Chloro(eta(5)-cyclopentadienyl)tris(trimethylphosphine)- molybdenum(III) tetrafluoroborate, [MoCl(C5H5)-(C3H9P)(3)][BF4], was obtained from the oxidation of [MoH(C5H5)(PMe(3))(3)] by AgBF4, followed by crystallization from dichloromethane. Chloro(eta(5)-pentamethyl-cyclopentadienyl) tris (trimethylphosphine) molybdenum-(III) hexafluorophosphate, [MoCl(C10H15)(C3H9P)(3)]-[PF6], was obtained from the reaction of [MoCl2-(C10H15)(C3H9P)(2)] With T1PF(6) and PMe(3) in dichloromethane. Both cations adopt a four-legged piano-stool arrangement.