Precursors for pyromellit-bridged silica sol–gel hybrid materials

Abstract

Bridged bis(trialkoxysilylalkyl)pyromellitic diimides 3–6 were prepared as single-source precursors for sol–gel derived organic–inorganic hybrid materials. The synthesis route starts with the formation pyromellit diimide 1 from pyromellitic dianhydride and hexamethyldisilazane (HMDS), followed by metallation of the NH groups to give the dipotassium salt 2. The four molecular hybrid precursors 3–6 were obtained according to the first step of the Gabriel synthesis. The reaction rates were studied as a function of the alkyl chain length and the nature of the halide (Cl vs. I). All products 1–6 were comprehensively analysed using FT-IR, 1H and 13C NMR spectroscopy as well as elemental analysis, and – in the case of 3–6 – also with 29Si NMR spectroscopy. For compounds 3 (with propylene groups and methoxy substituents) and 6 (with methylene groups and ethoxy substituents) single crystal X-ray structures were determined and discussed. Hydrolysis and condensation of the alkoxides 3–6 were carefully monitored with solution 29Si and 1H NMR spectroscopy providing a basis for further studies on the formation of silica-pyromellit organic–inorganic hybrids from precursors 3–6. Finally the formation of flexible and transparent hydride films using precursors 4 and 6 was proved.