Chromophoric lewis base adducts of methyltrioxorhenium: Synthesis, catalysis and photochemistry

A series of chromophoric Lewis base adducts of methyltrioxorhenium (MTO) was examined. The ligands were pyridine derivatives with different size of the aromatic system and variable substituents, thus providing a variation of electronic and steric parameters. The complexes were fully characterised (UV/Vis, IR and NMR spectroscopy, single-crystal X-ray diffraction and elemental analysis) and their stability constants in dichloromethane were determined by means of UV/Vis spectroscopy. Moreover, this report presents a study of the influence of these N-donor ligands coordinated to MTO on the catalytic activity of epoxidation of 1-octene. Each compound was tested twice; in a catalytic reaction under exclusion of light and in daylight. No significant differences in catalytic performance were found. The behaviour of the complexes under irradiation with UV light viras investigated by means of ¹⁷O-NMR and UV/Vis spectroscopy. The herein exposed experiments aimed for probing potential beneficial effects of chromophoric N-donor ligands in MTO adducts, as they might activate the catalytic system by providing additional energy for weakening bonds that have to be broken during the catalytic cycle.