Redox Interconversion of [ReVO]3+  [Re(III)]3+ Centers in Octahedral 4,6-Dimethyl-Pyrimidine-2-Thiolate/Triphenylphosphine Rhenium(V) and Rhenium(III) Mixed Complexes

Reaction of trans-[ReOX2(EtO)(PPh3)2] (X = CI, Br, 1) with 4,6-dimethylpyrimidine-2-(l H)-thione(pymSH) in 1:1 molar ratio in refluxing acetone, rapidly formed [ReOX2(pymS)(PPh3)] (X = C1, Br, I)compounds and PPh~ in good yields. Upon increasing the refluxing time (5-6 h), the above products react ina 1:2 molar ratio producing the paramagnetic trans-[ReX2(pymS)(PPh3)2] (X = CI, Br) species and triphenylphosphineoxide as a result of oxygen transfer from the [ReO] 3+ core to the PPh3. The trans-[ReX2(pymS)(PPh3)2] (X = CI, Br) species, in organic solvents at room temperature and in the presence of atmosphericoxygen, are easily oxidized back to [ReOX2(pymS)(PPh~)] with the concomitant formation ofO = PPh3. Theseoxidation reactions most likely proceed through the loss of a PPh, ligand on the reducing rhenium(IIl) center,which makes a coordination site available for the oxidative addition of dioxygen which produces a highlyreactive rhenium-dioxygen intermediate ([ReX2(pymS)(PPh3)(02)]). The time course of the aerial oxygenationreactions at room temperature was inferred from the rate [Kin = (1.30 + 0.05) x 10 2 h t] of disappearanceof the paramagnetic trans-[ReX2(pymS)(PPh3)2] (X = C1, Br) species, monitored by VIS-NIR and ~H NMRspectroscopy. Spectroscopic (UV-VIS-NIR, ~H and 3~p NMR), magnetic and electrochemical properties of thecomplexes are discussed.