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Pd-complexes of silica-anchored nitrogen containing chelating compounds were prepared by the following reactions: (a) synthesis of the Schiff-bases from 3-aminopropyltriethoxysilane and 2-acetylpyridine, 2-acetylpyrazine or 2,6-diacetylpyridine; (b) reduction of the Schiff-bases with NaBH4 in methanol; (c) cogelification with tetraethyl orthosilicate (TEOS); (d) reaction of the obtained functionalized silica with [PdCl2(PhCN)2] in CH2Cl2. The corresponding model ligands and palladium complexes were also prepared from the reaction of n-propylamine with the pyridine or pyrazine compound, followed by the reduction with NaBH4 and the reaction with [PdCl2(PhCN)2]. The products were characterized by BET, FTIR, GC–MS, 1 H - NMR and elemental C–H–N analysis. The anchored Pd-complexes were tested as catalysts in: (a) the Heck reaction of iodobenzene with ethyl acrylate or styrene in the presence of tributylamine, as base, and toluene or p-xylene, as solvent; (b) the carbonylation reaction of iodobenzene with CO, at atmospheric pressure, in methanol in the presence of triethylamine or potassium acetate, as base. The catalysts were separated from the reaction mixtures and re-used many times. The best results were obtained in both reactions with the anchored Pd-complexes prepared from 2-acetylpyridine: 14 cycles in the Heck reaction ( TON ≃4100 mmol product/mmol Pd) and 20 cycles in the carbonylation of iodobenzene ( TON ≃2300 mmol product/mmol Pd). |
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