2024/11/12 by Alexandra L. Nagelski, Majed S. Fataftah, Samantha N. MacMillan +5 · 1 voice
Chemistry · Energy · Engineering · #Organometallic Complex Synthesis and Catalysis #Metalloenzymes and iron-sulfur proteins #Molecular Junctions and Nanostructures
paper · doi:10.1021/jacs.4c08358
openalex publication_date 2024/11/12 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
Carbon monoxide inhibited forms of nitrogenases have carbonyl (CO) and carbide (C 4– ) bridges, which are common in synthetic iron complexes with strong-field ligand environments but rare in iron sites with weak-field ligand environments analogous to the enzyme. Here, we explore the fundamental bonding description of bridging CO in high-spin iron systems. We describe the isolation of several diiron carbonyls and related species, and elucidate their electronic structures, magnetic coupling, and characteristic structural and vibrational parameters. These high-spin iron complexes exhibit equivalent π-backbonding abilities to low-spin iron complexes. Sequential reduction and silylation of a formally diiron(I) bridging CO complex ultimately gives a formally diiron(IV) bridging carbyne complex. Despite the large range of formal oxidation states across this series, X-ray absorption spectroscopy and density functional theory calculations indicate that the electron density at the iron sites does not change. Thus, the [Fe(μ-CO)] 2 core undergoes redox changes at the bridging carbonyls rather than the metal centers, rendering the metal’s formal oxidation state misleading. The ability of the Fe 2 C 2 core to easily shift charge between the metals and the ligands has implications for nitrogenases, and for other multinuclear systems for redox catalysis.