The triphosphorus complex Mo2Cp2(μ-η3:η3-P3)­(μ-P t Bu2) was prepared in 83% yield by reacting the methyl complex Mo2Cp2(μ-κ1:η2-CH3)­(μ-P t Bu2)­(μ-CO) with P4 at 333 K, a process also giving small amounts of the methyldiphosphenyl complex Mo2Cp2(μ-η2:η2-P2Me)­(μ-P t Bu2)­(CO)2. The latter could be better prepared by first reacting the anionic complex Na­Mo2Cp2­(μ-P t Bu2)­(μ-CO)2 with P4 to give the diphosphorus derivative Na­Mo2Cp2(μ-η2:η2-P2)­(μ-P t Bu2)­(CO)2 and further reaction of the latter with MeI. Density functional theory calculations on the title complex revealed that its triphosphorus group can be viewed as an allylic-like P3 – ligand acting as a six-electron donor via the external P atoms, while coordination of the internal P atom involves donation from the π orbital of the ligand and back-donation to its π* orbital, both interactions having a weakening effect on the Mo–Mo and P–P connections. The reactivity of the title compound is dominated by the electron-donor ability associated with the lone pairs located at the P atoms. Its reaction with CF3SO3Me gave Mo2Cp2(μ-η3:η3-P3Me)­(μ-P t Bu2)­(CF3SO3) as a result of methylation at an external atom of the P3 ligand, while its reaction with Fe2(CO)9 enabled the addition of one, two, or three Fe­(CO)4 fragments at these P atoms, but only the diiron derivative Mo2Fe2Cp2(μ-η3:η3:κ1:κ1-P3)­(μ-P t Bu2)­(CO)8 could be isolated. This complex bears a Fe­(CO)4 fragment at each of the external atoms of the P3 ligand, and the central P atom of the latter displays the lowest 31P chemical shift reported to date (δP −721.8 ppm). The related complexes Mo2M2Cp2(μ-η3:η3:κ1:κ1-P3)­(μ-P t Bu2)­(CO)10 (M = Mo, W) were prepared by reacting the title compound with the corresponding M­(CO)5(THF) complexes in toluene, while reaction with Mo­(CO)4(THF)2 also enabled the formation of the heptanuclear derivative Mo7Cp4(μ-η3:η3:κ1:κ1-P3)2(μ-P t Bu2)2(CO)14. The interatomic distances in the above compounds indicate that the central Mo2P3 skeleton of these molecules is little modified by the attachment of 16-electron M­(CO) n fragments at the external atoms of the P3 ligand.