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Exploring the Limits of Dative Boratrane Bonding: Iron as a Strong Lewis Base in Low-Valent Non-Heme Iron-Nitrosyl Complexes

Dong, Hai T. and Chalkley, Matthew J. and Oyala, Paul H. and Zhao, Jiyong and Alp, E. Ercan and Hu, Michael Y. and Peters, Jonas C. and Lehnert, Nicolai (2020) Exploring the Limits of Dative Boratrane Bonding: Iron as a Strong Lewis Base in Low-Valent Non-Heme Iron-Nitrosyl Complexes. Inorganic Chemistry, 59 (20). pp. 14967-14982. ISSN 0020-1669. PMCID PMC7640944. doi:10.1021/acs.inorgchem.0c01686.

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We previously reported the synthesis and preliminary characterization of a unique series of low-spin (ls) {FeNO}⁸⁻¹⁰ complexes supported by an ambiphilic trisphosphineborane ligand, [Fe(TPB)(NO)]^(+/0/−). Herein, we use advanced spectroscopic techniques and density functional theory (DFT) calculations to extract detailed information as to how the bonding changes across the redox series. We find that, in spite of the highly reduced nature of these complexes, they feature an NO+ ligand throughout with strong Fe−NO π-backbonding and essentially closed-shell electronic structures of their FeNO units. This is enabled by an Fe−B interaction that is present throughout the series. In particular, the most reduced [Fe(TPB)(NO)]− complex, an example of a ls-{FeNO}¹⁰ species, features a true reverse dative Fe → B bond where the Fe center acts as a strong Lewis-base. Hence, this complex is in fact electronically similar to the ls-{FeNO}⁸ system, with two additional electrons “stored” on site in an Fe−B single bond. The outlier in this series is the ls-{FeNO}⁹ complex, due to spin polarization (quantified by pulse EPR spectroscopy), which weakens the Fe−NO bond. These data are further contextualized by comparison with a related N₂ complex, [Fe(TPB)(N₂)]⁻, which is a key intermediate in Fe(TPB)-catalyzed N₂ fixation. Our present study finds that the Fe → B interaction is key for storing the electrons needed to achieve a highly reduced state in these systems, and highlights the pitfalls associated with using geometric parameters to try to evaluate reverse dative interactions, a finding with broader implications to the study of transition metal complexes with boratrane and related ligands.

Item Type:Article
Related URLs:
URLURL TypeDescription CentralArticle
Dong, Hai T.0000-0002-8914-3045
Chalkley, Matthew J.0000-0002-0484-7335
Oyala, Paul H.0000-0002-8761-4667
Zhao, Jiyong0000-0002-0777-3626
Alp, E. Ercan0000-0002-4803-8863
Hu, Michael Y.0000-0002-3718-7169
Peters, Jonas C.0000-0002-6610-4414
Lehnert, Nicolai0000-0002-5221-5498
Additional Information:© 2020 American Chemical Society. Received: June 8, 2020; Published: September 29, 2020. This work was supported by grants from the National Science Foundation (CHE-1608331 and CHE-2002855 to NL) and the National Institutes of Health (GM 070757 to JCP). HTD acknowledges support from the Eastman Summer Research Fellowship and the Robert W. Parry Scholarship. MJC acknowledges support from the Resnick Sustainability Institute at Caltech. The Caltech EPR facility was supported by the Dow Next Generation Educator Fund. The authors declare no competing financial interest.
Group:Resnick Sustainability Institute
Funding AgencyGrant Number
NIHGM 070757
Eastman Summer Research FellowshipUNSPECIFIED
Robert W. Parry ScholarshipUNSPECIFIED
Resnick Sustainability InstituteUNSPECIFIED
Dow Next Generation Educator FundUNSPECIFIED
Issue or Number:20
PubMed Central ID:PMC7640944
Record Number:CaltechAUTHORS:20200929-105404784
Persistent URL:
Official Citation:Exploring the Limits of Dative Boratrane Bonding: Iron as a Strong Lewis Base in Low-Valent Non-Heme Iron-Nitrosyl Complexes. Hai T. Dong, Matthew J. Chalkley, Paul H. Oyala, Jiyong Zhao, E. Ercan Alp, Michael Y. Hu, Jonas C. Peters, and Nicolai Lehnert. Inorganic Chemistry 2020 59 (20), 14967-14982; DOI: 10.1021/acs.inorgchem.0c01686
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105634
Deposited By: Tony Diaz
Deposited On:29 Sep 2020 18:09
Last Modified:12 Feb 2022 00:27

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