Encapsulation of tetraazaannulenato compounds in matrix by sol-gel process

The hybrid organic-inorganic catalyst constituted by {5,7,12,14-tetramethyldibenzo[b,i]-1,4,8,11-tetraaza[14] annulenato} nickel (II), NiTMTAA, encapsulated in an alumina matrix has been prepared. NiTMTAA was synthesized by the reaction of nickel acetate with o-phenylenediamine in the presence of 2,4-pentanedione under argon atmosphere. The alumina hybrid material was obtained by a non hydrolytic sol-gel route, through the condensation of aluminum chloride with diisopropylether in the presence of NiTMTAA. The material has been prepared through precipitation from a gel. Characterization of the alumina hybrid material has been performed by ultra violet-visible spectroscopy, electron spectroscopic imaging, surface area, atomic absorption, infrared spectroscopy, and thermogravimetric analysis. The ultra violet-visible absorption spectrum of the hybrid material has bands characteristic of the NiTMTAA compound showing that the structure of NiTMTAA has been preserved in the hybrid material. The new material has a surface area of 300 m(2)/g. The electron image was that of a non-crystalline microstructure. Comparison between the leaching of NiTMTAA from NiTMTAA adsorbed on commercial neutral alumina confirm that in the non-hydrolytic materials the NiTMTAA is entrapped and not only adsorbed on the alumina surface. The use of conventional hydrolytic sol-gel process leads to the complete leaching of NiTMTAA from matrix, underlining the importance of the non-hydrolytic alumina gel process in the matrix preparation. The new catalysts prepared were tested for their ability to catalyze the epoxidation of (Z)-cyclooctene using iodosylbenzene as oxygen donor, giving moderate yields in the epoxidation (40%), while the homogeneous NiTMTAA is inactive due to NiTMTAA bleaching. These results emphasize the effect of the non-hydrolytic alumina matrix to prevent chemical degradation of NiTMTAA.