Abstract The reaction between Re 2(CO) 10 and a number of organo-phosphanes and phosphites in refluxing xylene have been studied. With P(OPh) 3, the products are 1,2-diaxial-Re 2(CO) 8L 2 and 1-axial-2,2′-axial, equatorial-Re 2(CO) 7L 3, whereas with ( o-CH 3C 6H 4O) 3P, 1,2-diaxial-Re 2(CO) 8L 2 and the metalated complex Re(CO) 3L(LH) are formed. In the case of ( p-ClC 6H 4O) 3P, only 1,2-diaxial-Re 2(CO) 8L 2 was isolated. ( p-CH 3C 6H 4) 3P and (cyclohexyl) 3P both yield 1,2-diaxial-Re 2(CO) 8L 2 and mer- trans-HRe(CO) 3L 2, however, ( o-CH 3C 6H 4) 3P gives only the metalated product, Re(CO) 4LH. Formation of the hydrides and metalated compounds is rationalised in terms of the homolysis of the metalmetal bonded dimers to yield metal-centred free radical intermediates. The behaviour of the dimers and the radical intermediates is discussed in terms of the properties of the phosphorus donor ligands.