The reduction of [(Cp'''Co)(2)(mu,eta(2:2)-P-2)(2)] (CP''' = 1,2,4-tBu(3)C(5)H(2)) with the samarocenes, [(C5Me4R)(2)Sm-(THF)(n)] (R = Me or n-propyl), gives [(Cp'''Co)(2)P4Sm(C5Me4R)(2)]. This is the first example of an intramolecular P-P coupling in a polyphosphide complex upon reduction of the transition metal. The formation of the P-P bond is not a result of the direct reduction of the phosphorus atoms but is induced by a rearrangement-of the positive charges between the metal atoms.