RHODIUM COMPLEXES WITH NITROGEN-DONOR LIGANDS ANCHORED ON SILICIC SUPPORTS .1. SYNTHESIS AND CHARACTERIZATION

An amino-functionalized silica, (SiO2)O3/2Si(CH2)3NH2 (I) has been synthesized by cohydrolysis of tetraethylorthosilicate (TEOS) and (3-aminopropyl)triethoxysilane (APS), following an acid-catalyzed sol-gel process. The primary amine functions of I, by reaction with diketones or pyridine-2-carboxaldehyde, create "in situ" diazabutadiene (R-DAB) or pyridinecarbiimine (R-PyCa) ligands grafted to the silicic support. By subsequent reaction of these N-donor groups with RhCl3.3H2O or various organometallic complexes of rhodium, we have obtained anchored rhodium complexes homogeneously dispersed on the silicic support. The results obtained by this route have been compared with those obtained by forming first the rhodium complex with a ligand derivative from R-propyltriethoxysilane (R = amine, DAB, PyCa) and its subsequent copolymerization with TEOS. Some experiments with silica gel (Kieselgel-60) carried out in parallel have enabled us to study the differences between this silica matrix and that generated from TEOS. These organo-inorganic materials were characterized by elemental analysis, TEM-EDX techniques and IR, CP-MAS C-13 NMR, and XPS spectroscopy.