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Increase of Direct C-C Coupling Reaction Yield by Identifying Structural and Electronic Properties of High-Spin Iron Tetra-azamacrocyclic Complexes

Brewer, Samantha M.; Wilson, Kevin R.; Jones, Donald G.; Reinheimer, Eric W.; Archibald, Stephen J.; Prior, Timothy J.; Ayala, Megan A.; Foster, Alexandria L.; Hubin, Timothy J.; Green, Kayla N.

Authors

Samantha M. Brewer

Kevin R. Wilson

Donald G. Jones

Eric W. Reinheimer

Megan A. Ayala

Alexandria L. Foster

Timothy J. Hubin

Kayla N. Green



Abstract

Macrocyclic ligands have been explored extensively as scaffolds for transition metal catalysts for oxygen and hydrogen atom transfer reactions. C–C reactions facilitated using earth abundant metals bound to macrocyclic ligands have not been well-understood but could be a green alternative to replacing the current expensive and toxic precious metal systems most commonly used for these processes. Therefore, the yields from direct Suzuki–Miyaura C–C coupling of phenylboronic acid and pyrrole to produce 2-phenylpyrrole facilitated by eight high-spin iron complexes ([Fe3+L1(Cl)2]+, [Fe3+L4(Cl)2]+, [Fe2+L5(Cl)]+, [Fe2+L6(Cl)2], [Fe3+L7(Cl)2]+, [Fe3+L8(Cl)2]+, [Fe2+L9(Cl)]+, and [Fe2+L10(Cl)]+) were compared to identify the effect of structural and electronic properties on catalytic efficiency. Specifically, catalyst complexes were compared to evaluate the effect of five properties on catalyst reaction yields: (1) the coordination requirements of the catalyst, (2) redox half-potential of each complex, (3) topological constraint/rigidity, (4) N atom modification(s) increasing oxidative stability of the complex, and (5) geometric parameters. The need for two labile cis-coordination sites was confirmed based on a 42% decrease in catalytic reaction yield observed when complexes containing pentadentate ligands were used in place of complexes with tetradentate ligands. A strong correlation between iron(III/II) redox potential and catalytic reaction yields was also observed, with [Fe2+L6(Cl)2] providing the highest yield (81%, −405 mV). A Lorentzian fitting of redox potential versus yields predicts that these catalysts can undergo more fine-tuning to further increase yields. Interestingly, the remaining properties explored did not show a direct, strong relationship to catalytic reaction yields. Altogether, these results show that modifications to the ligand scaffold using fundamental concepts of inorganic coordination chemistry can be used to control the catalytic activity of macrocyclic iron complexes by controlling redox chemistry of the iron center. Furthermore, the data provide direction for the design of improved catalysts for this reaction and strategies to understand the impact of a ligand scaffold on catalytic activity of other reactions.

Journal Article Type Article
Publication Date Aug 6, 2018
Journal Inorganic Chemistry
Print ISSN 0020-1669
Electronic ISSN 1520-510X
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 57
Issue 15
Pages 8890-8902
APA6 Citation Brewer, S. M., Wilson, K. R., Jones, D. G., Reinheimer, E. W., Archibald, S. J., Prior, T. J., …Green, K. N. (2018). Increase of Direct C-C Coupling Reaction Yield by Identifying Structural and Electronic Properties of High-Spin Iron Tetra-azamacrocyclic Complexes. Inorganic chemistry, 57(15), 8890-8902. https://doi.org/10.1021/acs.inorgchem.8b00777
DOI https://doi.org/10.1021/acs.inorgchem.8b00777
Keywords Physical and Theoretical Chemistry; Inorganic Chemistry
Publisher URL https://pubs.acs.org/doi/10.1021/acs.inorgchem.8b00777
Copyright Statement This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher.
To access the final edited and published work see the links in this record.

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Copyright Statement
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher.
To access the final edited and published work see the links in this record.



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