Treatment of methyltrioxorhenium(VII), MTO, with the dithiol o-HSC6H4CH2SH results in a dimeric rhenium(V) chelate, [CH3Re(O)(S-2(L))](2), where S-2(L) is the diithiolate ligand present as a chelate. The dimer is monomerized upon reaction with triphenylphosphine, giving the intensely green CH3(Ph3P)Re(O)(S-2(L)). The dimer reverts to MTO upon treatment with certain oxygen donors XO, such as pyridine-NO and Ph3AsO.