The reaction of metallophosphanides with ML_nX leads to the formation of mixed-metal clusters via complexes that consist of a metallophosphine coordinated through the lone pair on the phosphorus atom to another metal fragment. This synthetic strategy has been employed to initially form trinuclear complexes with the general formula [(Ph₂PML_n)(OC)₂Co(μ-DMAD)Mo(CO)₂Cp] (ML_n = Mn(CO)₅3, WCp(CO)₂4, FeCp(CO)₂5; DMAD = dimethylacetylenedicarboxylate) from the reaction of the anion [(Ph₂P)(OC)₂Co(μ-DMAD)Mo(CO)₂Cp]⁻, 2, with metal halide complexes, ML_nX (X = Cl, Br). The complexes 3, 4 and 5 have been characterised spectroscopically, and an X-ray crystal structure of 5 shows that the Ph₂PFe(CO)₂Cp unit has coordinated to the cobalt centre through the lone pair on the phosphorus centre. Subsequent heating of 3 leads to carbonyl loss, and metal–metal bond formation, to yield [(OC)₆CpCoMnMo(μ-CO)(μ-PPh₂)(μ₃-η²(//)-DMAD)], 6. An X-ray structure determination of 6 confirms that it contains a ‘closed’ metal triangle. In a related series of reactions the cluster anion [Os₃(CO)₁₀(μ-PPh₂)]⁻ was treated with a variety of metal-containing synthons, ML_nX. With [FeCp(CO)₂Cl] the cluster [Os₃(CO)₁₀FeCp(CO)(μ-PPh₂)(μ-CO)] 9 was obtained in good yield, and has been shown crystallographically to consist of an osmium triangle ‘spiked’ by an iron atom, with the Os–Fe bond bridged by the PPh₂ group and a carbonyl ligand. With [(Ph₃P)MCl] (M = Ag, Au) the tetranuclear ‘butterfly’ clusters [Os₃(CO)₁₀(μ-PPh₂)(μ-MPR₃)] (10: M = Au, R = Ph; 11: M = Ag, R = Me) are obtained. These two complexes have been characterised spectroscopically and crystallographically.