Effects of aging of rutheniumporphyrins on their catalytic activity

In this work we studied the effect of the storage conditions of the (carbonyl)[tetrakis(5,10,15,20-2-bromophenyl)porphyrinate]ruthenium(II) (RuBr4TPP)-Br-II and (carbonyl)[tetrakis(5,10,15,20-2-nitrophenyl)porphyrinate]ruthenium(II) Ru-II(NO2)(4)TPP complexes on their catalytic activity. The catalytic activity was monitored by the oxidation of cyclohexane with iodosylbenzene. The syntheses of porphyrin ligands were carried out by reaction of pyrrole with 2-bromobenzaldehyde or 2-nitrobenzaldehyde. Ruthenium(II)porphyrins were obtained by the addition of a ruthenium trichloride hydrate solution to the ligand solution, under reflux and constant flow of carbon monoxide. The porphyrin ligands and metalloporphyrins were characterized by UV-Vis and infrared spectra spectroscopy. The complexes were stored in four basic conditions: under argon atmosphere and in open flasks, at room temperature and low temperature (refrigerator). This article presents the results using catalysts stored in two conditions, argon atmosphere and in open flasks, at room temperature. For the catalysts stored in low temperature, the results were the same for the complexes stored at room temperature. At determined intervals, the complexes were used as catalysts under the same reaction conditions. The products were analyzed by gas chromatography. The study of the complexes aging was monitored by diffuse reflectance infrared spectroscopy, DRIFT, and UV-Vis spectroscopy. The present work showed that in all the cases studied there was a decrease in the total percentage of products for a long time of catalysts storage. This was very pronounced for the complexes stored in open flasks indicating that oxygen atmospheres favor the formation of not catalytically active species. (C) 2003 Elsevier B.V. All rights reserved.