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

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, 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, 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) x 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 H-1 NMR spectroscopy. Spectroscopic (UV-VIS-NIR, H-1 and P-31 NMR), magnetic and electrochemical properties of the complexes are discussed. (C) 1997 Elsevier Science Ltd.