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Updated: Jun 18, 2025

Characterizing Lewis Pairs Using Titration Coupled with In Situ Infrared Spectroscopy
Published on: February 20, 2020
Divergent Interaction of (Iso)nitriles with a Linear Iron(I) Silylamide─A Combined Structural, Spectroscopic, and
C Gunnar Werncke1, Igor Müller1, Kilian Weißer2
1Chemistry Department, Philipps-University Marburg, Hans-Meerwein-Straße 4, D-35043 Marburg, Germany.
Abstract:
Nitriles and isonitriles are important σ-donor ligands in coordination chemistry. Isonitriles also function in low-valent complexes as π-acceptor ligands similar to CO. Herein we present the unusual behavior of the highly reducing, high-spin iron(I) complex [Fe(hmds)2]- toward these compound classes. Rare examples of side-on coordination of nitriles to the metal center are observed. Insights gained by 57Fe Mössbauer spectroscopy as well as DFT and CASSCF calculations give an interplay between the resonance structures of not only an iron(I) π-complex and an iron(III) metallacycle but also point to the importance of an iron(II) nitrile radical anion. For an aromatic isonitrile end-on coordination is observed, which is best described as an iron(I) complex with only minor unpaired spin transfer onto the isonitrile. For aliphatic isonitriles, the selective R-CN bond cleavage occurs and yields stoichiometric mixtures of alkyl iron(II) and cyanido iron(II) complexes. Attempts to isolate presumed (iso)nitrile radical anions void of 3d-metal coordination give for the reaction of an aromatic isonitrile with KC8 facile reductive coupling to the corresponding diamido acetylene.
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