Selective substitution and insertion reactions of silylenes into the cyclo-P, ring of [Cp*Fe(eta(5)-P-5)] are reported. The selective substitution of one P atom by an isoelectronic [LSi] fragment (L = PhC((NBu)-Bu-t)(2)) leads to [(eta(4)-P4SiL)FeCp*] and [LSi(Cl)=P-SiL(Cl)(2)]. To elucidate the reaction mechanism, [{LSi(N(SiMe3)(2))}{(eta(4)-P-5)FeCp*}], in which the silicon atom binds to the cyclo-P-5 ring, was synthesized as a model compound for the reaction intermediate. The insertion of [LSi-SiL] into the cyclo-P-5 ring of [Cp*Fe(eta(5)-P-5)] resulted in [{eta(4)-P-5(SiL)(2)}FeCp*] featuring a cyclo-P-5(SiL)(2) ring, which corresponds to the largest silicon-polyphosphorus ring known in a complex.