Coordination Chemistry of P(4)S(3) and P(4)Se(3) towards the Iron Fragments [Fe(Cp)(CO)(2)](+) and [Fe(Cp)(PPh(3))(CO)](+)

The complexes Ag(L)(n)[WCA] (L=P(4)S(3), P(4)Se(3), As(4)S(3), and As(4)S(4); [WCA]=[Al(OR(F))(4)](−) and [F{Al(OR(F))(3)}(2)](−); R(F)=C(CF(3))(3); WCA=weakly coordinating anion) were tested for their performance as ligand‐transfer reagents to transfer the poorly soluble nortricyclane cages P(4)S(3), P(4)Se(3), and As(4)S(3) as well as realgar As(4)S(4) to different transition‐metal fragments. As(4)S(4) and As(4)S(3) with the poorest solubility did not yield complexes. However, the more soluble silver‐coordinated P(4)S(3) and P(4)Se(3) cages were transferred to the electron‐poor Fp (+) moiety ([CpFe(CO)(2)](+)). Thus, reaction of the silver salt in the presence of the ligand with Fp−Br yielded [Fp−P(4)S(3)][Al(OR(F))(4)] (1 a), [Fp−P(4)S(3)][F(Al(OR(F))(3))(2)] (1 b), and [Fp−P(4)Se(3)][Al(OR(F))(4)] (2). Reactions with P(4)S(3) also yielded [FpPPh(3)−P(4)S(3)][Al(OR(F))(4)] (3), a complex with the more electron‐rich monophosphine‐substituted Fp (+) analogue [FpPPh(3)](+) ([CpFe(PPh(3))(CO)](+)). All complex salts were characterized by single‐crystal XRD, NMR, Raman, and IR spectroscopy. Interestingly, they show characteristic blueshifts of the vibrational modes of the cage, as well as structural contractions of the cages upon coordination to the Fp/FpPPh(3) moieties, which oppose the typically observed cage expansions that lead to redshifts in the spectra. Structure, bonding, and thermodynamics were investigated by DFT calculations, which support the observed cage contractions. Its reason is assigned to σ and π donation from the slightly P−P and P−E antibonding P(4)E(3)‐cage HOMO (e symmetry) to the metal acceptor fragment.