The secondary phosphine-substituted (at cobalt) mixed-metal dicobalt-iron complex [Co 2 Fe(μ 3 -S)(CO) 8 (PPh 2 H)] (1) can be prepared in good yield from the reaction of [Co 2 Fe(μ 3 -S)(CO) 9 ] with one equivalent of Ph 2 PH in toluene. Also isolated in the reaction, as minor products, are the disubstituted (both at cobalt) complex [Co 2 Fe(μ 3 -S)(CO) 7 (PPh 2 H) 2 ] (2) and the trisubstituted species [Co 2 Fe(μ 3 -S)(CO) 6 (PPh 2 H) 3 ] (3). Thermolysis of 1 or 2 results in P H bond cleavage and the formation of the bis-phosphido-bridged species [Co 2 Fe(μ 3 -S)(μ-PPh 2 ) 2 (CO) 6 ] (4) and [Co 2 Fe(μ 3 -S)(μ-PPh 2 ) 2 (CO) 5 (PPh 2 H)] (5). Complex 5 can also be prepared more directly by treatment of 4 with one equivalent of Ph 2 PH. The X-ray structure of the PhPMe 2 analogue of 5, [Co 2 Fe(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 2 Fe(μ 3 -SPPh 2 )(μ-PPh 2 )(CO) 7 ] (6), while treatment of 1 with n-BuLi followed by RSCH 2 Cl (R=Me, Ph) results in the formation of the previously reported thiophosphinomethane-bridged species [Co 2 Fe(μ 3 -S)(μ-PPh 2 CH 2 SR)(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 2 Fe(μ 3 -S){μ-PPh 2 C(SMe) S}(CO) 8 ] (8). Single crystal X-ray diffraction studies have been performed on complexes 5' and 8.