Cationic isonitrile complexes of the CpFe(CO)2 fragment

•Four novel cationic iron(II) isonitrile complexes synthesized.•Quantum chemical calculations on eight cationic iron(II) isonitrile complexes.•Correlations between a series of calculated data and the Hammett parameter σp.•No correlation with the NC-stretching frequency.

[CpFe(CO)2(THF)]+BF4− undergoes exchange of the labile THF ligand against isonitriles resulting in a shift of the NC-stretching vibration to higher energies compared to the free isonitriles. Quantum chemical calculations show that this shift is not a real indicator for the electronic character and thus the electronic influence of the substituents at the para-functionalized phenylisonitriles. In contrast, other calculated parameters such as reactions enthalpies, Fe–C distances, charges and CO-stretching frequencies clearly correlate with the Hammett constant σp.

Graphical abstractThe energy of the NC-stretching vibration of phenylisonitriles is not indicative for the substituents' influence at the phenyl ring.Figure optionsDownload full-size imageDownload as PowerPoint slide