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

Abstract

AbstractFerrocenium hexafluorophosphate reacts with different P−OR nucleophiles (PR3) in CH2Cl2 at room temperature to give either half‐sandwich complexes [CpFe(PR3)3](PF6) (PR3=P(OMe)3, P(OEt)3, PhP(OMe)2) or ferrocenylphosphonium salts [CpFe(C5H4PR3)](PF6) (PR3=iPr2P(OMe), iPr2P(OEt)). Mixtures of both products are formed for some other nucleophiles (PR3=Ph2P(OMe), Ph2P(OEt), PhP(OiPr)2). The mechanism of the former reaction was established using DFT calculations. This reaction pathway is especially characteristic of π‐acceptor nucleophiles, which is presumably explained by their ability to stabilize the 19e intermediates. The result of the reaction with tertiary phosphines, aminophosphines, and P−OR nucleophiles can be reliably predicted based on the values of the Tolman electronic parameter (below 2070 cm−1 – only ferrocenylphosphonium salt, in between 2073 cm−1 and 2080 cm−1 – only half‐sandwich complex, and in the range from 2070 cm−1 to 2073 cm−1 – mixtures of both products).