Addition of tri(2-furyl)phosphine, PFu 3 , to [Os 3 (CO) 10 (μ-H) 2 ] at room temperature gives [HOs 3 (CO) 10 (PFu 3 )(μ-H)] (1), while in refluxing toluene the same reactants afford [Os 3 (CO) 9 {μ 3 -PFu 2 (C 4 H 2 O)}(μ-H)] (2) resulting from orthometallatation of a furyl ring. Reaction of PFu 3 with [Os 3 (CO) 10−n (NCMe) n ] (n=0, 1, 2) affords the substituted clusters [Os 3 (CO) 12−n (PFu 3 ) n ] (n=1–3) (3–5), the phosphine ligands occupying equatorial position in all cases. Heating [Os 3 (CO) 11 (PFu 3 )] (3) in refluxing octane gives [Os 3 (CO) 9 (μ 3 -PFu)(μ 3 -η 2 -C 4 H 2 O)] (6) which results from both carbon–hydrogen and carbon–phosphorus bond activation and contains both μ 3 -η 2 -furyne and furylphosphinidene ligands. All new clusters have been characterized by spectroscopic methods together with single crystal X-ray diffraction for 2, 3 and 6.