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Zars E, Pick L, Swain A, Bhunia M, Carroll PJ, Munz D, Meyer K, Mindiola DJ. Iron-Catalyzed Intermolecular C-H Amination Assisted by an Isolated Iron-Imido Radical Intermediate. Angew Chem Int Ed Engl 2023:e202311749. [PMID: 37815099 DOI: 10.1002/anie.202311749] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2023] [Revised: 10/02/2023] [Accepted: 10/03/2023] [Indexed: 10/11/2023]
Abstract
Here we report the use of a base metal complex [(tBu pyrpyrr2 )Fe(OEt2 )] (1-OEt2 ) (tBu pyrpyrr2 2- =3,5-tBu2 -bis(pyrrolyl)pyridine) as a catalyst for intermolecular amination of Csp3 -H bonds of 9,10-dihydroanthracene (2 a) using 2,4,6-trimethyl phenyl azide (3 a) as the nitrene source. The reaction is complete within one hour at 80 °C using as low as 2 mol % 1-OEt2 with control in selectivity for single C-H amination versus double C-H amination. Catalytic C-H amination reactions can be extended to other substrates such as cyclohexadiene and xanthene derivatives and can tolerate a variety of aryl azides having methyl groups in both ortho positions. Under stoichiometric conditions the imido radical species [(tBu pyrpyrr2 )Fe{=N(2,6-Me2 -4-tBu-C6 H2 )] (1-imido) can be isolated in 56 % yield, and spectroscopic, magnetometric, and computational studies confirmed it to be an S = 1 FeIV complex. Complex 1-imido reacts with 2 a to produce the ferrous aniline adduct [(tBu pyrpyrr2 )Fe{NH(2,6-Me2 -4-tBu-C6 H2 )(C14 H11 )}] (1-aniline) in 45 % yield. Lastly, it was found that complexes 1-imido and 1-aniline are both competent intermediates in catalytic intermolecular C-H amination.
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Affiliation(s)
- Ethan Zars
- Department of Chemistry, University of Pennsylvania, 231 S 34th St, Philadelphia, PA-19104, USA
| | - Lisa Pick
- Department of Chemistry & Pharmacy, Inorganic Chemistry, Friedrich-Alexander-Universität Erlangen - Nürnberg (FAU), 91058, Erlangen, Germany
| | - Abinash Swain
- Inorganic Chemistry: Coordination Chemistry, Saarland University, Campus C4 1, 66123, Saarbrücken, Germany
| | - Mrinal Bhunia
- Department of Chemistry, University of Pennsylvania, 231 S 34th St, Philadelphia, PA-19104, USA
| | - Patrick J Carroll
- Department of Chemistry, University of Pennsylvania, 231 S 34th St, Philadelphia, PA-19104, USA
| | - Dominik Munz
- Inorganic Chemistry: Coordination Chemistry, Saarland University, Campus C4 1, 66123, Saarbrücken, Germany
| | - Karsten Meyer
- Department of Chemistry & Pharmacy, Inorganic Chemistry, Friedrich-Alexander-Universität Erlangen - Nürnberg (FAU), 91058, Erlangen, Germany
| | - Daniel J Mindiola
- Department of Chemistry, University of Pennsylvania, 231 S 34th St, Philadelphia, PA-19104, USA
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Barchenko M, O’Malley PJ, de Visser SP. Mechanism of Nitrogen Reduction to Ammonia in a Diiron Model of Nitrogenase. Inorg Chem 2023; 62:14715-14726. [PMID: 37650683 PMCID: PMC10498488 DOI: 10.1021/acs.inorgchem.3c02089] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2023] [Indexed: 09/01/2023]
Abstract
Nitrogenase is a fascinating enzyme in biology that reduces dinitrogen from air to ammonia through stepwise reduction and protonation. Despite it being studied in detail by experimental and computational groups, there are still many unknown factors in the catalytic cycle of nitrogenase, especially related to the addition of protons and electrons and their order. A recent biomimetic study characterized a potential dinitrogen-bridged diiron cluster as a synthetic model of nitrogenase. Using strong acid and reductants, the dinitrogen was converted into ammonia molecules, but details of the mechanism remains unknown. In particular, it was unclear from the experimental studies whether the proton and electron transfer steps are sequential or alternating. Moreover, the work failed to establish what the function of the diiron core is and whether it split into mononuclear iron fragments during the reaction. To understand the structure and reactivity of the biomimetic dinitrogen-bridged diiron complex [(P2P'PhFeH)2(μ-N2)] with triphenylphosphine ligands, we performed a density functional theory study. Our computational methods were validated against experimental crystal structure coordinates, Mössbauer parameters, and vibrational frequencies and show excellent agreement. Subsequently, we investigated the alternating and consecutive addition of electrons and protons to the system. The calculations identify a number of possible reaction channels, namely, same-site protonation, alternating protonation, and complex dissociation into mononuclear iron centers. The calculations show that the overall mechanism is not a pure sequential set of electron and proton transfers but a mixture of alternating and consecutive steps. In particular, the first reaction steps will start with double proton transfer followed by an electron transfer, while thereafter, there is another proton transfer and a second electron transfer to give a complex whereby ammonia can split off with a low energetic barrier. The second channel starts with alternating protonation of the two nitrogen atoms, whereafter the initial double proton transfer, electrons and protons are added sequentially to form a hydrazine-bound complex. The latter split off ammonia spontaneously after further protonation. The various reaction channels are analyzed with valence bond and orbital diagrams. We anticipate the nitrogenase enzyme to operate with mixed alternating and consecutive protonation and electron transfer steps.
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Affiliation(s)
- Maxim Barchenko
- Manchester
Institute of Biotechnology, The University
of Manchester, 131 Princess Street, Manchester M1 7DN, U.K.
- Department
of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
| | - Patrick J. O’Malley
- Department
of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
| | - Sam P. de Visser
- Manchester
Institute of Biotechnology, The University
of Manchester, 131 Princess Street, Manchester M1 7DN, U.K.
- Department
of Chemical Engineering, The University
of Manchester, Oxford
Road, Manchester M13 9PL, U.K.
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Bhutto SM, Hooper RX, Mercado BQ, Holland PL. Mechanism of Nitrogen-Carbon Bond Formation from Iron(IV) Disilylhydrazido Intermediates during N 2 Reduction. J Am Chem Soc 2023; 145:4626-4637. [PMID: 36794981 DOI: 10.1021/jacs.2c12382] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023]
Abstract
We recently reported a reaction sequence that activates C-H bonds in simple arenes as well as the N-N triple bond in N2, delivering the aryl group to N2 to form a new N-C bond (Nature 2020, 584, 221). This enables the transformation of abundant feedstocks (arenes and N2) into N-containing organic compounds. The key N-C bond forming step occurs upon partial silylation of N2. However, the pathway through which reduction, silylation, and migration occurred was unknown. Here, we describe synthetic, structural, magnetic, spectroscopic, kinetic, and computational studies that elucidate the steps of this transformation. N2 must be silylated twice at the distal N atom before aryl migration can occur, and sequential silyl radical and silyl cation addition is a kinetically competent pathway to a formally iron(IV)-NN(SiMe3)2 intermediate that can be isolated at low temperature. Kinetic studies show its first-order conversion to the migrated product, and DFT calculations indicate a concerted transition state for migration. The electronic structure of the formally iron(IV) intermediate is examined using DFT and CASSCF calculations, which reveal contributions from iron(II) and iron(III) resonance forms with oxidized NNSi2 ligands. The depletion of electron density from the Fe-coordinated N atom makes it electrophilic enough to accept the incoming aryl group. This new pathway for the N-C bond formation offers a method for functionalizing N2 using organometallic chemistry.
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Affiliation(s)
- Samuel M Bhutto
- Department of Chemistry, Yale University, 225 Prospect St., New Haven, Connecticut 06520, United States
| | - Reagan X Hooper
- Department of Chemistry, Yale University, 225 Prospect St., New Haven, Connecticut 06520, United States
| | - Brandon Q Mercado
- Department of Chemistry, Yale University, 225 Prospect St., New Haven, Connecticut 06520, United States
| | - Patrick L Holland
- Department of Chemistry, Yale University, 225 Prospect St., New Haven, Connecticut 06520, United States
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Hakey BM, Leary DC, Lopez LM, Valerio LR, Brennessel WW, Milsmann C, Matson EM. Synthesis and Characterization of Pyridine Dipyrrolide Uranyl Complexes. Inorg Chem 2022; 61:6182-6192. [PMID: 35420825 PMCID: PMC9044449 DOI: 10.1021/acs.inorgchem.2c00348] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The first actinide complexes of the pyridine dipyrrolide (PDP) ligand class, (MesPDPPh)UO2(THF) and (Cl2PhPDPPh)UO2(THF), are reported as the UVI uranyl adducts of the bulky aryl substituted pincers (MesPDPPh)2- and (Cl2PhPDPPh)2- (derived from 2,6-bis(5-(2,4,6-trimethylphenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine (H2MesPDPPh, Mes = 2,4,6-trimethylphenyl), and 2,6-bis(5-(2,6-dichlorophenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine (H2Cl2PhPDPPh, Cl2Ph = 2,6-dichlorophenyl), respectively). Following the in situ deprotonation of the proligand with lithium hexamethyldisilazide to generate the corresponding dilithium salts (e.g., Li2ArPDPPh, Ar = Mes of Cl2Ph), salt metathesis with [UO2Cl2(THF)2]2 afforded both compounds in moderate yields. The characterization of each species has been undertaken by a combination of solid- and solution-state methods, including combustion analysis, infrared, electronic absorption, and NMR spectroscopies. In both complexes, single-crystal X-ray diffraction has revealed a distorted octahedral geometry in the solid state, enforced by the bite angle of the rigid meridional (ArPDPPh)2- pincer ligand. The electrochemical analysis of both compounds by cyclic voltammetry in tetrahydrofuran (THF) reveals rich redox profiles, including events assigned as UVI/UV redox couples. A time-dependent density functional theory study has been performed on (MesPDPPh)UO2(THF) and provides insight into the nature of the transitions that comprise its electronic absorption spectrum.
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Affiliation(s)
- Brett M Hakey
- Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
| | - Dylan C Leary
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Lauren M Lopez
- Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
| | - Leyla R Valerio
- Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
| | - William W Brennessel
- Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
| | - Carsten Milsmann
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Ellen M Matson
- Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
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