Reaction of ferrocenium ion with secondary phosphines: replacement of cyclopentadienyl ligand rather than its C—H functionalization

Reactions of Ferrocenium Hexafluorophosphate with P−OR Nucleophiles Give Ring C−H Functionalization or Ring Replacement Products Depending on the Phosphorus Reagent

“…[13] The other reaction is the replacement of the Cp ring itself with secondary phosphines to afford the half-sandwich complexes [CpFe(R 2 PH) 3 ] + . [14] In the course of our study, we have shown that the hydrogen substitution reactions proceed as an oxidative nucleophilic substitution in ferrocene (Scheme 1), which includes consecutive stages of nucleophilic exo-addition of a phosphine (a), redox transformation of IM1 involving the initial ferrocenium salt (b), and the final deprotonation (c).…”

“…Good additivity of R-group contributions to TEP allows one to estimate its value for ligands for which it has not been measured. [21] The values of both Tolman parameters for phosphorus nucleophiles studied earlier [11,13,14] and in this work are given in Table S1. Figure 2 shows the ligand cone angles plotted against TEPs; the color of points represents the type of the product.…”

“…On the contrary, the mechanism of the Cp-ring replacement in the reactions with PÀ OR nucleophiles and secondary phosphines [14] have never been discussed. Herein, we propose the mechanistic pathway for these reactions shown in Scheme 4.…”

“…It should be noted that a slight change in the structure of a phosphorus reagent (for instance, replacement of a tertiary phosphine with a secondary one) dramatically alters the reaction outcome: complexes [CpFe(R 2 PH) 3 ] + form instead of the expected ferrocenylphosphonium salts [CpFeC 5 H 4 PHR 2 ] + . [14] To the best of our knowledge, the formation of half-sandwich complexes from ferrocenium salts has no precedents.…”

Teaching cyclopentadienyl how to leave: a case study of the [CpIr(COD)Br]+ complex

“…More generally speaking, few reactions are known in which a complete substitution of the Cp ligand occurs. For instance, the reactions of ferrocenium with phosphites, 30 secondary phosphines, 31 and isonitriles 32 lead to the half-sandwich complexes [CpFeL 3 ] + . The electrophilic addition to nickelocene affords [CpNi(η 4 -C 5 H 5 R)] + (R = H, CPh 3 , C 7 H 7 ) followed by η 4 -ligand cleavage and the ultimate formation of [Cp 3 Ni 2 ] + , the first reported multidecker compound.…”