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Electronic Structures of an [Fe(NNR_2)]^(+/0/–) Redox Series: Ligand Noninnocence and Implications for Catalytic Nitrogen Fixation

Thompson, Niklas B. and Oyala, Paul H. and Dong, Hai T. and Chalkley, Matthew J. and Zhao, Jiyong and Alp, E. Ercan and Hu, Michael and Lehnert, Nicolai and Peters, Jonas C. (2019) Electronic Structures of an [Fe(NNR_2)]^(+/0/–) Redox Series: Ligand Noninnocence and Implications for Catalytic Nitrogen Fixation. Inorganic Chemistry, 58 (5). pp. 3535-3549. ISSN 0020-1669. PMCID PMC6598684. doi:10.1021/acs.inorgchem.9b00133.

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The intermediacy of metal–NNH_2 complexes has been implicated in the catalytic cycles of several examples of transition-metal-mediated nitrogen (N_2) fixation. In this context, we have shown that triphosphine-supported Fe(N_2) complexes can be reduced and protonated at the distal N atom to yield Fe(NNH_2) complexes over an array of charge and oxidation states. Upon exposure to further H^+/e^– equivalents, these species either continue down a distal-type Chatt pathway to yield a terminal iron(IV) nitride or instead follow a distal-to-alternating pathway resulting in N–H bond formation at the proximal N atom. To understand the origin of this divergent selectivity, herein we synthesize and elucidate the electronic structures of a redox series of Fe(NNMe_2) complexes, which serve as spectroscopic models for their reactive protonated congeners. Using a combination of spectroscopies, in concert with density functional theory and correlated ab initio calculations, we evidence one-electron redox noninnocence of the “NNMe_2” moiety. Specifically, although two closed-shell configurations of the “NNR_2” ligand have been commonly considered in the literature—isodiazene and hydrazido(2−)—we provide evidence suggesting that, in their reduced forms, the present iron complexes are best viewed in terms of an open-shell [NNR_2]^•–ligand coupled antiferromagnetically to the Fe center. This one-electron redox noninnocence resembles that of the classically noninnocent ligand NO and may have mechanistic implications for selectivity in N_2 fixation activity.

Item Type:Article
Related URLs:
URLURL TypeDescription Information CentralArticle
Thompson, Niklas B.0000-0003-2745-4945
Oyala, Paul H.0000-0002-8761-4667
Dong, Hai T.0000-0002-8914-3045
Chalkley, Matthew J.0000-0002-0484-7335
Zhao, Jiyong0000-0002-0777-3626
Alp, E. Ercan0000-0002-4803-8863
Hu, Michael0000-0002-3718-7169
Lehnert, Nicolai0000-0002-5221-5498
Peters, Jonas C.0000-0002-6610-4414
Alternate Title:Electronic Structures of an [Fe(NNR2)]+/0/– Redox Series: Ligand Noninnocence and Implications for Catalytic Nitrogen Fixation
Additional Information:© 2019 American Chemical Society. Received: January 14, 2019; Published: February 14, 2019. This work was supported by the Resnick Sustainability Institute at Caltech (a graduate fellowship to N.B.T.), as well as the NIH (Grant GM 070757). The EPR facility at the California Institute of Technology is supported by the NSF via its MRI program (Grant NSF-1531940) and the Dow Next Generation Educator Fund. The authors declare no competing financial interest.
Group:Resnick Sustainability Institute
Funding AgencyGrant Number
Resnick Sustainability InstituteUNSPECIFIED
NIHGM 070757
Dow Next Generation Educator FundUNSPECIFIED
Issue or Number:5
PubMed Central ID:PMC6598684
Record Number:CaltechAUTHORS:20190214-104228298
Persistent URL:
Official Citation:Electronic Structures of an [Fe(NNR2)]+/0/– Redox Series: Ligand Noninnocence and Implications for Catalytic Nitrogen Fixation. Niklas B. Thompson, Paul H. Oyala, Hai T. Dong, Matthew J. Chalkley, Jiyong Zhao, E. Ercan Alp, Michael Hu, Nicolai Lehnert, and Jonas C. Peters. Inorganic Chemistry 2019 58 (5), 3535-3549. DOI: 10.1021/acs.inorgchem.9b00133
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92933
Deposited By: Tony Diaz
Deposited On:14 Feb 2019 19:46
Last Modified:16 Feb 2022 00:11

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