Redox interconversion of [RevO]3+?[ReIII]3+ centers in octahedral 4,6-dimethyl-pyrimidine-2-thiolate/triphenylphosphine rhenium(V) and rhenium (III) mixed complexes

Article abstract of DOI:10.1016/S0277-5387(96)00505-0

Reaction of trans-[ReOX₂(EtO)(PPh₃)₂] (X = Cl, Br, I) with 4,6-dimethylpyrimidine-2-(1H)-thione (pymSH) in 1:1 molar ratio in refluxing acetone, rapidly formed [ReOX₂(pymS) (PPh₃)] (X = Cl, Br, I) compounds and PPh₃ in good yields. Upon increasing the refluxing time (5-6 h), the above products react in a 1:2 molar ratio producing the paramagnetic trans-[ReX₂(pymS)(PPh₃)₂] (X = Cl, Br) species and triphenylphosphine oxide as a result of oxygen transfer from the [ReO]³⁺ core to the PPh₃. The trans-[ReX₂(pymS) (PPh₃)₂] (X = Cl, Br) species, in organic solvents at room temperature and in the presence of atmospheric oxygen, are easily oxidized back to [ReOX₂(pymS)(PPh₃)] with the concomitant formation of O = PPh₃. These oxidation reactions most likely proceed through the loss of a PPh₃ ligand on the reducing rhenium(III) center, which makes a coordination site available for the oxidative addition of dioxygen which produces a highly reactive rhenium-dioxygen intermediate ([ReX₂(pymS)(PPh₃(O₂)]). The time course of the aerial oxygenation reactions at room temperature was inferred from the rate [K_m = (1.30 ± 0.05) × 10^-2 h^-1] of disappearance of the paramagnetic trans-[ReX₂(pymS)(PPh₃)₂] (X = Cl, Br) species, monitored by VIS-NIR and ¹H NMR spectroscopy. Spectroscopic (UV-VIS-NIR. ¹H and ³¹P NMR), magnetic and electrochemical properties of the complexes are discussed.