Reaction of trans-[ReOX 2 (EtO)(PPh 3 ) 2 ] (X = Cl, Br, I) with 4,6-dimethylpyrimidine-2-(1H)-thione (pymSH) in 1 : 1 molar ratio in refluxing acetone, rapidly formed [ReOX 2 (pymS)(PPh 3 )] (X = Cl, Br, I) compounds and PPh 3 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-[ReX 2 (pymS)(PPh 3 ) 2 ] (X = Cl, Br) species and triphenylphosphine oxide as a result of oxygen transfer from the [ReO] 3 + core to the PPh 3 . The trans-[ReX 2 (pymS) (PPh 3 ) 2 ] (X = Cl, Br) species, in organic solvents at room temperature and in the presence of atmospheric oxygen, are easily oxidized back to [ReOX 2 (pymS)(PPh 3 )] with the concomitant formation of O = PPh 3 . These oxidation reactions most likely proceed through the loss of a PPh 3 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 ([ReX 2 (pymS)(PPh 3 )(O 2 )]). 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-[ReX 2 (pymS)(PPh 3 ) 2 ] (X = Cl, Br) species, monitored by VIS-NIR and 1 H NMR spectroscopy. Spectroscopic (UV-VIS-NIR, 1 H and 3 1 P NMR), magnetic and electrochemical properties of the complexes are discussed.