Nucleophilic Functionalization of a Cationic Pentaphosphole Complex-A Systematic Study of Reactivity

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), O^tBu (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.