 17O, 27Al and 29Si NMR spectroscopy, mass spectrometry, thermogravimetric analysis, X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray (EDX) analysis. The aluminosilicate has been characterised by scanning electron microscopy (SEM), EDX, XPS and X-ray diffraction (XRD).

Chemical vapour deposition of aluminium silicate thin films

Aluminium silicate, (Al2O3)x(SiO2)y, thin films have been grown by atmospheric pressure metal-organic vapour deposition using the volatile metal organic precusor [Al(OSiEt3)3]2. As determined by X-ray photoelectron spectroscopy, the deposited films consisted of a mixture of Al2O3, SiO2, and an aluminosilicate.

From Minierals to Materlals: A Facile Synthetic Route to Preceraic Polymers for Aluminum Oxide

Abstract : Reaction of boehmite, (Al(O)(OH)n, with an excess of carboxylic acid (HO2CR) results in the formation of the carboxy substituted alumoxanes, (Al(O) x(OH)y(O2CR)z)n where 2x + y + z = 3 and R = alkyl substituents. The alumoxanes have been fully characterized by SEM, elemental analysis, IR and multinuclear NMR spectroscopy. The physical properties of the alumoxanes are highly dependent on the identity of R, and range from insoluble crystalline powders, e.g. R = CH3, to powders which readily form solutions or gels in hydrocarbon solvents, e. g. R = C5H11. All of the alumoxanes decompose under mild thermolysis to yield gamma-alumina.

The molecular structure of (allyl)bis(methylcyclopentadienyl)niobium(III)

Abstract The compound (η 5 -C 5 H 4 Me) 2 Nb(η 3 -C 3 H 5 ) ( 1 ) has been prepared and characterized by 1 H, 13 C and 93 Nb NMR spectroscopy. The molecular structure of 1 has been confirmed by X-ray crystallography and the nature of the bonding between the allyl ligand and the niobium is discussed. Compound 1 crystallizes in the monoclinic space group P 2 1 / c , a = 6.029(2), b = 7.752(2), c = 26.115(6) A, β = 92.33(2)°, V = 1219.5(5) A 3 , Z = 4, R = 0.031, R w = 0.050.