Investigations of Iron–Nitrogen Bonding at Synthetic Iron–Sulfur Clusters
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sridharan-sridhara-phd-chemistry-2022-thesis.pdf
Description
Thesis PDF
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11.66 MB
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Checksum (MD5)
5a89470a51853707540b484f5a8c867a
Author(s)
Sridharan, Arun
Advisor(s)
Suess, Daniel L.M.
Date Issued
May 2022
Publisher
Massachusetts Institute of Technology
Abstract
The coordination chemistry of nitrogenous ligands at high-spin iron is investigated through the synthesis and characterization of a terminal imido complex of a cuboidal tetra(μ3-sulfido)tetrairon (Fe4S4) cluster. Structural, spectroscopic, and computational studies establish a dynamic interplay between Fe–N, Fe–S, and Fe–Fe interactions, tuned by the Fe centers’ locally high-spin electron configurations and the pseudo-C3v symmetry of the imido-bound metal site. Reaction with 1,4-cyclohexadiene affords clean conversion to the corresponding [Fe4S4] anilido complex, which was characterized in two oxidation states. Oxidation and reduction of the [Fe4S4] terminal imido complex affords a four-membered redox series spanning the 1−/0/1+/2+ charge states. A combined spectroscopic and theoretical analysis of this redox series using variable-temperature 1H nuclear magnetic resonance spectroscopy reveals that oxidation events are primarily centered at the imido fragment, which takes on an iminyl ([NAr]•−) or triplet nitrene ([NAr]2•) configuration depending on the charge state of the molecule. Two-electron oxidation of [Fe4S4]+ anilido complexes results in formal aminyl radical reductive elimination, generating aniline, hydrazine, and/or azoarene as byproducts along with the corresponding [Fe4S4]2+ solvento adduct. Addition of 1,2-diarylhydrazine to the [Fe4S4]+ solvento adduct results in N–N binuclear oxidative addition to afford the [Fe4S4]2+ anilido complex, which upon further reaction with 1,2-diarylhydrazines catalyzes their disproportionation to aniline and azoarene. The development of new synthetic platforms for investigating the reaction chemistry of iron–sulfur clusters is described: [MFe3S4] cluster cubanes are prepared varying the identity of the heterometal (Mo or V) and the steric profile of its supporting ligand for application in studies of dinitrogen binding and functionalization. The discovery of a new tridentate ligand topology for cuboidal [Fe4S4] clusters incorporating 1,1′-biphenyl-3,3′-diyl linkers is reported, along with strategies for metalating its tris(phosphine) derivative.
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Massachusetts Institute of Technology. Department of Chemistry
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