Adduct Formation and Stability of Methyltrioxorhenium(VII) with a Series of Aliphatic and Aromatic Nitrogen–Donor Ligands

The stability of a variety of aromatic and aliphatic N-donor ligands adducts of methyltrioxorhenium(VII) (CH3ReO3, MTO) was investigated using acetonitrile (CH3CN) as a solvent. The formation constants were determined by utilization of the obtained spectrophotometric data based on a 1:1 adduct formations. The adduct formation constants (Kf) for MTO:L (L = nitrogen donor ligand) are very sensitive to the electronic nature of the ligand and increases with the ligand donating ability. Adducts of aliphatic N-donor ligands are less stable towards decomposition by basic solutions and produce polymeric rhenium material, methane and perrhenate. The kinetics of the adduct decomposition were investigated in solution at room temperature under pseudo-first-order conditions. Linear correlations between the adduct decomposition rate constants (kd) and (Ka) values of the N-donor ligand have shown that the decomposition rate constants increasing with the N-donor ligand basicity. A comparative study between the values of Kf and kd revealed that imidazole forms the most stable adduct with MTO among the N-donor ligands investigated in this study.