A new precursor, [RA1(μ-NHEt)(μ-NEt)₂Si(NHEt)]₂ (R = Et, Me), is proposed for the preparation of high-surface-area silicon aluminum nitride based xerogels. The conversion is carried out using ammonia gas and pentane/ammonia mixtures at low (1 bar) and high (200 bar) pressure. Materials with specific surface areas up to 800 m² g^-1 are obtained under high-pressure conditions. The enrichment of aluminum in the materials obtained at low pressure indicates the formation of Si(NHEt) ₄ as a side product that is also detected in NMR spectra. In scanning and transmission electron micrographs the materials appear with a flakelike morphology. The presence of NH groups is detected in IR spectra, and the ²⁹Si MAS NMR signal is detected at -40.5 ppm. The materials are X-ray amorphous. The composition varies with the reaction conditions. After a high-pressure transformation, the Al/Si ratio is close to 1.0 (Al2-Si _1.8N_8.7C_1.3H_11.6) but transformation at low NH₃ pressure only produces Al-enriched materials. The solid imides are efficient catalysts for the Michael addition of malononitrile to acrylonitrile with a high yield of 96% after 5 h.