The first 4d/4f polyphosphides were obtained by reaction of the divalentmetallocenes [Cp*(2)Ln(thf)(2)] (Ln = Sm, Yb) with [{CpMo(CO)(2)}(2)(mu,eta(2:2)-P-2)] or [Cp*Mo(CO)(2)(eta(3)-P-3)]. Treatment of [Cp*(2)Ln(thf)(2)] (Ln = Sm, Yb) with [{CpMo(CO)(2)}(2)(mu,eta(2:2)-P-2)] gave the 16-membered bicyclic compounds [(Cp-2*L-n)(2)P-2(CpMo(CO)(2))(4)] (Ln = Sm, Yb) as the major products. From the reaction involving samarocene, the cyclic P-4 complex [(Cp*Sm-2)(2)P-4(CpMo(CO)(2))(2)] and the cyclic P-5 complex [(Cp*Sm-2)(3)P-5(CpMo(CO)(2))(3)] were also obtained as minor products. In each reaction, the P-2 unit is reduced and a rearrangement occurred. In dedicated cases, a P-P bond formation takes place, which results in a new aggregation of the central phosphorus scaffold. In the reactions of [Cp*(2)Ln(thf)(2)] (Ln = Sm, Yb) with [Cp*Mo(CO)(2)P-3] a new P-P bond is formed by reductive dimerization and the 4d/4f hexaphosphides [(Cp*(2)Ln)(2)P-6(Cp*Mo(CO)(2))(2)] (Ln = Sm, Yb) were obtained.