The systematic nucleophilic functionalization of the cationic pentaphosphole ligand complex [Cp*Fe(η4-P5Me)][OTf] (A) with group 16/17 nucleophiles is reported. This method represents a highly reliable and versatile strategy for the design of novel transition-metal complexes featuring twofold substituted end-deck cyclo-P5 ligands, bearing unprecedented hetero-element substituents. By the reaction of A with classical group 16 nucleophiles, complexes of the type [Cp*Fe(η4-P5MeE)] (E=OEt (1), OtBu (2), SPh (3), SePh (4)) are obtained. By transferring this protocol to group 17 nucleophiles, the highly sensitive complexes [Cp*FeP5(η4-P5MeX)] (X=F (5), Cl (6), Br (7), I (8)) could be isolated. All products show exclusively 1,1'-substitution at the cyclo-P5 ring. Interestingly, further studies on the reactivity of the halogenated species revealed their ability to undergo ring-opening reactions with cyclic ethers such as THF and ethylene oxide yielding [Cp*FeP5(η4-P5MeOC4H8X)] (X=Br (9), I (10)) or [Cp*FeP5(η4-P5MeOC2H4X)] (X=Br (11), I (12)), respectively. Furthermore, the use of acyclic ethers such as dimethoxyethane led to the formation of [Cp*FeP5(η4-P5MeOC2H4OCH3)] (13) mediated by C−O bond cleavage, followed by subsequent P−O bond formation, as further enlightened by DFT calculations.