The interaction of monodentate N-donor ligands to MTO methyltrioxorhenium) is governed by both electronic and steric effects. For example, the formation constant of pyridine to MTO is 215.76 L mol-1, whereas that of the better donor 4-picoline is 703.14 L mol-1 and that of the sterically encumbered 2-picoline is <1 L mol-1.
Formation constants have been evaluated for this reaction, MTO + L= MTO.L, where L comprises monodentate N-donor ligands. A successful correlation of log K with pKa of L was realized except in the case of 2-substituted ligands.