A trinuclear rhenium sulfide cluster complex, [(Ph3P)(2)N][Re-3(mu(3)-S)(mu-S)(3)Cl-6(PMe2Ph)(3)], synthesized from Re3S7Cl7, dimethylphenylphosphine, and [(Ph3P)(2)N]Cl is readily converted to a bridging SO2 complex, [(Ph3P)(2)N][Re-3(mu(3)-S)(mu-S)(2)(mu-SO2)Cl-6(PMe2Ph)(3)], by reaction with O-2. The oxygen atoms on the SO2 ligand react with phosphines or phosphites to form phosphine oxides or phosphates, and the original cluster complex is recovered. The reaction course has been monitored by P-31 NMR as well as by UV-vis spectroscopy. The catalytic oxygenation of PMePh2 in the presence of the SO2 complex shows that turnovers are 8 per hour at 23 degrees C in CDCl3. The X-ray structures of the cluster complexes are described.