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Activation of an Open Shell, Carbyne-Bridged Diiron Complex Toward Binding of Dinitrogen

Arnett, Charles H. and Agapie, Theodor (2020) Activation of an Open Shell, Carbyne-Bridged Diiron Complex Toward Binding of Dinitrogen. Journal of the American Chemical Society, 142 (22). pp. 10059-10068. ISSN 0002-7863. doi:10.1021/jacs.0c01896.

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Binding of N₂ by nitrogenase requires a reductive activation of the FeMo-cofactor, but the precise structure and atomic composition of FeMoco in its activated form is not well understood. However, recent crystallographic studies suggest that N₂ reduction may occur at a carbon-bridged diiron subunit of FeMoco. Toward modeling the activation of a Fe–(μ-C)–Fe site toward N₂ binding, we synthesized a new dinucleating, hexaphosphine ligand derived from a 2,6-disubstituted toluene platform. Activation of the central methyl group of the ligand affords the diiron μ-carbyne complex (P₆ArC)Fe₂ (μ-H) featuring a biologically relevant Fe(μ-carbyne)(μ-H)Fe motif. SQUID magnetometry, Mössbauer spectroscopy, and DFT calculations reveal that (P₆ArC)Fe₂ (μ-H) has a well-isolated S = 1 ground state, distinguishing it from all other diiron μ-carbyne complexes which are diamagnetic. Upon the addition of sources of H⁺/e⁻ (H₂, TEMPO-H or HCl), (P₆ArC)Fe₂ (μ-H) is activated toward N₂ binding, with concomitant protonation of the carbyne ligand. Although reaction with H₂ ultimately leads to complete protonation of the carbyne moiety, mechanistic investigations indicate that formation of a single C–H bond, with concomitant cleavage of one Fe–C bond, generates an iron-carbene intermediate capable of coordinating N₂.

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Arnett, Charles H.0000-0002-1272-3797
Agapie, Theodor0000-0002-9692-7614
Additional Information:© 2020 American Chemical Society. Received: February 21, 2020; Published: April 14, 2020. We are grateful to the NSF for funding (CHE-1905320 to T.A. and an NSF Graduate Research Fellowship to C.H.A.). We thank Prof. Jonas C. Peters for insightful discussions and for the use of his group’s Mössbauer spectrometer. We thank Michael Takase and Lawrence Henling for assistance with X-ray crystallography and David VanderVelde for assistance with NMR spectroscopy. Magnetic data was acquired at the University of California, Los Angeles with assistance from Dr. Ignacio Martini on a Quantum Design MPMS3 SQUID Magnetometer supported by the NSF (MRI-1625776). The Dow Next Generation Educator Fund is acknowledged for X-ray diffraction and NMR instrumentation. The computations presented here were conducted on the Caltech High Performance Cluster partially supported by a grant from the Gordon and Betty Moore Foundation. The authors declare no competing financial interest.
Funding AgencyGrant Number
NSF Graduate Research FellowshipUNSPECIFIED
Dow Next Generation Educator FundUNSPECIFIED
Gordon and Betty Moore FoundationUNSPECIFIED
Issue or Number:22
Record Number:CaltechAUTHORS:20200519-081454400
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Official Citation:Activation of an Open Shell, Carbyne-Bridged Diiron Complex Toward Binding of Dinitrogen. Charles H. Arnett and Theodor Agapie. Journal of the American Chemical Society 2020 142 (22), 10059-10068 DOI: 10.1021/jacs.0c01896; doi: 10.1021/jacs.0c01896
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103300
Deposited By: Tony Diaz
Deposited On:19 May 2020 16:18
Last Modified:16 Nov 2021 18:20

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