Cuprous Tris(<i>tert</i>-butoxy)siloxy Complexes and Their Thermolytic Conversion to Copper−Silica and Copper Oxide−Silica Nanocomposites

The (tert-butoxy)siloxy complex [CuOSi(OtBu)3]4 (1) was prepared by silanolysis of [CuOtBu]4 with (tBuO)3SiOH and examined as a single-source precursor to Cu/SiO2 and CunO/SiO2 (n = 1, 2) materials. The related complex {Cu[μ-OSiPh(OtBu)2]}4 (4), obtained similarly, was characterized by X-ray crystallography as having a planar Cu4O4 core with oxygen-bridged Cu atoms. The highly associated, sublimable {NaCu[OSi(OtBu)3]2}6 (3) was obtained by the addition of NaOSi(OtBu)3 to 1 or by reaction of 2 equiv of NaOSi(OtBu)3 with CuCl. Thermogravimetric analysis (TGA) of 1 under both oxygen and argon reveals rather sharp, low-temperature conversions to the final ceramic compositions (onset temperatures: ca. 100 °C under oxygen; ca. 150 °C under argon). Under argon, the resulting material consists of Cu0 and Cu2O nanoparticles dispersed in silica, whereas an oxygen atmosphere leads to CuO nanoparticles in silica. These materials are carbon- and hydrogen-free and are produced by elimination of isobutene, tert-butyl alcohol, water, and silanol. The pyrolytic conversion of compound 4 occurs at higher temperature and more gradually but gives relatively clean conversion to a CuO/SiO2 composite under an oxygen atmosphere. The volatility of 1 allows its use in CVD preparations of thin films. Amorphous thin films with a Cu/Si ratio of 1:0.85 (microprobe analysis) and thicknesses ranging from 200 nm to 6 μm have been obtained.