A structural investigation of the carbocation complex [{Cp∗(CO)2Fe}2{μ-(C3H5)}]PF6

The reaction of the propanediyl complex [{Cp∗(CO)2Fe}2{μ-(C3H6)}] (Cp∗ = η5-C5(CH3)5) with the hydride abstractor Ph3CPF6 in dry CH2Cl2 resulted in the formation of the carbocation complex [{Cp∗(CO)2Fe}2{μ-(C3H5)}]PF6. The complex formed triclinic crystals in the space group P1¯ with Z = 1. In the structure one metal is bonded in the η2-fashion, forming a chiral metallacyclopropane structure with the carbocation, while the other is σ-bonded to the same carbocation ligand. However, NMR evidence indicates that the structure observed in the solid state is not preserved in solution because the metallacyclopropane ring opens up, giving a structure in which more positive charge is localized on the β-CH carbon and which could be fluxional.

The Fe(II) carbocation complex [{Cp∗(CO)2Fe}2{μ-(C3H5)}]PF6 has been prepared by reacting the neutral bimetallic complex [{Cp∗(CO)2Fe}2{μ-(C3H6)}] with 1 equiv. of Ph3CPF6 in dry CH2Cl2. The NMR data and crystal structure of the carbocation complex are reported and show a metallocyclopropane structure in the solid state and a transition metal-stabilized carbenium ion in solution.Figure optionsDownload as PowerPoint slide