Immobilisation of methyltrioxorhenium on functionalised MCM-41

Methyltrioxorhenium (MTO) was immobilised in the mesoporous silica MCM-41 functionalised with a pyrazolylpyridine ligand. Elemental analysis indicated that the rhenium. loading in the final material (3.6 wt.%, 0.19 mmol g(-1)) was about 35% of the ligand content. Powder X-ray diffraction confirmed that the regular hexagonal symmetry of the host was preserved during the grafting experiments. The functionalised material was also characterised by C-13 and Si-29 magic-angle spinning NMR, FTIR and Raman spectroscopy. Analysis of the vibrational spectra was supported by preparing a model complex containing the ligand ethyl[3-(2-pyridyl)-1-pyrazolyl]acetate and by carrying out ab initio calculations. The results indicate that bidentate and monodentate coordination of the N-base ligand to the rhenium centre coexist for the model complex in the solid state. In solution, O-17-NMR spectroscopy for the model complex indicates a dynamic behaviour without a solely bidentate coordination even at low temperature. The coordination seems to be relatively weak, even for a monodentate adduct. For MTO immobilised in MCM-41 functionalised with the pyrazolylpyridine ligand, monodentate coordination of the pyridyl nitrogen atom to the metal centre was also found to be the major form present. (c) 2005 Elsevier Inc. All rights reserved.