Gallium hydride complexes stabilised by multidentate alkoxide ligands: precursors to thin films of Ga2O3 at low temperatures.
The donor-functionalised alkoxides {Me(3-x)N(CH(2)CH(2)O)(x)} (L(x); x = 1, 2) have been used to form gallium hydride complexes [{GaH(2)(L(1))}(2)] and [{GaH(L(2))}(2)] that are stable and isolable at room temperature. Along with a heteroleptic gallium tris(alkoxide) complex [Ga(L(1))(3)] and the dimeric complex [{GaMe(L(2))}(2)], these compounds have been used as single-source precursors for the deposition of Ga(2)O(3) by aerosol-assisted chemical vapour deposition (AACVD) with toluene as solvent. The resulting films were mostly transparent, indicating low levels of carbon contamination, and they were also mainly amorphous. However, [Ga(L(1))(3)] did contain visibly crystalline material deposited at a substrate temperature of 450 °C, by far the lowest ever observed for the CVD of gallium oxide.
Synthesis and structures of gallium alkoxides
Homoleptic gallium tris(alkoxides) [Ga(OR)3]2 were prepared by the reaction of [Ga(NMe2)3]2 (1) and excess ROH (R = CH2CH2NMe2 (2), CH(CH3)CH2NMe2 (3), C(CH3)2CH2OMe (4), CH2CH2OMe (5)) in toluene at room temperature. Compounds 2–5 were isolated as colourless oils. The side-products, [Ga(OCH2CH2NMe2)2Cl] (6), [Ga(OCH(CH3)CH2NMe2)2Cl] (7) and [Ga(OC(CH3)2CH2OMe)Cl2]2 (8) were also isolated in low yield during the synthesis of 2, 3 and 4, respectively. However, compounds 6 and 7 were also prepared directly from the reaction of [Ga(NMe2)2Cl] and 2 equivalents of ROH (6, R = CH2CH2NMe2; 7, R = CH(CH3)CH2NMe2). Similarly, compound 8 was isolated from the reaction of [Ga(NMe2)Cl2] and 1 equivalent of HOC(CH3)2CH2OMe. Single crystal X-ray crystallography showed that the gallium bis(alkoxides) (6 and 7) are monomeric in the solid state with the gallium centre adopting a distorted trigonal bipyramidal geometry. In contrast, the gallium mono(alkoxide) 8 is dimeric.
Sterol metabolism. XLI. Cholesterol A-ring autoxidations
Abstract Chromatographic and spectral evidence is adduced for the presence of cholest-5-en-3-one, cholest-4-en-3-one, and cholest-4-ene-3,6-dione in samples of cholesterol aged naturally in air or subjected to irradiation in air by 60 Co gamma radiation. These findings establish an additional mode of air oxidation of cholesterol to A-ring 3-ketones. Moreover, the oxidation by air of cholest-5-en-3-one induced by 60 Co gamma radiation yielded cholest-4-en-3-one, cholest-4-ene-3,6-dione, and the epimeric 3-oxocholest-4-ene-6-hydroperoxides. Cholest-4-en-3-one was not altered by irradiation in air, nor was cholesterol isomerized to cholest-4-en-3β-ol upon irradiation. From these observations it is deduced that the radiation-induced A-ring dehydrogenation of cholesterol yields initially cholest-5-en-3-one which upon isomerization yields cholest-4-en-3-one not further oxidized and which by a second oxidation yields the epimeric 3-oxocholest-4-ene-6-hydroperoxides which decompose to cholest-4-ene-3,6-dione.