The secondary phosphine-substituted (at cobalt) mixed-metal dicobalt–iron complex [Co 2Fe(μ 3-S)(CO) 8(PPh 2H)] ( 1) can be prepared in good yield from the reaction of [Co 2Fe(μ 3-S)(CO) 9] with one equivalent of Ph 2PH in toluene. Also isolated in the reaction, as minor products, are the disubstituted (both at cobalt) complex [Co 2Fe(μ 3-S)(CO) 7(PPh 2H) 2] ( 2) and the trisubstituted species [Co 2Fe(μ 3-S)(CO) 6(PPh 2H) 3] ( 3). Thermolysis of 1 or 2 results in PH bond cleavage and the formation of the bis-phosphido-bridged species [Co 2Fe(μ 3-S)(μ-PPh 2) 2(CO) 6] ( 4) and [Co 2Fe(μ 3-S)(μ-PPh 2) 2(CO) 5(PPh 2H)] ( 5). Complex 5 can also be prepared more directly by treatment of 4 with one equivalent of Ph 2PH. The X-ray structure of the PhPMe 2 analogue of 5, [Co 2Fe(μ 3-S)(μ-PPh 2) 2(CO) 5(PPhMe 2)] ( 5′), reveals the phosphine to be cobalt-bound and occupying an equatorial site. Carbonylation of 4 results in coupling of one phosphido group with the sulphur cap to give the thiophosphine-bridged complex [Co 2Fe(μ 3-SPPh 2)(μ-PPh 2)(CO) 7] ( 6), while treatment of 1 with n-BuLi followed by RSCH 2Cl (R=Me, Ph) results in the formation of the previously reported thiophosphinomethane-bridged species [Co 2Fe(μ 3-S)(μ-PPh 2CH 2SR)(CO) 8] (R=Me 7a, Ph 7b). In contrast, interaction of 1 with n-BuLi followed by successive treatment with carbon disulphide and methyl iodide yields the dithiomethoxycarbonylphosphine-bridged complex [Co 2Fe(μ 3-S){μ-PPh 2C(SMe)S}(CO) 8] ( 8). Single crystal X-ray diffraction studies have been performed on complexes 5′ and 8.