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.