SYNTHESIS OF RUTHENIUM CLUSTERS ON THE SURFACE OF MCM-41 AND SILICA

Abstract

This thesis embodies the results of our studies on the synthesis, characterisation of Si-MCM-41 and surface-mediated carbonylation reactions of ruthenium compounds, RuX3·nH2O (x = Cl, I, OH), with carbon monoxide. In the present study, synthesis of MCM materials was investigated using pure cetyltrimethylammonium hydroxide (CTMAOH), Ludox silica and water. A systematic study was undertaken involving the following parameter: amount of reactants, mixing order, reaction time, ratio of SiO2/CTMAOH and stirring. The materials were characterised by thermogravimetric analysis, low angle X-ray diffraction (XRD), surface area and pore size distribution. The calcined sample had a surface area of about 800 m2 /g, pore size around 30 Å. Pore structure was typical hexagonal channel. Thermal stability of the MCM material was also studied. This MCM material was stable enough for high temperature treatment. In our study, carbonylation of silica-supported RuCl3 was found to be similar to that reported, only Ru(II) chloride carbonyls can be formed, attempts to reduce further were unsuccessful. Using MCM and Merck silica as the support, carbonylation of RuCl3 gave two species Ru(CO)2Cl2(HO-Si ?)2 and Ru(CO)3Cl2(HO-Si ?) selectively, depending on the conditions used. Compounds Ru(CO)2Cl2(L)2 (L = PPhi, AsPhi, Py) and Ru(CO)3Cl2(L) (L = Py, CH3CN, PhCN) were obtained by the reactions of the surface species and the coordinating ligands. The reactivity of the surface species Ru(CO)3Cl2(HO-Si ?), towards the ligands is found to be similar as that of the dimeric compound [Ru(CO)3Cl2]2. The later can be obtained either by subliming or by extracting surface-bound species with weak coordinating solvents. We further found that carbonylation of supported RuI3 gave Ru3(CO)12 and [Ru(CO)3I2]2. The formation of Ru3(CO)12 gave the first example of surface-mediated synthesis of the cluster. This method provided a simple way to Ru3(CO)12 starting from RuI3. Carbonylation of Ru(OH)3 has not been reported by both surface-mediated method and conventional method due to the insolubility of Ru(OH)3, Carbonylation of supported Ru(OH)3 gave Ru3(CO)12 and a new surface species, probably [Ru3(CO)9(OSi ?)3], depending on the conditions. Attempts to extract the species with coordinating solvents such as acetone and acetonitrile failed. Treatment with PPhi at low temperature ( <80 °C) and PhC?CPh at 150 °C in solution were also unsuccessful. Treatment with PMe3 at 65 °C and with PPh3 at 80 °C yielded [Ru3(CO)9(PMe3)3] and [Ru3(CO)9(PPh3)3], respectively. These results coupled with the similarities of IR spectra between the surface species and extracted compounds supported the postulated formula.