The reactions of 1,1'-bis(diphenylphosphino)ferrocene diselenide (dppfSe2) with [Ru 3 (CO) 1 2 ] at 60 and 110 o C afford, respectively, the two isomeric nido-clusters [Ru 3 (μ 3 -Se) 2 (dppf)(CO) 7 ] (2) and [Ru 3 (μ 3 -Se) 2 (CO) 7 (μ-dppf)] (3) which contain dppf as chelating and bridging ligand, respectively. The chelated derivative 2, attainable under kinetic control, can be converted to the more stable bridged cluster 3 by thermal treatment in toluene solution. Moreover the cluster [Ru 3 Se{μ-P(Ph)C 5 H 4 FeC 5 H 4 PPh 2 }(μ-OCPh)(CO) 6 ] (4) was isolated as a minor product. Its cluster core consists of a metal triangle capped by a selenium atom and bridged on two sides, respectively, by a phosphido ligand and by a benzoyl group both deriving from multiple fragmentation of dppf diselenide and migratory insertion of a Ph ring into a CO ligand. Isomers 2 and 3 present different electrochemical behaviour, the bridged one giving a more complicated voltammetric pattern.